9111L-AUTO-11/14
General Features
●Single-package fully-integrated Atmel® AVR® 8-bit microcontroller with LIN
transceiver, 5V regulator (85mA current capability) and watchdog
●Very low current consumption in sleep mode
●8Kbytes/16Kbytes flash memory for application program (Atmel
ATA6612C/ATA6613C)
●Supply voltage up to 40V
●Operating voltage: 5V to 27V
●Temperature range: Tcase –40°C to +125°C
●QFN48, 7mm × 7mm package
Description
Atmel ATA6612C/ATA6613C is a system-in-package (SiP) product, which is particularly
suited for complete LIN-bus slave-node applications. I consists of two ICs in one package
supporting highly integrated solutions for in-vehicle LIN networks. The first chip is the
LIN-system-basis-chip (LIN-SBC) Atmel ATA6624, which has an integrated LIN
transceiver, a 5V regulator and a window watchdog. The second chip is an automotive
microcontroller from Atmel series of Atmel AVR 8-bit microcontroller with advanced RISC
architecture.
The Atmel ATA6612C consists of the LIN-SBC Atmel ATA6624 and the Atmel ATmega88
with 8Kbytes flash. The Atmel ATA6613C consists of the LIN-SBC Atmel ATA6624 and the
Atmel ATmega168 with 16Kbytes flash. All pins of the LIN system basis chip as well as all
pins of the Atmel AVR microcontroller are bonded out to provide customers the same
flexibility for their applications as they have when using discrete parts.
In section 2 you will find the pin configuration for the complete SiP. In sections 3 to 5 the
LIN SBC is described, and in sections 6 to 7 the Atmel AVR is described in detail.
ATA6612C/ATA6613C
8K/16K Flash Microcontroller with LIN Transceiver, 5V
Regulator and Watchdog
DATASHEET
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
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Figure 1. Application Diagram
MCU Atmel
ATmega88
or
ATmega168
Atmel ATA6612C/ATA6613C
LIN-SBC
Atmel
ATA6624
LIN Bus
3
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
1. Pin Configuration
Figure 1-1. Pinning QFN48, 7mm × 7mm
Table 1-1. Pin Description
Pin Symbol Function
1PB5 Port B 5 I/O line (SCK / PCINT5)
2MCUAVCC Microcontroller ADC-unit supply voltage (referred to as AVCC pin in Section 5. “Microcontroller
Block” on page 27 and Section 6. “2-wire Serial Interface Characteristics” on page 276)
3ADC6 ADC input channel 6
4AREF Analog reference voltage input
5GND4 Ground
6ADC7 ADC input channel 7
7PC0 Port C 0 I/O line (ADC0/PCINT8)
8PC1 Port C 1 I/O line (ADC1/PCINT9)
9PC2 Port C 2 I/O line (ADC2/PCINT10)
10 PC3 Port C 3 I/O line (ADC3/PCINT11)
11 PC4 Port C 4 I/O line (ADC4/SDA/PCINT12)
12 PC5 Port C 5 I/O line (ADC5/SCL/PCINT13)
13 PC6 Port C 6 I/O line (RESET/PCINT14)
14 PD0 Port D 0 I/O line (RXD/PCINT16)
15 PD1 Port D 1 I/O line (TXD/PCINT17)
16 PD2 Port D 2 I/O line (INT0/PCINT18)
17(1) RXD Receive data output
18(1) INH High side switch output for controlling an external voltage regulator
19(1) TXD Transmit data input / active low output after a local wake up request
Note: 1. This identifies the pins of the LIN SBC Atmel ATA6624
Atmel
ATA6612C/
ATA6613C
48 47 46 45 44 43 42 41 40 39 38 37
13
1
14 15 16 17 18 19 20 21 22 23 24
2
3
4
5
6
7
8
9
10
11
12
PB5
MCUAVCC
ADC6
AREF
GND4
ADC7
PC0
PC1
PC2
PC3
PC4
PC5
PC6
PD0
PD1
PD2
RXD
INH
TXD
NRES
WD_OSC
TM
MODE
KL_15
PB4
PB3
PB2
PB1
PB0
PD7
PD6
PD5
PB7
PB6
MCUVCC
GND2
MCUVCC
GND1
PD4
PD3
LIN
GND
WAKE
NTRIG
EN
VS
VCC
PVCC
36
35
34
33
32
31
30
29
28
27
26
25
ATA6612C/ATA6613C [DATASHEET]
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20(1) NRES Watchdog and under voltage reset output (open drain)
21(1) WD_OSC External resistor for adjustable watchdog timing
22(1) TM Tie to ground – for factory use only
23(1) MODE Connect to GND for normal watchdog operation or connect to VCC for debug mode
24(1) KL_15 Ignition detection (edge sensitive)
25(1) PVCC Voltage regulator sense input
26(1) VCC Voltage regulator output
27(1) VS Battery connection
28(1) EN LIN-transceiver enable input
29(1) NTRIG Watchdog trigger input (negative edge)
30(1) WAKE System-basis-chip external wake-up input
31(1) GND Analog system GND
32(1) LIN LIN-bus input/output
33 PD3 Port D 3 I/O line (INT1 OC2B/PCINT19)
34 PD4 Port D 4 I/O line (T0/XCK/PCINT20)
35 GND1 Ground
36 MCUVCC Microcontroller supply voltage (referred to as VCC pin in Section 5. “Microcontroller Block” on
page 27 and Section 6. “2-wire Serial Interface Characteristics” on page 276)
37 GND2 Ground
38 MCUVCC Microcontroller supply voltage (referred to as VCC pin in Section 5. “Microcontroller Block” on
page 27 and Section 6. “2-wire Serial Interface Characteristics” on page 276)
39 PB6 Port B 6 I/O line (TOSC1/XTAL1/PCINT6)
40 PB7 Port B 7 I/O line (TOSC2/XTAL2/PCINT7)
41 PD5 Port D 5 I/O line (T1/OC0B/PCINT21)
42 PD6 Port D 6 I/O line (AIN0/OC0A PCINT22)
43 PD7 Port D 7 I/O line (AIN1/PCINT23)
44 PB0 Port B 0 I/O line (ICP1/CLKO/PCINT0)
45 PB1 Port B 1 I/O line (OC1A/PCINT1)
46 PB2 Port B 2 I/O line (OC1B/SS/PCINT2)
47 PB3 Port B 3 I/O line (MOSI/OC2A/PCINT3)
48 PB4 Port B 4 I/O line (MISO/PCINT4)
Backside Heat slug is connected to GND
Table 1-1. Pin Description (Continued)
Pin Symbol Function
Note: 1. This identifies the pins of the LIN SBC Atmel ATA6624
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ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
2. Absolute Maximum Ratings
Table 2-1. Maximum Ratings of the SiP
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a
stress rating only and functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended
periods may affect device reliability.
Parameters Symbol Min. Typ. Max. Unit
HBM ESD
ANSI/ESD -STM5.1
JESD22 -A114
AEC-Q100 (002)
±2 KV
CDM ESD STM 5.3.1
Corner pins (1, 12, 13, 24, 25, 36, 37, 48)
All other pins
750
500
V
V
Machine model ESD AEC-Q100-Rev.F (003) ±100 V
ESD according to IBEE LIN EMC
Test Spec. 1.0 following IEC 61000-4-2
- Pin VS, LIN, KL_15 (47kΩ/100nF) to GND
- Pin WAKE (33 kΩ serial resistor) to GND
±6
±5
KV
KV
ESD HBM following STM5.1 with 1.5kΩ 100pF
- Pin VS, LIN, KL_15, WAKE to GND ±6 KV
Storage temperature Ts–55 +150 °C
Operating temperature(1) Tcase –40 +125 °C
Thermal resistance junction to heat slug Rthjc 5K/W
Thermal resistance junctiion to ambient Rthja 25 K/W
Thermal shutdown of VCC regulator 150 165 170 °C
Thermal shutdown of LIN output 150 165 170 °C
Thermal shutdown hysteresis 10 °C
Note: 1. Tcase means the temperature of the heat slug (backside). It is mandatory that this backside temperature is
≤125°C in the application.
ATA6612C/ATA6613C [DATASHEET]
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Table 2-2. Maximum Ratings of the LIN-SBC
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a
stress rating only and functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended
periods may affect device reliability.
Parameters Symbol Min. Typ. Max. Unit
Supply voltage VSVS–0.3 +40 V
Pulse time ≤500ms; Ta = 25°C
Output current IVCC ≤ 85mA VS+40 V
Pulse time ≤ 2min; Ta = 25°C
Output current IVCC ≤ 85mA VS27 V
WAKE (with 33kΩ serial resistor)
KL_15 (with 47kΩ/100nF)
DC voltage
Transient voltage due to ISO7637 (coupling
1nF)
–1
–150
+40
+100
V
V
INH
- DC voltage –0.3 VS + 0.3 V
LIN
- DC voltage –27 +40 V
Logic pins (RxD, TxD, EN, NRES, NTRIG,
WD_OSC, MODE, TM) –0.3 +5.5 V
Output current NRES INRES +2 mA
PVCC DC voltage
VCC DC voltage
–0.3
–0.3
+5.5
+6.5
V
V
Table 2-3. Maximum Ratings of the Microcontroller
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a
stress rating only and functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended
periods may affect device reliability.
Parameters Symbol Min. Typ. Max. Unit
Voltage on any pin except RESET with respect
to ground –0.5 MCUVCC +
0.5 V
Voltage on RESET with respect to ground –0.5 13.0 V
Maximum operating voltage 6.0 V
DC current per I/O pin 40.0 mA
DC current MCUVCC and GND pins 200.0 mA
Injection current at MCUVCC = 0V(1) ±5.0 mA
Injection current at MCUVCC = 5V ±1.0 mA
Note: 1. Maximum current per port = ±30mA
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ATA6612C/ATA6613C [DATASHEET]
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3. LIN System-basis-chip Block
3.1 Features
●Master and slave operation possible
●Supply voltage up to 40V
●Operating voltage VS = 5V to 27V
●Typically 10µA supply current during sleep mode
●Typically 57µA supply current in silent mode
●Linear low-drop voltage regulator, 85mA current capability:
●Normal, fail-safe, and silent mode
●VCC = 5.0V ±2%
●In sleep mode VCC is switched off
●VCC - undervoltage detection (4ms reset time) and watchdog reset logical combined at open drain output NRES
●Negative trigger input for watchdog
●Boosting the voltage regulator possible with an external NPN transistor
●LIN physical layer according to LIN 2.0, 2.1 specification and SAEJ2602-2
●Wake-up capability via LIN-bus, wake pin, or Kl_15 pin
●INH output to control an external voltage regulator or to switch off the master pull Up resistor
●TXD time-out timer
●Bus pin is over temperature and short circuit protected versus GND and battery
●Adjustable watchdog time via external resistor
●Advanced EMC and ESD performance
●Fulfills the OEM “hardware requirements for LIN in automotive applications Rev.1.0”
●Interference and damage protection according ISO7637
ATA6612C/ATA6613C [DATASHEET]
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3.2 Description
The LIN-SBC ATA6624 is a fully integrated LIN transceiver, which complies with the LIN 2.0, 2.1 and SAEJ2602-2
specifications. It has a low-drop voltage regulator for 5V/85mA output and a window watchdog. The voltage regulator is able
to source up to 85mA, but the output current can be boosted by using an external NPN transistor.
The LIN-SBC is designed to handle the low-speed data communication in vehicles, e.g., in convenience electronics.
Improved slope control at the LIN-driver ensures secure data communication up to 20kBaud. Sleep mode and silent mode
guarantee very low current consumption.
Figure 3-1. Block Diagram
Adjustable
Watchdog
Oscillator
Short Circuit and
Overtemperature
Protection
TXD
Time-out
Timer
Edge
Detection
Debounce
Time
Internal Testing
Unit
Control Unit
Slew Rate Control
Wake-up
Bus Timer
Mode Select
Undervoltage
Reset
Normal/Silent/
Fail-safe Mode
5V
RF Filter
Watchdog
OUT
RXD
GND
NTRIG
PVCC
PVCC
PVCC
TMMODE
EN
TXD
KL_15
WAKE
Receiver
-
+
Normal
Mode
Normal and
Fail-safe
Mode
LIN
WD_OSC
NRES
PVCC
VCC
VS
INH
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ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
3.3 Functional Description
3.3.1 Physical Layer Compatibility
Since the LIN physical layer is independent from higher LIN layers (e.g., the LIN protocol layer), all nodes with a LIN physical
layer according to revision 2.x can be mixed with LIN physical layer nodes, which are according to older versions (i.e., LIN
1.0, LIN 1.1, LIN 1.2, LIN 1.3), without any restrictions.
3.3.2 Supply Pin (VS)
The LIN operating voltage is VS = 5V to 27V. An under voltage detection is implemented to disable data transmission if VS
falls below VSth < 4V in order to avoid false bus messages. After switching on VS, the IC starts in fail-safe mode, and the
voltage regulator is switched on (i.e., output capability).
The supply current is typically 10µA in sleep mode and 57µA in silent mode.
3.3.3 Ground Pin (GND)
The IC does not affect the LIN bus in the event of GND disconnection. It is able to handle a ground shift up to 11.5% of
versus The mandatory system ground is pin 5.
3.3.4 Voltage Regulator Output Pin (VCC)
The internal voltage regulator is capable of driving loads with up to 85mA. It is able to supply the microcontroller and other
ICs on the PCB and is protected against overloads by means of current limitation and over temperature shut-down.
Furthermore, the output voltage is monitored and will cause a reset signal at the NRES output pin if it drops below a defined
threshold Vthun. To boost up the maximum load current, an external NPN transistor may be used, with its base connected to
the VCC pin and its emitter connected to PVCC.
3.3.5 Voltage Regulator Sense Pin (PVCC)
The PVCC is the sense input pin of the voltage regulator. For normal applications (i.e., when only using the internal output
transistor), this pin is connected to the VCC pin. If an external boosting transistor is used, the PVCC pin must be connected
to the output of this transistor, i.e., its emitter terminal.
3.3.6 Bus Pin (LIN)
A low-side driver with internal current limitation and thermal shutdown and an internal pull-up resistor compliant with the LIN
2.x specification are implemented. The allowed voltage range is between –27V and +40V. Reverse currents from the LIN
bus to VS are suppressed, even in the event of GND shifts or battery disconnection. LIN receiver thresholds are compatible
with the LIN protocol specification. The fall time from recessive to dominant bus state and the rise time from dominant to
recessive bus state are slope controlled.
3.3.7 Input/Output Pin (TXD)
In normal mode the TXD pin is the microcontroller interface used to control the state of the LIN output. TXD must be pulled to
ground in order to have a low LIN-bus. If TXD is high or unconnected (internal pull-up resistor), the LIN output transistor is
turned off, and the bus is in recessive state. During fail-safe mode, this pin is used as output. It is current-limited to < 8mA.
and is latched to low if the last wake-up event was from pin WAKE or KL_15.
3.3.8 TXD Dominant Time-out Function
The TXD input has an internal pull-up resistor. An internal timer prevents the bus line from being driven permanently in
dominant state. If TXD is forced to low for longer than tDOM > 6ms, the LIN-bus driver is switched to recessive state.
To reactivate the LIN bus driver, switch TXD to high (>10µs).
3.3.9 Output Pin (RXD)
The output pin reports the state of the LIN-bus to the microcontroller. LIN high (recessive state) is reported by a high level at
RXD; LIN low (dominant state) is reported by a low level at RXD. The output has an internal pull-up resistor with typically
5kΩ to VCC. The AC characteristics can be defined with an external load capacitor of 20pF.
The output is short-circuit protected. RXD is switched off in Unpowered mode (i.e., VS = 0V).
ATA6612C/ATA6613C [DATASHEET]
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3.3.10 Enable Input Pin (EN)
The enable Input pin controls the operation mode of the device. If EN is high, the circuit is in normal mode, with transmission
paths from TXD to LIN and from LIN to RXD both active. The VCC voltage regulator operates with 5V/85mA output
capability.
If EN is switched to low while TXD is still high, the device is forced to silent mode. No data transmission is then possible, and
the current consumption is reduced to IVS typ. 57µA. The VCC regulator has its full functionality.
If EN is switched to low while TXD is low, the device is forced to sleep mode. No data transmission is possible, and the
voltage regulator is switched off.
3.3.11 Wake Input Pin (WAKE)
The wake input pin is a high-voltage input used to wake up the device from sleep mode or silent mode. It is usually
connected to an external switch in the application to generate a local wake-up. A pull-up current source, typically 10µA, is
implemented.
If a local wake-up is not needed for the application, connect the Wake pin directly to the VS pin.
3.3.12 Mode Input Pin (MODE)
Connect the MODE pin directly or via an external resistor to GND for normal watchdog operation. To debug the software of
the connected microcontroller, connect the MODE pin to VCC and the watchdog is switched off.
3.3.13 TM Input Pin
The TM pin is used for final production measurements at Atmel®. In normal application, it has to be always connected to
GND.
3.3.14 KL_15 Pin
The KL_15 pin is a high-voltage input used to wake up the device from sleep or silent mode. It is an edge sensitive pin
(low-to-high transition). It is usually connected to ignition to generate a local wake-up in the application when the ignition is
switched on. Although KL_15 pin is at high voltage (VBatt), it is possible to switch the IC into sleep or silent mode. Connect
the KL_15 pin directly to GND if you do not need it. A debounce timer with a typical TdbKl_15 of 160µs is implemented.
The input voltage threshold can be adjusted by varying the external resistor due to the input current IKL_15. To protect this pin
against voltage transients, a serial resistor of 47kΩ and a ceramic capacitor of 100nF are recommended. With this RC
combination you can increase the wake-up time TwKL_15 and, therefore, the sensitivity against transients on the ignition
Kl.15.
The wake-up time can also be increased by using external capacitors with higher values.
3.3.15 INH Output Pin
The INH Output pin is used to switch on an external voltage regulator during normal or fail-safe mode. The INH pin is
switched off in sleep or silent mode. It is possible to switch off the external 1kΩ master resistor via the INH pin for master
node applications. The INH pin is switched off during VCC under voltage reset.
3.3.16 Reset Output Pin (NRES)
The reset output pin, an open drain output, switches to low during VCC under voltage or a watchdog failure.
3.3.17 WD_OSC Output Pin
The WD_OSC output pin provides a typical voltage of 1.2V, which supplies an external resistor with values between 34kΩ
and 120kΩ to adjust the watchdog oscillator time.
3.3.18 NTRIG Input Pin
The NTRIG input pin is the trigger input for the window watchdog. A pull-up resistor is implemented. A negative edge triggers
the watchdog. The trigger signal (low) must exceed a minimum time ttrigmin to generate a watchdog trigger.
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3.3.19 Wake-up Events from Sleep or Silent Mode
●LIN-bus
●WAKE pin
●EN pin
●KL_15
3.3.20 Modes of Operation
Figure 3-2. Modes of Operation
3.3.20.1 Normal Mode
This is the normal transmitting and receiving mode at the LIN interface in accordance with the LIN specification LIN 2.x. The
voltage regulator is active and can source up to 85mA. The under voltage detection is activated. The watchdog needs a
trigger signal from NTRIG to avoid resets at NRES. If NRES is switched to low, the IC changes its state to fail-safe mode.
Table 3-1. Table of Modes
Mode of Operation Transceiver VCC Watchdog WD_OSC INH RXD LIN
Fail-safe Off 5V On 1.23V On High,
except after wake-up Recessive
Normal On 5V On 1.23V On LIN depending TXD
depending
Silent Off 5V Off 0V Off High Recessive
Sleep Off 0V Off 0V Off 0V Recessive
Unpowered Mode
VBatt = 0V
a: VS > 5V
b: VS < 4V
c: Bus wake-up event
d: Wake up from WAKE or KL_15 pin
Sleep Mode
VCC: switched off
Communication: OFF
Watchdog: OFF
Go to silent command
a
TXD = 0
EN = 0
TXD = 1
EN = 0
EN = 1
EN = 1
EN = 1
b
b
b
c + d + e
e
c + d
b
Local wake-up event
Go to sleep command
e: NRES switches to low
Silent Mode
VCC: 5V/85mA
With undervoltage monitoring
Communication: OFF
Watchdog: OFF
Normal Mode
VCC: 5V/85mA
With undervoltage
monitoring
Communication: ON
Watchdog: ON
Fail-safe Mode
VCC: 5V/85mA
With undervoltage monitoring
Communication: OFF
Watchdog: ON
ATA6612C/ATA6613C [DATASHEET]
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3.3.20.2 Silent Mode
A falling edge at EN when TXD is high switches the IC into silent mode. The TXD signal has to be logic high during the mode
select window (see Figure 3-3). The transmission path is disabled in silent mode. The overall supply current from VBatt is a
combination of the IVSsi 57µA plus the VCC regulator output current IVCC.
The internal slave termination between the LIN pin and the VS pin is disabled in silent mode, only a weak pull-up current
(typically 10µA) between the LIN pin and the VS pin is present. silent mode can be activated independently from the actual
level on the LIN, WAKE, or KL_15 pins.
If an under voltage condition occurs, NRES is switched to low, and the IC changes its state to fail-safe mode.
A voltage lower than the LIN pre_wake detection VLINL at the LIN pin activates the internal LIN receiver and switches on the
internal slave termination between the LIN pin and the VS pin.
Figure 3-3. Switch to Silent Mode
Delay time silent mode
td_sleep = maximum 20μs
Mode select window
LIN switches directly to recessive mode
td = 3.2μs
LIN
VCC
NRES
TXD
EN
Normal Mode Silent Mode
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A falling edge at the LIN pin followed by a dominant bus level maintained for a certain time period (> tbus) and followed by a
rising edge at the LIN pin (see Figure 3-4) result in a remote wake-up request. The device switches from silent mode to
fail-safe mode. The remote wake-up request is indicated by a low level at the RXD pin to interrupt the microcontroller (see
Figure 3-4). EN high can be used to switch directly to normal mode.
Figure 3-4. LIN Wake-up from Silent Mode
Watchdog off Start watchdog lead time td
Watchdog
Undervoltage detection active
Silent mode 5V Fail safe mode 5V Normal mode
Low
Fail-safe mode Normal mode
EN High
Node in silent mode
HighHigh
NRES
EN
VCC
Voltage
Regulator
RXD
LIN Bus
Bus wake-up filtering time
tbus
TXD
ATA6612C/ATA6613C [DATASHEET]
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3.3.20.3 Sleep Mode
A falling edge at EN when TXD is low switches the IC into sleep mode. The TXD signal has to be logic low during the mode
select window (Figure 3-5). In order to avoid any influence to the LIN-pin during switching into sleep mode it is possible to
switch the EN up to 3.2µs earlier to LOW than the TXD. Therefore, the best and easiest way are two falling edges at TXD
and EN at the same time.The transmission path is disabled in sleep mode. The supply current IVSsleep from VBatt is typically
10µA.
The VCC regulator and the INH output are switched off. NRES and RXD are low. The internal slave termination between the
LIN pin and VS pin is disabled, only a weak pull-up current (typically 10µA) between the LIN pin and the VS pin is present.
sleep mode can be activated independently from the current level on the LIN, WAKE, or KL_15 pin.
A voltage lower than the LIN pre_wake detection VLINL at the LIN pin activates the internal LIN receiver and switches on the
internal slave termination between the LIN pin and the VS pin.
A falling edge at the LIN pin followed by a dominant bus level maintained for a certain time period (> tbus) and followed by a
rising edge at pin LIN results in a remote wake-up request. The device switches from sleep mode to fail-safe mode.
The VCC regulator is activated, and the remote wake-up request is indicated by a low level at the RXD pin to interrupt the
microcontroller (see Figure 3-6 on page 15).
EN high can be used to switch directly from sleep/silent to fail-safe mode. If EN is still high after VCC ramp up and under
voltage reset time, the IC switches to the normal mode.
Figure 3-5. Switch to Sleep Mode
3.3.20.4 Fail-safe Mode
The device automatically switches to fail-safe mode at system power-up and the voltage regulator is switched on
(see Figure 3-7 on page 17). The NRES output switches to low for tres = 4ms and gives a reset to the microcontroller. LIN
communication is switched off. The IC stays in this mode until EN is switched to high. The IC then changes to normal mode.
A power down of VBatt (VS< 4V) during silent or sleep mode switches the IC into fail-safe mode. A low at NRES switches into
fail-safe mode directly. During fail-safe mode the TXD pin is an output and signals the last wake-up source.
Delay time sleep mode
td_sleep = maximum 20μs
LIN switches directly to recessive mode
td = 3.2μs
LIN
VCC
NRES
TXD
EN
Sleep Mode
Normal Mode
Mode select window
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3.3.20.5 Unpowered Mode
If you connect battery voltage to the application circuit, the voltage at the VS pin increases according to the block capacitor
(see Figure 3-7 on page 17). After VS is higher than the VS undervoltage threshold VSth, the IC mode changes from
unpowered mode to fail-safe mode. The VCC output voltage reaches its nominal value after tVCC. This time, tVCC, depends
on the VCC capacitor and the load.
The NRES is low for the reset time delay treset. During this time, treset, no mode change is possible.
Figure 3-6. LIN Wake-up from Sleep Mode
3.3.21 Wake-up Scenarios from Silent to Sleep Mode
3.3.21.1 Remote Wake-up via Dominant Bus State
A voltage lower than the LIN pre_wake detection VLINL at the LIN pin activates the internal LIN receiver.
A falling edge at the LIN pin followed by a dominant bus level VBUSdom maintained for a certain time period (> tBUS) and
followed by a rising edge at pin LIN result in a remote wake-up request. The device switches from silent or sleep mode to
fail-safe mode. The VCC voltage regulator is/remains activated, the INH pin is switched to high, and remote wake-up request
is indicated by a low level at the RXD pin to generate an interrupt for the microcontroller. A low level at the LIN pin in the
normal mode starts the bus wake-up filtering time, and if the IC is switched to silent or sleep mode, it will receive a wake-up
after a positive edge at the LIN pin.
Regulator wake-up time
Off state
On state
Low
Fail-safe Mode Normal Mode
EN High
Microcontroller
start-up time delay
Reset
time
Watchdog
NRES
EN
VCC
Voltage
Regulator
RXD
LIN Bus
Bus wake-up filtering time
tbus
TXD
Watchdog off Start watchdog lead time td
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
16
3.3.21.2 Local Wake-up via Pin Wake
A falling edge at the WAKE pin followed by a low level maintained for a certain time period (> tWAKE) results in a local
wake-up request. The device switches to fail-safe mode. The local wake-up request is indicated by a low level at the RXD
pin to generate an interrupt in the microcontroller and a strong pull down at TXD. When the wake pin is low, it is possible to
switch to silent or sleep mode via pin EN. In this case, the wake-up signal has to be switched to high >10µs before the
negative edge at WAKE starts a new local wake-up request.
3.3.21.3 Local Wake-up via Pin KL_15
A positive edge at pin KL_15 followed by a high voltage level for a certain time period (>tKL_15) results in a local wake-up
request. The device switches into the fail-safe mode. The extra long wake-up time ensures that no transients at KL_15
create a wake up. The local wake-up request is indicated by a low level at the RXD pin to generate an interrupt for the
microcontroller and a strong pull down at TXD. During high-level voltage at pin KL_15, it is possible to switch to silent or
sleep mode via pin EN. In this case, the wake-up signal has to be switched to low >250µs before the positive edge at KL_15
starts a new local wake-up request. With external RC combination, the time is even longer.
3.3.21.4 Wake-up Source Recognition
The device can distinguish between a local wake-up request (Wake or KL_15 pins) and a remote wake-up request (via LIN
bus). The wake-up source can be read on the TXD pin in fail-safe mode. A high level indicates a remote wake-up request
(weak pull up at the TXD pin); a low level indicates a local wake-up request (strong pull down at the TXD pin). The wake-up
request flag (signalled on the RXD pin), as well as the wake-up source flag (signalled on the TXD pin), is immediately reset if
the microcontroller sets the EN pin to high (see Figure 3-3 on page 12 and Figure 3-4 on page 13) and the IC is in normal
mode. The last wake-up source flag is stored and signalled in fail-safe mode at the TXD pin.
3.3.22 Fail-safe Features
●During a short-circuit at LIN to VBattery, the output limits the output current to IBUS_LIM. Due to the power dissipation, the
chip temperature exceeds TLINoff, and the LIN output is switched off. The chip cools down and after a hysteresis of
Thys, switches the output on again. RXD stays on high because LIN is high. During LIN over temperature switch-off,
the VCC regulator works independently.
●During a short-circuit from LIN to GND the IC can be switched into sleep or silent mode. If the short-circuit disappears,
the IC starts with a remote wake-up.
●The reverse current is very low <15µA at the LIN pin during loss of VBatt or GND. This is optimal behavior for bus
systems where some slave nodes are supplied from battery or ignition.
●During a short circuit at VCC, the output limits the output current to IVCCn. Because of under voltage, NRES switches
to low and sends a reset to the microcontroller. The IC switches into fail-safe mode. If the chip temperature exceeds
the value TVCCoff, the VCC output switches off. The chip cools down and after a hysteresis of Thys, switches the output
on again. Because of the fail-safe mode, the VCC voltage will switch on again although EN is switched off from the
microcontroller. The microcontroller can start with its normal operation.
●EN pin provides a pull-down resistor to force the transceiver into recessive mode if EN is disconnected.
●RXD pin is set floating if VBatt is disconnected.
●TXD pin provides a pull-up resistor to force the transceiver into recessive mode if TXD is disconnected.
●If TXD is short-circuited to GND, it is possible to switch to sleep mode via ENABLE after tdom >20ms.
●If the WD_OSC pin has a short-circuit to GND and the NTRIG signal has a period time >27ms, the watchdog runs with
an internal oscillator and guarantees a reset after the second NTRIG signal at the latest.
●If the resistor at WO_OSC pin is disconnected, the watchdog runs with an internal oscillator and guarantees a reset
after the second NTRIG signal at the latest.
17
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
3.3.23 Voltage Regulator
The voltage regulator needs an external capacitor for compensation and for smoothing the disturbances from the
microcontroller. It is recommended to use an electrolytic capacitor with C ≥ 1.8µF and a ceramic capacitor with C = 100nF.
The values of these capacitors can be varied by the customer, depending on the application.
The main power dissipation of the IC is created from the VCC output current IVCC, which is needed for the application. In
Figure 3-8 the safe operating area is shown.
Figure 3-7. VCC Voltage Regulator: Ramp Up and Undervoltage Detection
Figure 3-8. Power Dissipation: Safe Operating Area VCC Output Current versus Supply Voltage VS at Different
Ambient Temperatures
For programming purposes of the microcontroller it is potentially necessary to supply the VCC output via an external power
supply while the VS pin of the system basis chip is disconnected. This will not affect the system basis chip.
NRES
5V
t
t
t
VS
VCC
5V
Vthun
tres_f
tReset
tVCC
5.5V
12V
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
90
80
70
60
50
40
30
20
10
0
IVCC (mA)
VS (V)
Tamb = 100°C
Tamb = 105°C
Tamb = 110°C
Tamb = 115°C
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
18
3.3.24 Watchdog
The watchdog anticipates a trigger signal from the microcontroller at the NTRIG (negative edge) input within a time window
of Twd. The trigger signal must exceed a minimum time ttrigmin > 200ns. If a triggering signal is not received, a reset signal will
be generated at output NRES. After a watchdog reset the IC starts with the lead time. The timing basis of the watchdog is
provided by the internal oscillator. Its time period, Tosc, is adjustable via the external resistor Rwd_osc (34kΩ to 120kΩ).
During silent or sleep mode the watchdog is switched off to reduce current consumption.
The minimum time for the first watchdog pulse is required after the under voltage reset at NRES disappears. It is defined as
lead time td. After wake up from sleep or silent mode, the lead time td starts with the negative edge of the RXD output.
3.3.24.1 Typical Timing Sequence with RWD_OSC = 51k
Ω
The trigger signal Twd is adjustable between 20ms and 64ms using the external resistor RWD_OSC.
For example, with an external resistor of RWD_OSC = 51kΩ ±1%, the typical parameters of the watchdog are as follows:
tosc = 0.405 × RWD_OSC – 0.0004 × (RWD_OSC)2 (RWD_OSC in kΩ; tosc in µs)
tOSC = 19.6µs due to 51kΩ
td = 7895 × 19.6µs = 155ms
t1 = 1053 × 19.6µs = 20.6ms
t2 = 1105 × 19.6µs = 21.6ms
tnres = constant = 4ms
After ramping up the battery voltage, the 5V regulator is switched on. The reset output NRES stays low for the time treset
(typically 4ms), then it switches to high, and the watchdog waits for the trigger sequence from the microcontroller. The lead
time, td, follows the reset and is td = 155ms. In this time, the first watchdog pulse from the microcontroller is required. If the
trigger pulse NTRIG occurs during this time, the time t1 starts immediately. If no trigger signal occurs during the time td, a
watchdog reset with tNRES = 4ms will reset the microcontroller after td= 155ms. The times t1 and t2 have a fixed relationship
between each other. A triggering signal from the microcontroller is anticipated within the time frame of t2= 21.6ms. To avoid
false triggering from glitches, the trigger pulse must be longer than tTRIG,min > 200ns. This slope serves to restart the
watchdog sequence. If the triggering signal fails in this open window t2, the NRES output will be drawn to ground. A
triggering signal during the closed window t1 immediately switches NRES to low.
Figure 3-9. Timing Sequence with RWD_OSC = 51kΩ
tnres = 4ms
Undervoltage Reset Watchdog Reset
treset = 4ms
ttrig > 200ns
t1 = 20.6ms t2 = 21ms
t2
t1
twd
td = 155ms
VCC
NTRIG
NRES
19
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
3.3.24.2 Worst Case Calculation with RWO_OSC = 51kΩ
The internal oscillator has a tolerance of 20%. This means that t1 and t2 can also vary by 20%. The worst case calculation for
the watchdog period twd is calculated as follows.
The ideal watchdog time twd is between the maximum t1 and the minimum t1 plus the minimum t2.
t1,min = 0.8 × t1 = 16.5ms, t1,max = 1.2 × t1 = 24.8ms
t2,min = 0.8 × t2 = 17.3ms, t2,max = 1.2 × t2 = 26ms
twdmax = t1min + t2min = 16.5ms + 17.3ms = 33.8ms
twdmin = t1max = 24.8ms
twd = 29.3ms ±4.5ms (±15%)
A microcontroller with an oscillator tolerance of ±15% is sufficient to supply the trigger inputs correctly.
Table 3-2. Typical Watchdog Timings
RWD_OSC
kΩ
Oscillator
Period
tosc/µs
Lead
Time
td/ms
Closed
Window
t1/ms
Open Window
t2/ms
Trigger Period from
Microcontroller twd/ms
Reset Time
tnres/ms
34 13.3 105 14.0 14.7 19.9 4
51 19.61 154.8 20.64 21.67 29.32 4
91 33.54 264.80 35.32 37.06 50.14 4
120 42.84 338.22 45.11 47.34 64.05 4
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
20
4. Electrical Characteristics
5V < VS < 27V, –40°C < Tcase < 125°C, –40°C < Tj < 150°C, unless otherwise specified. All values refer to GND pins
No. Parameters Test Conditions Pin Symbol Min. Typ. Max. Unit Type*
1VS Pin
1.1 Nominal DC voltage
range VS VS527 V A
1.2 Supply current in sleep
mode
Sleep mode
VLIN > VS – 0.5V
VS < 14V (Tj = 25°C)
VS IVSsleep 310 14 µA B
Sleep mode
VLIN > VS – 0.5V
VS < 14V (Tj = 125°C)
VS IVSsleep 511 16 µA A
1.3 Supply current in silent
mode
Bus recessive
VS < 14V (Tj = 25°C)
Without load at VCC
VS IVSsi 47 57 67 µA B
Bus recessive
VS < 14V (Tj = 125°C)
Without load at VCC
VS IVSsi 56 66 76 µA A
1.4 Supply current in normal
mode
Bus recessive
VS < 14V
Without load at VCC
VS IVSrec 0.3 0.8 mA A
1.5 Supply current in normal
mode
Bus dominant
VS < 14V
VCC load current 50mA
VS IVSdom 50 53 mA A
1.6 Supply current in
fail-safe mode
Bus recessive
VS < 14V
Without load at VCC
VS IVSfail 250 550 µA A
1.7 VS undervoltage
threshold VS VSth 3.7 4.4 5 V A
1.8 VS undervoltage
threshold hysteresis VS VSth_hys 0.2 V A
2RXD Output Pin
2.1 Low-level output sink
current
Normal mode
VLIN =0V
VRXD =0.4V
RXD IRXD 1.3 2.5 8mA A
2.2 Low-level output voltage IRXD = 1mA RXD VRXDL 0.4 V A
2.3 Internal resistor to VCC RXD RRXD 3 5 7 kΩA
3TXD Input/Output Pin
3.1 Low-level voltage input TXD VTXDL –0.3 +0.8 V A
3.2 High-level voltage input TXD VTXDH 2VCC +
0.3V V A
3.3 Pull-up resistor VTXD =0V TXD RTXD 125 250 400 kΩA
3.4 High-level leakage
current VTXD =VCC TXD ITXD –3 +3 µA A
3.5
Low-level output sink
current at local wake-up
request
Fail-safe mode
VLIN = VS
VWAKE = 0V
VTXD = 0.4V
TXD ITXDwake 22.5 8mA A
*) Type means: A = 100% tested, B = 100% correlation tested, C = Characterized on samples, D = Design parameter
21
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
4EN Input Pin
4.1 Low-level voltage input EN VENL –0.3 +0.8 V A
4.2 High-level voltage input EN VENH 2VCC +
0.3V V A
4.3 Pull-down resistor VEN = VCC EN REN 50 125 200 kΩA
4.4 Low-level input current VEN = 0V EN IEN –3 +3 µA A
5NTRIG Watchdog Input Pin
5.1 Low-level voltage input NTRIG VNTRIGL –0.3 +0.8 V A
5.2 High-level voltage input NTRIG VNTRIGH 2VCC +
0.3V V A
5.3 Pull-up resistor VNTRIG = 0V NTRIG RNTRIG 125 250 400 kΩA
5.4 High-level leakage
current VNTRIG = VCC NTRIG INTRIG –3 +3 µA A
6Mode Input Pin
6.1 Low-level voltage input MODE VMODEL –0.3 +0.8 V A
6.2 High-level voltage input MODE VMODEH 2VCC +
0.3V V A
6.3 High-level leakage
current
VMODE = VCC or
VMODE = 0V MODE IMODE –3 +3 µA A
7INH Output Pin
7.1 High-level voltage IINH = –15mA INH VINHH VS – 0.75 VSV A
7.2 Switch-on resistance
between VS and INH INH RINH 30 50 ΩA
7.3 Leakage current Sleep mode
VINH = 0V/27V, VS = 27V INH IINHL –3 +3 µA A
8
LIN Bus Driver: Bus Load Conditions:
Load 1 (small): 1nF, 1kΩ; Load 2 (large): 10nF, 500Ω; Internal pull-up RRXD = 5kΩ; CRXD = 20pF
Load 3 (medium): 6.8nF, 660Ω, characterized on samples
10.6 and 10.7 specifies the timing parameters for proper operation at 20kBit/s and 10.8 and 10.9 at 10.4kBit/s
8.1 Driver recessive output
voltage Load1/load2 LIN VBUSrec 0.9 × VSVSV A
8.2 Driver dominant voltage VVS = 7V
Rload = 500ΩLIN V_LoSUP 1.2 V A
8.3 Driver dominant voltage VVS = 18V
Rload = 500ΩLIN V_HiSUP 2 V A
8.4 Driver dominant voltage VVS = 7.0V
Rload = 1000ΩLIN V_LoSUP_1k 0.6 V A
8.5 Driver dominant voltage VVS = 18V
Rload = 1000Ω LIN V_HiSUP_1k 0.8 V A
8.6 Pull-up resistor to VS
The serial diode is
mandatory LIN RLIN 20 30 60 kΩA
8.7 Voltage drop at the
serial diodes
In pull-up path with Rslave
ISerDiode = 10mA LIN VSerDiode 0.4 1.0 V D
4. Electrical Characteristics (Continued)
5V < VS < 27V, –40°C < Tcase < 125°C, –40°C < Tj < 150°C, unless otherwise specified. All values refer to GND pins
No. Parameters Test Conditions Pin Symbol Min. Typ. Max. Unit Type*
*) Type means: A = 100% tested, B = 100% correlation tested, C = Characterized on samples, D = Design parameter
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
22
8.8 LIN current limitation
VBUS = VBatt_max LIN IBUS_LIM 40 120 200 mA A
8.9
Input leakage current at
the receiver including
pull-up resistor as
specified
Input leakage current
Driver off
VBUS = 0V
VBatt = 12V
LIN IBUS_PAS_do
m
–1 –0.35 mA A
8.10 Leakage current LIN
recessive
Driver off
8V < VBatt < 18V
8V < VBUS < 18V
VBUS ≥ VBatt
LIN IBUS_PAS_re
c
10 20 µA A
8.11
Leakage current when
control unit
disconnected from
ground.
Loss of local ground
must not affect
communication in the
residual network.
GNDDevice = VS
VBatt = 12V
0V < VBUS < 18V
LIN IBUS_NO_gn
d
–10 +0.5 +10 µA A
8.12
Leakage current at a
disconnected battery.
Node has to sustain the
current that can flow
under this condition.
Bus must remain
operational under this
condition.
VBatt disconnected
VSUP_Device = GND
0V < VBUS < 18V
LIN IBUS_NO_bat 0.1 2µA A
9LIN Bus Receiver
9.1 Center of receiver
threshold
VBUS_CNT =
(Vth_dom + Vth_rec)/2 LIN VBUS_CNT
0.475 ×
VS
0.5 ×
VS
0.525 ×
VS
V A
9.2 Receiver dominant state VEN = 5V LIN VBUSdom 0.4 × VSV A
9.3 Receiver recessive
state VEN = 5V LIN VBUSrec 0.6 × VSV A
9.4 Receiver input
hysteresis Vhys = Vth_rec – Vth_dom LIN VBUShys
0.028 ×
VS
0.1 × VS
0.175 ×
VS
V A
9.5 Pre_Wake detection LIN
High-level input voltage LIN VLINH VS – 2V VS +
0.3V V A
9.6 Pre_Wake detection LIN
Low-level input voltage Activates the LIN receiver LIN VLINL –27 VS –
3.3V V A
4. Electrical Characteristics (Continued)
5V < VS < 27V, –40°C < Tcase < 125°C, –40°C < Tj < 150°C, unless otherwise specified. All values refer to GND pins
No. Parameters Test Conditions Pin Symbol Min. Typ. Max. Unit Type*
*) Type means: A = 100% tested, B = 100% correlation tested, C = Characterized on samples, D = Design parameter
23
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
10 Internal Timers
10.1 Dominant time for wake-
up via LIN bus VLIN = 0V LIN tbus 30 90 150 µs A
10.2
Time delay for mode
change from fail-safe
into normal mode via
EN pin
VEN = 5V EN tnorm 515 20 µs A
10.3
Time delay for mode
change from normal
mode to sleep mode via
EN pin
VEN = 0V EN tsleep 2 7 12 µs A
10.4 TXD dominant time-out
time VTXD = 0V TXD tdom 613 20 ms A
10.5
Time delay for mode
change from silent
mode into normal mode
via EN
VEN = 5V EN ts_n 515 40 µs A
10.6 Duty cycle 1
THRec(max) = 0.744 × VS
THDom(max) = 0.581 × VS
VS = 7.0V to 18V
tBit = 50µs
D1 = tbus_rec(min)/(2 × tBit)
LIN D1 0.396 A
10.7 Duty cycle 2
THRec(min) = 0.422 × VS
THDom(min) = 0.284 × VS
VS = 7.6V to 18V
tBit = 50µs
D2 = tbus_rec(max)/(2 × tBit)
LIN D2 0.581 A
10.8 Duty cycle 3
THRec(max) = 0.778 × VS
THDom(max) = 0.616 × VS
VS = 7.0V to 18V
tBit = 96µs
D3 = tbus_rec(min)/(2 × tBit)
LIN D3 0.417 A
10.9 Duty cycle 4
THRec(min) = 0.389 × VS
THDom(min) = 0.251 × VS
VS = 7.6V to 18V
tBit = 96µs
D4 = tbus_rec(max)/(2 × tBit)
LIN D4 0.590 A
10.10 Slope time falling and
rising edge at LIN VS = 7.0V to 18V LIN tSLOPE_fall
tSLOPE_rise
3.5 22.5 µs A
11 Receiver Electrical AC Parameters of the LIN Physical Layer
LIN Receiver, RXD Load Conditions (CRXD): 20pF
11.1
Propagation delay of
receiver (Figure 4-1 on
page 26)
VS = 7.0V to 18V
trx_pd = max(trx_pdr, trx_pdf)RXD trx_pd 6µs A
11.2
Symmetry of receiver
propagation delay rising
edge minus falling edge
VS = 7.0V to 18V
trx_sym = trx_pdr – trx_pdf
RXD trx_sym –2 +2 µs A
4. Electrical Characteristics (Continued)
5V < VS < 27V, –40°C < Tcase < 125°C, –40°C < Tj < 150°C, unless otherwise specified. All values refer to GND pins
No. Parameters Test Conditions Pin Symbol Min. Typ. Max. Unit Type*
*) Type means: A = 100% tested, B = 100% correlation tested, C = Characterized on samples, D = Design parameter
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
24
12 NRES Open Drain Output Pin
12.1 Low-level output voltage VS ≥ 5.5V
INRES = 1mA NRES VNRESL 0.14 V A
12.2 Low-level output low 10kΩ to 5V
VCC = 0V NRES VNRESLL 0.14 V A
12.3 Undervoltage reset time VS≥ 5.5V
CNRES = 20pF NRES treset 2 4 6 ms A
12.4 Reset debounce time
for falling edge
VS≥ 5.5V
CNRES = 20pF NRES tres_f 1.5 10 µs A
13 Watchdog Oscillator
13.1 Voltage at WD_OSC in
normal mode
IWD_OSC = –200µA
VVS ≥ 4V WD_OSC VWD_OSC 1.13 1.23 1.33 V A
13.2 Possible values of
resistor WD_OSC ROSC 34 120 kΩA
13.3 Oscillator period ROSC = 34kΩtOSC 10.65 13.3 15.97 µs A
13.4 Oscillator period ROSC = 51kΩtOSC 15.68 19.6 23.52 µs A
13.5 Oscillator period ROSC = 91kΩtOSC 26.83 33.5 40.24 µs A
13.6 Oscillator period ROSC = 120kΩtOSC 34.2 42.8 51.4 µs A
14 Watchdog Timing Relative to tOSC
14.1 Watchdog lead time
after reset td7895 cycles A
14.2 Watchdog closed
window t11053 cycles A
14.3 Watchdog open window t21105 cycles A
14.4 Watchdog reset time
NRES NRES tnres 3.2 44.8 ms A
15 KL_15 Pin
15.1 High-level input voltage
RV = 47 kΩPositive edge initializes a
wake-up KL_15 VKL_15H 4VS +
0.3V V A
15.2 Low-level input voltage
RV = 47 kΩKL_15 VKL_15L –1 +2 V A
15.3 KL_15 pull-down
current
VS < 27V
VKL_15 = 27V KL_15 IKL_15 50 65 µA A
15.4 Internal debounce time Without external capacitor KL_15 TdbKL_15 80 160 250 µs A
15.5 KL_15 wake-up time RV = 47kΩ, C = 100nF KL_15 TwKL_15 0.4 24.5 ms C
16 WAKE Pin
16.1 High-level input voltage WAKE VWAKEH VS – 1V VS +
0.3V V A
16.2 Low-level input voltage Initializes a wake-up signal WAKE VWAKEL –1 VS –
3.3V V A
16.3 WAKE pull-up current VS < 27V
VWAKE = 0V WAKE IWAKE –30 –10 µA A
16.4 High-level leakage
current
VS = 27V
VWAKE = 27V WAKE IWAKEL –5 +5 µA A
4. Electrical Characteristics (Continued)
5V < VS < 27V, –40°C < Tcase < 125°C, –40°C < Tj < 150°C, unless otherwise specified. All values refer to GND pins
No. Parameters Test Conditions Pin Symbol Min. Typ. Max. Unit Type*
*) Type means: A = 100% tested, B = 100% correlation tested, C = Characterized on samples, D = Design parameter
25
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
16.5 Time of low pulse for
wake-up via WAKE pin VWAKE = 0V WAKE IWAKEL 30 70 150 µs A
17 VCC Voltage Regulator, PVCC = VCC
17.1 Output voltage VCC
5.5V < VS < 18V
(0mA to 50mA) VCC VCCnor 4.9 5.1 V A
6V < VS < 18V
(0mA to 85mA) VCC VCCnor 4.9 5.1 V C
17.2 Output voltage VCC at
low VS 4V < VS < 5.5V VCC VCClow VS – VD5.1 V A
17.3 Regulator drop voltage VS > 4V
IVCC = –20mA VS, VCC VD1 250 mV A
17.4 Regulator drop voltage VS > 4V
IVCC = –50mA VS, VCC VD2 400 600 mV A
17.5 Regulator drop voltage VS > 3.3V
IVCC = –15mA VS, VCC VD3 200 mV A
17.6 Line regulation 5.5V < VS < 18V VCC VCCline 0.1 0.2 % A
17.7 Load regulation 5mA < IVCC < 50mA VCC VCCload 0.1 0.5 % A
17.8 Power supply ripple
rejection
10Hz to 100kHz
CVCC = 10µF
VS = 14V, IVCC = –15mA
VCC 50 dB D
17.9 Output current limitation VS > 5.5V VCC IVCClim –240 –130 –85 mA A
17.10 External load capacity
0.2Ω < ESR < 5Ω at
100kHz
for phase margin ≥ 60° VCC Cload 1.8 10 µF D
ESR < 0.2Ω at 100kHz
for phase margin ≥ 30°
17.11 VCC undervoltage
threshold
Referred to VCC
VS > 5.5V VCC VthunN 4.2 4.8 V A
17.12 Hysteresis of
undervoltage threshold
Referred to VCC
VS > 5.5V VCC Vhysthun 250 mV A
17.13 Ramp-up time VS >
5.5V to VCC = 5V
CVCC = 2.2µF
Iload = –5mA at VCC VCC tVCC 130 300 µs A
4. Electrical Characteristics (Continued)
5V < VS < 27V, –40°C < Tcase < 125°C, –40°C < Tj < 150°C, unless otherwise specified. All values refer to GND pins
No. Parameters Test Conditions Pin Symbol Min. Typ. Max. Unit Type*
*) Type means: A = 100% tested, B = 100% correlation tested, C = Characterized on samples, D = Design parameter
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
26
Figure 4-1. Definition of Bus Timing Parameters
TXD
(Input to transmitting node)
VS
(Transceiver supply
of transmitting node)
RXD
(Output of receiving node1)
RXD
(Output of receiving node2)
LIN Bus Signal
Thresholds of
receiving node1
Thresholds of
receiving node2
tBus_rec(max)
trx_pdr(1)
trx_pdf(2)
trx_pdr(2)
trx_pdf(1)
tBus_dom(min)
tBus_dom(max)
THRec(max)
THDom(max)
THRec(min)
THDom(min)
tBus_rec(min)
tBit tBit
tBit
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5. Microcontroller Block
5.1 Features
●High performance, low power Atmel® AVR® 8-bit microcontroller
●Advanced RISC architecture
●131 powerful instructions - most single clock cycle execution
●32 × 8 general purpose working register
●Fully static operation
●Up to 16MIPS throughput at 16MHz
●On-chip 2-cycle multiplier
●Non-volatile program and data memories
●8/16Kbytes of in-system self-programmable flash (Atmel ATA6612C/ATA6613C)
Endurance: 75,000 write/erase cycles
●Optional boot code section with independent lock bits
In-system programming by on-chip boot program
True read-while-write operation
●512bytes EEPROM
Endurance: 100,000 write/erase cycles
●1Kbyte internal SRAM
●Programming lock for software security
●Peripheral features
●Two 8-bit Timer/Counters with separate prescaler and compare mode
●One 16-bit Timer/Counter with separate prescaler, compare mode, and capture mode
●Real time counter with separate oscillator
●Six PWM channels
●8-channel 10-bit ADC
●Programmable serial USART
●Master/slave SPI serial interface
●Byte-oriented 2-wire serial interface
●Programmable watchdog timer with separate on-chip oscillator
●On-chip analog comparator
●Interrupt and wake-up on pin change
●Special microcontroller features
●Power-on reset and programmable brown-out detection
●Internal calibrated oscillator
●External and internal interrupt sources
●Five sleep modes: idle, ADC noise reduction, power-save, power-down, and standby
●I/O
●23 programmable I/O lines
●Operating voltage
●2.7V to 5.5V
●Speed grade
●0 to 8MHz at 2.7V to 5.5V, 0 to 16MHz at 4.5V to 5.5V
●Low power consumption
●Active mode:
●4MHz, 3.0V: 1.8mA
●Power-down mode:
●5µA at 3.0V
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5.2 Overview
The Atmel® ATA6612C/ATA6613C uses a low-power CMOS 8-bit microcontroller based on the Atmel AVR® enhanced RISC
architecture. By executing powerful instructions in a single clock cycle, the Atmel ATA6612C/ATA6613C achieves
throughputs approaching 1MIPS per MHz allowing the system designer to optimize power consumption versus processing
speed.
5.2.1 Block Diagram
Figure 5-1. Block Diagram
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The Atmel® AVR® core combines a rich instruction set with 32 general purpose working registers. All the 32 registers are
directly connected to the arithmetic logic unit (ALU), allowing two independent registers to be accessed in one single
instruction executed in one clock cycle. The resulting architecture is more code efficient while achieving throughputs up to
ten times faster than conventional CISC microcontrollers.
The Atmel ATA6612C/ATA6613C provides the following features: 8K/16K bytes of in-system programmable flash with
read-while-write capabilities, 512 bytes EEPROM, 1Kbyte SRAM, 23 general purpose I/O lines, 32 general purpose working
registers, three flexible Timer/Counters with compare modes, internal and external interrupts, a serial programmable
USART, a byte-oriented 2-wire serial interface, an SPI serial port, a 6-channel 10-bit ADC (8 channels in TQFP and QFN
packages), a programmable watchdog timer with internal oscillator, and five software selectable power saving modes. The
idle mode stops the CPU while allowing the SRAM, Timer/Counters, USART, 2-wire serial interface, SPI port, and interrupt
system to continue functioning. The power-down mode saves the register contents but freezes the oscillator, disabling all
other chip functions until the next interrupt or hardware reset. In power-save mode, the asynchronous timer continues to run,
allowing the user to maintain a timer base while the rest of the device is sleeping. The ADC noise reduction mode stops the
CPU and all I/O modules except asynchronous timer and ADC, to minimize switching noise during ADC conversions. In
standby mode, the crystal/resonator oscillator is running while the rest of the device is sleeping. This allows very fast start-up
combined with low power consumption.
The device is manufactured using Atmel’s high density non-volatile memory technology. The on-chip ISP flash allows the
program memory to be reprogrammed in-system through an SPI serial interface, by a conventional non-volatile memory
programmer, or by an on-chip boot program running on the Atmel AVR core. The boot program can use any interface to
download the application program in the Application Flash memory. Software in the Boot Flash section will continue to run
while the application flash section is updated, providing true read-while-write operation. By combining an 8-bit RISC CPU
with in-system self-programmable flash on a monolithic chip, the Atmel ATA6612C/ATA6613C uses a powerful
microcontroller that provides a highly flexible and cost effective solution to many embedded control applications.
The Atmel ATA6612C/ATA6613C Atmel AVR is supported with a full suite of program and system development tools
including: C compilers, macro assemblers, program debugger/simulators, in-circuit emulator, and evaluation kits.
5.2.2 Automotive Quality Grade
The Atmel ATA6612C and Atmel ATA6613C have been developed and manufactured according to the most stringent
requirements of the international standard ISO-TS-16949 grade 1. This data sheet contains limit values extracted from the
results of extensive characterization (temperature and voltage). The quality and reliability of the ATA6612C and ATA6613C
have been verified during regular product qualification as per AEC-Q100.
5.2.3 Comparison Between Atmel ATA6612C/ATA6613C
The Atmel ATA6612C and ATA6613C differ only in memory sizes, boot loader support, and interrupt vector sizes.
Table 5-1 summarizes the different memory and interrupt vector sizes for the two devices.
Atmel ATA6612C and ATA6613C support a real read-while-write self-programming mechanism. There is a separate boot
loader section, and the SPM instruction can only execute from there.
5.2.4 Pin Descriptions
5.2.4.1 VCC
Digital supply voltage.
5.2.4.2 GND
Ground.
Table 5-1. Memory Size Summary
Device Flash EEPROM RAM Interrupt Vector Size
ATA6612C 8Kbytes 512Bytes 1Kbyte 1 instruction word/vector
ATA6613C 16Kbytes 512Bytes 1Kbyte 2 instruction words/vector
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5.2.4.3 Port B (PB7:0) XTAL1/XTAL2/TOSC1/TOSC2
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The port B output buffers have
symmetrical drive characteristics with both high sink and source capability. As inputs, Port B pins that are externally pulled
low will source current if the pull-up resistors are activated. The port B pins are tri-stated when a reset condition becomes
active, even if the clock is not running.
Depending on the clock selection fuse settings, PB6 can be used as input to the inverting oscillator amplifier.
Depending on the clock selection fuse settings, PB7 can be used as input to the inverting oscillator amplifier.
If the internal calibrated RC oscillator is used as chip clock source, PB7..6 is used as TOSC2..1 input for the asynchronous
Timer/Counter2 if the AS2 bit in ASSR is set.
The various special features of port B are elaborated in Section 5.10.3.2 “Alternate Functions of Port B” on page 84 and
Section 5.6 “System Clock and Clock Options” on page 46.
5.2.4.4 Port C (PC5:0)
Port C is a 7-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The PC5..0 output buffers have
symmetrical drive characteristics with both high sink and source capability. As inputs, port C pins that are externally pulled
low will source current if the pull-up resistors are activated. The port C pins are tri-stated when a reset condition becomes
active, even if the clock is not running.
5.2.4.5 PC6/RESET
If the RSTDISBL fuse is unprogrammed, PC6 is used as a reset input. A low level on this pin for longer than the minimum
pulse length will generate a reset, even if the clock is not running. The minimum pulse length is given in
Table 5-3 on page 43. Shorter pulses are not guaranteed to generate a reset.
The various special features of port C are elaborated in Section 5.10.3.3 “Alternate Functions of Port C” on page 87.
5.2.4.6 Port D (PD7:0)
Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port D output buffers have
symmetrical drive characteristics with both high sink and source capability. As inputs, Port D pins that are externally pulled
low will source current if the pull-up resistors are activated. The port D pins are tri-stated when a reset condition becomes
active, even if the clock is not running.
The various special features of Port D are elaborated in Section 5.10.3.4 “Alternate Functions of Port D” on page 89.
5.2.4.7 AVCC
AVCC is the supply voltage pin for the A/D converter, PC3:0, and ADC7:6. I should be externally connected to VCC, even if the
ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter. Note that PC6..4 use digital
supply voltage, VCC.
5.2.4.8 AREF
AREF is the analog reference pin for the A/D converter.
5.2.4.9 ADC7:6 (TQFP and QFN Package Only)
In the TQFP and QFN package, ADC7:6 serve as analog inputs to the A/D converter. These pins are powered from the
analog supply and serve as 10-bit ADC channels.
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5.3 About Code Examples
This documentation contains simple code examples that briefly show how to use various parts of the device. These code
examples assume that the part specific header file is included before compilation. Be aware that not all C compiler vendors
include bit definitions in the header file and interrupt handling in C is compiler dependent. Please confirm with the C compiler
documentation for more details.
5.4 AVR CPU Core
5.4.1 Introduction
This section discusses the Atmel AVR® core architecture in general. The main function of the CPU core is to ensure correct
program execution. The CPU must therefore be able to access memories, perform calculations, control peripherals, and
handle interrupts.
5.4.2 Architectural Overview
Figure 5-2. Block Diagram of the Atmel AVR Architecture
Status and
Control
Interrupt
Unit
32 x 8
General
Purpose
Registers
ALU
Data Bus 8 Bit
Data
SRAM
Watchdog
Timer
Instruction
Register
Instruction
Decoder
SPI
Unit
Analog
Comparator
EEPROM
I/O Lines
I/O Module n
Control Lines
Direct Addressing
Indirect Addressing
I/O Module 2
I/O Module 1
Program
Counter
Flash
Program
Memory
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In order to maximize performance and parallelism, the Atmel AVR® uses a harvard architecture – with separate memories
and buses for program and data. Instructions in the program memory are executed with a single level pipelining. While one
instruction is being executed, the next instruction is pre-fetched from the program memory. This concept enables instructions
to be executed in every clock cycle. The program memory is in-system reprogrammable flash memory.
The fast-access register file contains 32 × 8-bit general purpose working registers with a single clock cycle access time. This
allows single-cycle arithmetic logic unit (ALU) operation. In a typical ALU operation, two operands are output from the
register file, the operation is executed, and the result is stored back in the register file – in one clock cycle.
Six of the 32 registers can be used as three 16-bit indirect address register pointers for data space addressing – enabling
efficient address calculations. One of the these address pointers can also be used as an address pointer for look up tables in
flash program memory. These added function registers are the 16-bit X-, Y-, and Z-register, described later in this section.
The ALU supports arithmetic and logic operations between registers or between a constant and a register. Single register
operations can also be executed in the ALU. After an arithmetic operation, the status register is updated to reflect
information about the result of the operation.
Program flow is provided by conditional and unconditional jump and call instructions, able to directly address the whole
address space. Most AVR instructions have a single 16-bit word format. Every program memory address contains a 16- or
32-bit instruction.
Program flash memory space is divided in two sections, the boot program section and the application program section. Both
sections have dedicated lock bits for write and read/write protection. The SPM instruction that writes into the application flash
memory section must reside in the boot program section.
During interrupts and subroutine calls, the return address program counter (PC) is stored on the stack. The stack is
effectively allocated in the general data SRAM, and consequently the stack size is only limited by the total SRAM size and
the usage of the SRAM. All user programs must initialize the SP in the reset routine (before subroutines or interrupts are
executed). The stack pointer (SP) is read/write accessible in the I/O space. The data SRAM can easily be accessed through
the five different addressing modes supported in the AVR architecture.
The memory spaces in the AVR architecture are all linear and regular memory maps.
A flexible interrupt module has its control registers in the I/O space with an additional global interrupt enable bit in the status
register. All interrupts have a separate interrupt vector in the interrupt vector table. The interrupts have priority in accordance
with their interrupt vector position. The lower the interrupt vector address, the higher the priority.
The I/O memory space contains 64 addresses for CPU peripheral functions as control registers, SPI, and other I/O functions.
The I/O memory can be accessed directly, or as the data space locations following those of the register file, 0x20 - 0x5F. In
addition, the Atmel® ATA6612C/ATA6613C has extended I/O space from 0x60 - 0xFF in SRAM where only the ST/STS/STD
and LD/LDS/LDD instructions can be used.
5.4.3 ALU – Arithmetic Logic Unit
The high-performance AVR ALU operates in direct connection with all the 32 general purpose working registers. Within a
single clock cycle, arithmetic operations between general purpose registers or between a register and an immediate are
executed. The ALU operations are divided into three main categories – arithmetic, logical, and bit-functions. Some
implementations of the architecture also provide a powerful multiplier supporting both signed/unsigned multiplication and
fractional format. See the “instruction set” section for a detailed description.
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5.4.4 Status Register
The status register contains information about the result of the most recently executed arithmetic instruction. This
information can be used for altering program flow in order to perform conditional operations. Note that the status register is
updated after all ALU operations, as specified in the instruction set reference. This will in many cases remove the need for
using the dedicated compare instructions, resulting in faster and more compact code.
The status register is not automatically stored when entering an interrupt routine and restored when returning from an
interrupt. This must be handled by software.
The AVR® status register – SREG – is defined as:
• Bit 7 – I: Global Interrupt Enable
The global interrupt enable bit must be set for the interrupts to be enabled. The individual interrupt enable control is then
performed in separate control registers. If the global interrupt enable register is cleared, none of the interrupts are enabled
independent of the individual interrupt enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is
set by the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared by the application with the
SEI and CLI instructions, as described in the instruction set reference.
• Bit 6 – T: Bit Copy Storage
The bit copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or destination for the operated bit. A bit
from a register in the register file can be copied into T by the BST instruction, and a bit in T can be copied into a bit in a
register in the register file by the BLD instruction.
• Bit 5 – H: Half Carry Flag
The half carry flag H indicates a half carry in some arithmetic operations. Half carry is useful in BCD arithmetic. See the
“Instruction Set Description” for detailed information.
• Bit 4 – S: Sign Bit, S = N ⊕ V
The S-bit is always an exclusive or between the negative flag N and the two’s complement overflow flag V. See the
“Instruction Set Description” for detailed information.
• Bit 3 – V: Two’s Complement Overflow Flag
The two’s complement overflow flag V supports two’s complement arithmetics. See the “Instruction Set Description” for
detailed information.
• Bit 2 – N: Negative Flag
The negative flag N indicates a negative result in an arithmetic or logic operation. See the “Instruction Set Description” for
detailed information.
• Bit 1 – Z: Zero Flag
The zero flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction Set Description” for detailed
information.
• Bit 0 – C: Carry Flag
The carry flag C indicates a carry in an arithmetic or logic operation. See the “Instruction Set Description” for detailed
information.
Bit 76543210
ITHSVNZCSREG
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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5.4.5 General Purpose Register File
The register file is optimized for the AVR® enhanced RISC instruction set. In order to achieve the required performance and
flexibility, the following input/output schemes are supported by the register file:
●One 8-bit output operand and one 8-bit result input
●Two 8-bit output operands and one 8-bit result input
●Two 8-bit output operands and one 16-bit result input
●One 16-bit output operand and one 16-bit result input
Figure 5-3 shows the structure of the 32 general purpose working registers in the CPU.
Figure 5-3. AVR CPU General Purpose Working Registers
Most of the instructions operating on the register file have direct access to all registers, and most of them are single cycle
instructions.
As shown in Figure 5-3, each register is also assigned a data memory address, mapping them directly into the first
32 locations of the user data space. Although not being physically implemented as SRAM locations, this memory
organization provides great flexibility in access of the registers, as the X-, Y- and Z-pointer registers can be set to index any
register in the file.
General
Purpose
Working
Registers
7 0 Address
R0 0x00
R1 0x01
R2 0x02
...
R13 0x0D
R14 0x0E
R15 0x0F
R16 0x10
R17 0x11
...
R26 0x1A X-register Low Byte
R27 0x1B X-register High Byte
R28 0x1C Y-register Low Byte
R29 0x1D Y-register High Byte
R30 0x1E Z-register Low Byte
R31 0x1F Z-register High Byte
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5.4.5.1 The X-register, Y-register, and Z-register
The registers R26..R31 have some added functions to their general purpose usage. These registers are 16-bit address
pointers for indirect addressing of the data space. The three indirect address registers X, Y, and Z are defined as described
in Figure 5-4.
Figure 5-4. The X-, Y-, and Z-registers
In the different addressing modes these address registers have functions as fixed displacement, automatic increment, and
automatic decrement (see the instruction set reference for details).
5.4.6 Stack Pointer
The stack is mainly used for storing temporary data, for storing local variables and for storing return addresses after
interrupts and subroutine calls. The stack pointer register always points to the top of the stack. Note that the stack is
implemented as growing from higher memory locations to lower memory locations. This implies that a stack PUSH command
decreases the stack pointer.
The stack pointer points to the data SRAM Stack area where the subroutine and interrupt stacks are located. This stack
space in the data SRAM must be defined by the program before any subroutine calls are executed or interrupts are enabled.
The stack pointer must be set to point above 0x0100, preferably RAMEND. The stack pointer is decremented by one when
data is pushed onto the stack with the PUSH instruction, and it is decremented by two when the return address is pushed
onto the stack with subroutine call or interrupt. The stack pointer is incremented by one when data is popped from the stack
with the POP instruction, and it is incremented by two when data is popped from the stack with return from subroutine RET
or return from interrupt RETI.
The AVR® stack pointer is implemented as two 8-bit registers in the I/O space. The number of bits actually used is
implementation dependent. Note that the data space in some implementations of the AVR architecture is so small that only
SPL is needed. In this case, the SPH register will not be present.
15 XH XL 0
X-register 7 0 7 0
R27 (0x1B) R26 (0x1A)
15 YH YL 0
Y-register 7 0 7 0
R29 (0x1D) R28 (0x1C)
15 ZH ZL 0
Z-register 7 0 7 0
R31 (0x1F) R30 (0x1E)
Bit 151413121110 9 8
SP15 SP14 SP13 SP12 SP11 SP10 SP9 SP8 SPH
SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SPL
76543210
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND
RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND
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5.4.7 Instruction Execution Timing
This section describes the general access timing concepts for instruction execution. The AVR® CPU is driven by the CPU
clock clkCPU, directly generated from the selected clock source for the chip. No internal clock division is used.
Figure 5-5 shows the parallel instruction fetches and instruction executions enabled by the harvard architecture and the
fast-access register file concept. This is the basic pipelining concept to obtain up to 1MIPS per MHz with the corresponding
unique results for functions per cost, functions per clocks, and functions per power-unit.
Figure 5-5. The Parallel Instruction Fetches and Instruction Executions
Figure 5-6 shows the internal timing concept for the register file. In a single clock cycle an ALU operation using two register
operands is executed, and the result is stored back to the destination register.
Figure 5-6. Single Cycle ALU Operation
5.4.8 Reset and Interrupt Handling
The AVR provides several different interrupt sources. These interrupts and the separate reset vector each have a separate
program vector in the program memory space. All interrupts are assigned individual enable bits which must be written logic
one together with the global interrupt enable bit in the status register in order to enable the interrupt. Depending on the
program counter value, interrupts may be automatically disabled when boot lock bits BLB02 or BLB12 are programmed. This
feature improves software security. See Section 5.24 “Memory Programming” on page 253 for details.
The lowest addresses in the program memory space are by default defined as the reset and Interrupt vectors. The complete
list of vectors is shown in Section 5.9 “Interrupts” on page 70. The list also determines the priority levels of the different
interrupts. The lower the address the higher is the priority level. RESET has the highest priority, and next is INT0 – the
external interrupt request 0. The interrupt vectors can be moved to the start of the boot flash section by setting the IVSEL bit
in the MCU control register (MCUCR). Refer to Section 5.9 “Interrupts” on page 70 for more information. The reset vector
can also be moved to the start of the boot flash section by programming the BOOTRST fuse (see Section 5.23 “Boot Loader
Support – Read-While-Write Self-Programming, Atmel ATA6612C and ATA6613C” on page 240).
When an interrupt occurs, the global interrupt enable I-bit is cleared and all interrupts are disabled. The user software can
write logic one to the I-bit to enable nested interrupts. All enabled interrupts can then interrupt the current interrupt routine.
The I-bit is automatically set when a return from interrupt instruction – RETI – is executed.
clkCPU
1st Instruction Fetch
1st Instruction Execute
2nd Instruction Fetch
T1 T2 T3 T4
2nd Instruction Execute
3rd Instruction Fetch
3rd Instruction Execute
4th Instruction Fetch
clkCPU
T1
Register Operands Fetch
Result Write Back
ALU Operation Execute
Total Execution Time
T2 T3 T4
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There are basically two types of interrupts. The first type is triggered by an event that sets the interrupt flag. For these
interrupts, the program counter is vectored to the actual interrupt vector in order to execute the interrupt handling routine,
and hardware clears the corresponding interrupt flag. Interrupt flags can also be cleared by writing a logic one to the flag bit
position(s) to be cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is cleared, the interrupt
flag will be set and remembered until the interrupt is enabled, or the flag is cleared by software. Similarly, if one or more
interrupt conditions occur while the global interrupt enable bit is cleared, the corresponding interrupt flag(s) will be set and
remembered until the global interrupt enable bit is set, and will then be executed by order of priority.
The second type of interrupts will trigger as long as the interrupt condition is present. These interrupts do not necessarily
have interrupt flags. If the interrupt condition disappears before the interrupt is enabled, the interrupt will not be triggered.
When the AVR® exits from an interrupt, it will always return to the main program and execute one more instruction before
any pending interrupt is served.
Note that the status register is not automatically stored when entering an interrupt routine, nor restored when returning from
an interrupt routine. This must be handled by software.
When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled. No interrupt will be executed
after the CLI instruction, even if it occurs simultaneously with the CLI instruction. The following example shows how this can
be used to avoid interrupts during the timed EEPROM write sequence.
When using the SEI instruction to enable interrupts, the instruction following SEI will be executed before any pending
interrupts, as shown in this example.
5.4.8.1 Interrupt Response Time
The interrupt execution response for all the enabled AVR interrupts is four clock cycles minimum. After four clock cycles the
program vector address for the actual interrupt handling routine is executed. During this four clock cycle period, the program
counter is pushed onto the stack. The vector is normally a jump to the interrupt routine, and this jump takes three clock
cycles. If an interrupt occurs during execution of a multi-cycle instruction, this instruction is completed before the interrupt is
served. If an interrupt occurs when the MCU is in sleep mode, the interrupt execution response time is increased by four
clock cycles. This increase comes in addition to the start-up time from the selected sleep mode.
A return from an interrupt handling routine takes four clock cycles. During these four clock cycles, the program counter (two
bytes) is popped back from the stack, the stack pointer is incremented by two, and the I-bit in SREG is set.
Assembly Code Example
in r16, SREG ; store SREG value
cli ; disable interrupts during timed sequence
sbi EECR, EEMPE ; start EEPROM write
sbi EECR, EEPE
out SREG, r16 ; restore SREG value (I-bit)
C Code Example
char cSREG;
cSREG = SREG; /* store SREG value */
/* disable interrupts during timed sequence */
_CLI();
EECR |= (1<<EEMPE); /* start EEPROM write */
EECR |= (1<<EEPE);
SREG = cSREG; /* restore SREG value (I-bit) */
Assembly Code Example
sei ; set Global Interrupt Enable
sleep ; enter sleep, waiting for interrupt
; note: will enter sleep before any pending interrupt(s)
C Code Example
__enable_interrupt(); /* set Global Interrupt Enable */
__sleep(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */
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5.5 AVR Atmel ATA6612C/ATA6613C Memories
This section describes the different memories in the Atmel® ATA6612C/ATA6613C. The AVR® architecture has two main
memory spaces, the data memory and the program memory space. In addition, the Atmel ATA6612C/ATA6613C features
an EEPROM memory for data storage. All three memory spaces are linear and regular.
5.5.1 In-System Reprogrammable Flash Program Memory
The Atmel ATA6612C/ATA6613C contains 8/16Kbytes on-chip in-system reprogrammable flash memory for program
storage. Since all AVR instructions are 16 or 32 bits wide, the flash is organized as 2/4/8K × 16. For software security, the
flash program memory space is divided into two sections, boot loader section and application program section in Atmel
ATA6612C and ATA6613C. See SELFPRGEN description in section Section 5.23.5.1 “Store Program Memory Control and
Status Register – SPMCSR” on page 244 for more details.
The flash memory has an endurance of at least 75,000 write/erase cycles. The Atmel ATA6612C/ATA6613C program
counter (PC) is 11/12/13 bits wide, thus addressing the 2/4/8K program memory locations. The operation of boot program
section and associated boot lock bits for software protection are described in detail in Section 5.23 “Boot Loader Support –
Read-While-Write Self-Programming, Atmel ATA6612C and ATA6613C” on page 240. Section 5.24 “Memory Programming”
on page 253 contains a detailed description on flash programming in SPI- or parallel programming mode.
Constant tables can be allocated within the entire program memory address space (see the LPM – load program memory
instruction description).
Timing diagrams for instruction fetch and execution are presented in Section 5.4.7 “Instruction Execution Timing” on page
36.
Figure 5-7. Program Memory Map, Atmel ATA6612C/ATA6613C
0x0000
0x7FF
Program Memory
Application Flash Section
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Figure 5-8. Program Memory Map, Atmel ATA6612C/ATA6613C
5.5.2 SRAM Data Memory
Figure 5-9 shows how the Atmel® ATA6612C/ATA6613C SRAM memory is organized.
The Atmel ATA6612C/ATA6613C is a complex microcontroller with more peripheral units than can be supported within the
64 locations reserved in the opcode for the IN and OUT instructions. For the extended I/O space from 0x60 - 0xFF in SRAM,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
The lower 768/1280/1280 data memory locations address both the register file, the I/O memory, extended I/O memory, and
the internal data SRAM. The first 32 locations address the register file, the next 64 location the standard I/O memory, then
160 locations of extended I/O memory, and the next 512/1024/1024 locations address the internal data SRAM.
The five different addressing modes for the data memory cover: Direct, indirect with displacement, indirect, indirect with
pre-decrement, and indirect with post-increment. In the register file, registers R26 to R31 feature the indirect addressing
pointer registers.
The direct addressing reaches the entire data space.
The indirect with displacement mode reaches 63 address locations from the base address given by the Y- or Z-register.
When using register indirect addressing modes with automatic pre-decrement and post-increment, the address registers X,
Y, and Z are decremented or incremented.
The 32 general purpose working registers, 64 I/O registers, 160 extended I/O registers, and the 512/1024/1024 bytes of
internal data SRAM in the Atmel ATA6612C/ATA6613C are all accessible through all these addressing modes. The register
file is described in Section 5.4.5 “General Purpose Register File” on page 34.
Figure 5-9. Data Memory Map
0x0000
0x0FFF/0x1FFF
Boot Flash Section
Program Memory
Application Flash Section
32 Registers
64 I/O Registers
Data Memory
0x0000 - 0x001F
0x0020 - 0x005F
0x0060 - 0x00FF
0x0100
0x02FF/0x04FF/0x04FF
160 Ext I/O Registers
Internal SRAM
(512/1024/1024 x 8)
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5.5.2.1 Data Memory Access Times
This section describes the general access timing concepts for internal memory access. The internal data SRAM access is
performed in two clkCPU cycles as described in Figure 5-10.
Figure 5-10. On-chip Data SRAM Access Cycles
5.5.3 EEPROM Data Memory
The Atmel® ATA6612C/ATA6613C contains 512 bytes of data EEPROM memory. It is organized as a separate data space,
in which single bytes can be read and written. The EEPROM has an endurance of at least 100,000 write/erase cycles. The
access between the EEPROM and the CPU is described in the following, specifying the EEPROM address registers, the
EEPROM data register, and the EEPROM control register.
The section Section 5.24 “Memory Programming” on page 253 contains a detailed description on EEPROM programming in
SPI or parallel programming mode.
5.5.3.1 EEPROM Read/Write Access
The EEPROM access registers are accessible in the I/O space.
The write access time for the EEPROM is given in Table 5-3 on page 43. A self-timing function, however, lets the user
software detect when the next byte can be written. If the user code contains instructions that write the EEPROM, some
precautions must be taken. In heavily filtered power supplies, VCC is likely to rise or fall slowly on power-up/down. This
causes the device for some period of time to run at a voltage lower than specified as minimum for the clock frequency used.
See Section 5.5.3.5 “Preventing EEPROM Corruption” on page 44 for details on how to avoid problems in these situations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed. Refer to the description of the
EEPROM control register for details on this.
When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is executed. When the
EEPROM is written, the CPU is halted for two clock cycles before the next instruction is executed.
clkCPU
T1
Data
Data
RD
WR
Address validCompute Address
Next Instruction
Write
Read
Memory Access Instruction
A
ddress
T2 T3
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5.5.3.2 The EEPROM Address Register – EEARH and EEARL
• Bits 15..9 – Res: Reserved Bits
These bits are reserved bits in the Atmel® ATA6612C/ATA6613C and will always read as zero.
• Bits 8..0 – EEAR8..0: EEPROM Address
The EEPROM address registers – EEARH and EEARL specify the EEPROM address in the 512 bytes EEPROM space. The
EEPROM data bytes are addressed linearly between 0 and 255/511/511. The initial value of EEAR is undefined. A proper
value must be written before the EEPROM may be accessed.
5.5.3.3 The EEPROM Data Register – EEDR
• Bits 7..0 – EEDR7.0: EEPROM Data
For the EEPROM write operation, the EEDR register contains the data to be written to the EEPROM in the address given by
the EEAR register. For the EEPROM read operation, the EEDR contains the data read out from the EEPROM at the address
given by EEAR.
5.5.3.4 The EEPROM Control Register – EECR
• Bits 7..6 – Res: Reserved Bits
These bits are reserved bits in the Atmel ATA6612C/ATA6613C and will always read as zero
• Bits 5, 4 – EEPM1 and EEPM0: EEPROM Programming Mode Bits
The EEPROM programming mode bit setting defines which programming action that will be triggered when writing EEPE. It
is possible to program data in one atomic operation (erase the old value and program the new value) or to split the erase and
write operations in two different operations.
The programming times for the different modes are shown in Table 5-2 on page 42. While EEPE is set, any write to EEPMn
will be ignored. During reset, the EEPMn bits will be reset to 0b00 unless the EEPROM is busy programming.
Bit 151413121110 9 8
–––––––EEAR8EEARH
EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEARL
76543210
Read/Write RRRRRRRR/W
R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value0000000X
XXXXXXXX
Bit 76543210
MSB LSB EEDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
– – EEPM1 EEPM0 EERIE EEMPE EEPE EERE EECR
Read/Write R R R/W R/W R/W R/W R/W R/W
Initial Value 0 0 X X 0 0 X 0
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• Bit 3 – EERIE: EEPROM Ready Interrupt Enable
Writing EERIE to one enables the EEPROM ready interrupt if the I bit in SREG is set. Writing EERIE to zero disables the
interrupt. The EEPROM ready interrupt generates a constant interrupt when EEPE is cleared.
• Bit 2 – EEMPE: EEPROM Master Write Enable
The EEMPE bit determines whether setting EEPE to one causes the EEPROM to be written. When EEMPE is set,
setting EEPE within four clock cycles will write data to the EEPROM at the selected address If EEMPE is zero, setting
EEPE will have no effect. When EEMPE has been written to one by software, hardware clears the bit to zero after four
clock cycles. See the description of the EEPE bit for an EEPROM write procedure.
• Bit 1 – EEPE: EEPROM Write Enable
The EEPROM write enable signal EEPE is the write strobe to the EEPROM. When address and data are correctly set
up, the EEPE bit must be written to one to write the value into the EEPROM. The EEMPE bit must be written to one
before a logical one is written to EEPE, otherwise no EEPROM write takes place. The following procedure should be
followed when writing the EEPROM (the order of steps 3 and 4 is not essential):
1. Wait until EEPE becomes zero.
2. Wait until SELFPRGEN in SPMCSR becomes zero.
3. Write new EEPROM address to EEAR (optional).
4. Write new EEPROM data to EEDR (optional).
5. Write a logical one to the EEMPE bit while writing a zero to EEPE in EECR.
6. Within four clock cycles after setting EEMPE, write a logical one to EEPE.
The EEPROM can not be programmed during a CPU write to the flash memory. The software must check that the flash
programming is completed before initiating a new EEPROM write. Step 2 is only relevant if the software contains a boot
loader allowing the CPU to program the flash. If the flash is never being updated by the CPU, step 2 can be omitted. See
Section 5.23 “Boot Loader Support – Read-While-Write Self-Programming, Atmel ATA6612C and ATA6613C” on page 240
for details about boot programming.
Caution: An interrupt between step 5 and step 6 will make the write cycle fail, since the EEPROM master write enable
will time-out. If an interrupt routine accessing the EEPROM is interrupting another EEPROM access, the EEAR
or EEDR register will be modified, causing the interrupted EEPROM access to fail. It is recommended to have
the global interrupt flag cleared during all the steps to avoid these problems.
When the write access time has elapsed, the EEPE bit is cleared by hardware. The user software can poll this bit and wait
for a zero before writing the next byte. When EEPE has been set, the CPU is halted for two cycles before the next instruction
is executed.
• Bit 0 – EERE: EEPROM Read Enable
The EEPROM read enable signal EERE is the read strobe to the EEPROM. When the correct address is set up in the EEAR
register, the EERE bit must be written to a logic one to trigger the EEPROM read. The EEPROM read access takes one
instruction, and the requested data is available immediately. When the EEPROM is read, the CPU is halted for four cycles
before the next instruction is executed.
Table 5-2. EEPROM Mode Bits
EEPM1 EEPM0 Programming Time Operation
0 0 3.4ms Erase and write in one operation (atomic operation)
0 1 1.8ms Erase only
1 0 1.8ms Write only
1 1 – Reserved for future use
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The user should poll the EEPE bit before starting the read operation. If a write operation is in progress, it is neither possible
to read the EEPROM, nor to change the EEAR register.
The calibrated oscillator is used to time the EEPROM accesses. Table 5-3 lists the typical programming time for EEPROM
access from the CPU.
The following code examples show one assembly and one C function for writing to the EEPROM. The examples assume
that interrupts are controlled (e.g. by disabling interrupts globally) so that no interrupts will occur during execution of these
functions. The examples also assume that no flash boot loader is present in the software. If such code is present, the
EEPROM write function must also wait for any ongoing SPM command to finish.
Table 5-3. EEPROM Programming Time
Symbol Number of Calibrated RC Oscillator Cycles Typ Programming Time
EEPROM write (from CPU) 26,368 3.3ms
Assembly Code Example
EEPROM_write:
; Wait for completion of previous write
sbic EECR,EEPE
rjmp EEPROM_write
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Write data (r16) to Data Register
out EEDR,r16
; Write logical one to EEMPE
sbi EECR,EEMPE
; Start eeprom write by setting EEPE
sbi EECR,EEPE
ret
C Code Example
void EEPROM_write(unsigned int uiAddress, unsigned char ucData)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set up address and Data Registers */
EEAR = uiAddress;
EEDR = ucData;
/* Write logical one to EEMPE */
EECR |= (1<<EEMPE);
/* Start eeprom write by setting EEPE */
EECR |= (1<<EEPE);
}
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The next code examples show assembly and C functions for reading the EEPROM. The examples assume that interrupts
are controlled so that no interrupts will occur during execution of these functions.
5.5.3.5 Preventing EEPROM Corruption
During periods of low VCC, the EEPROM data can be corrupted because the supply voltage is too low for the CPU and the
EEPROM to operate properly. These issues are the same as for board level systems using EEPROM, and the same design
solutions should be applied.
An EEPROM data corruption can be caused by two situations when the voltage is too low. First, a regular write sequence to
the EEPROM requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute instructions incorrectly,
if the supply voltage is too low.
EEPROM data corruption can easily be avoided by following this design recommendation:
Keep the AVR® RESET active (low) during periods of insufficient power supply voltage. This can be done by enabling the
internal brown-out detector (BOD). If the detection level of the internal BOD does not match the needed detection level, an
external low VCC reset protection circuit can be used. If a reset occurs while a write operation is in progress, the write
operation will be completed provided that the power supply voltage is sufficient.
Assembly Code Example
EEPROM_read:
; Wait for completion of previous write
sbic EECR,EEPE
rjmp EEPROM_read
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Start eeprom read by writing EERE
sbi EECR,EERE
; Read data from Data Register
in r16,EEDR
ret
C Code Example
unsigned char EEPROM_read(unsigned int uiAddress)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set up address register */
EEAR = uiAddress;
/* Start eeprom read by writing EERE */
EECR |= (1<<EERE);
/* Return data from Data Register */
return EEDR;
}
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5.5.4 I/O Memory
The I/O space definition of the Atmel® ATA6612C/ATA6613C is shown in Section 6.4 “Register Summary” on page 291.
All Atmel ATA6612C/ATA6613C I/Os and peripherals are placed in the I/O space. All I/O locations may be accessed by the
LD/LDS/LDD and ST/STS/STD instructions, transferring data between the 32 general purpose working registers and the I/O
space. I/O registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In
these registers, the value of single bits can be checked by using the SBIS and SBIC instructions. Refer to the instruction set
section for more details. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used.
When addressing I/O registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The
Atmel ATA6612C/ATA6613C is a complex microcontroller with more peripheral units than can be supported within the 64
location reserved in opcode for the IN and OUT instructions. For the extended I/O space from 0x60 - 0xFF in SRAM, only the
ST/STS/STD and LD/LDS/LDD instructions can be used.
For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses
should never be written. Some of the status flags are cleared by writing a logical one to them. Note that, unlike most other
AVR®s, the CBI and SBI instructions will only operate on the specified bit, and can therefore be used on registers containing
such status flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only. The I/O and peripherals control
registers are explained in later sections.
5.5.4.1 General Purpose I/O Registers
The Atmel ATA6612C/ATA6613C contains three general purpose I/O registers. These registers can be used for storing any
information, and they are particularly useful for storing global variables and status flags. General purpose I/O registers within
the address range 0x00 - 0x1F are directly bit-accessible using the SBI, CBI, SBIS, and SBIC instructions.
5.5.4.2 General Purpose I/O Register 2 – GPIOR2
5.5.4.3 General Purpose I/O Register 1 – GPIOR1
5.5.4.4 General Purpose I/O Register 0 – GPIOR0
Bit 76543210
MSB LSB GPIOR2
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
MSB LSB GPIOR1
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
MSB LSB GPIOR0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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5.6 System Clock and Clock Options
5.6.1 Clock Systems and their Distribution
Figure 5-11 presents the principal clock systems in the AVR® and their distribution. All of the clocks need not be active at a
given time. In order to reduce power consumption, the clocks to modules not being used can be halted by using different
sleep modes, as described in Section 5.7 “Power Management and Sleep Modes” on page 55. The clock systems are
detailed below.
Figure 5-11. Clock Distribution
5.6.1.1 CPU Clock – clkCPU
The CPU clock is routed to parts of the system concerned with operation of the AVR core. Examples of such modules are
the general purpose register file, the status register and the data memory holding the stack pointer. Halting the CPU clock
inhibits the core from performing general operations and calculations.
5.6.1.2 I/O Clock – clkI/O
The I/O clock is used by the majority of the I/O modules, like Timer/Counters, SPI, and USART. The I/O clock is also used by
the external interrupt module, but note that some external interrupts are detected by asynchronous logic, allowing such
interrupts to be detected even if the I/O clock is halted. Also note that start condition detection in the USI module is carried
out asynchronously when clkI/O is halted, TWI address recognition in all sleep modes.
5.6.1.3 Flash Clock – clkFLASH
The flash clock controls operation of the flash interface. The flash clock is usually active simultaneously with the CPU clock.
5.6.1.4 Asynchronous Timer Clock – clkASY
The asynchronous timer clock allows the asynchronous Timer/Counter to be clocked directly from an external clock or an
external 32kHz clock crystal. The dedicated clock domain allows using this Timer/Counter as a real-time counter even when
the device is in sleep mode.
Asynchronous
Timer/Counter
Flash and
EEPROM
Timer/Counter
Oscillator
Calibrated RC
Oscillator
Low Frequency
Crystal Oscillator
Crystal
Oscillator
Watchdog
Oscillator
System Clock
Prescaler
General I/O
Modules
AVR Clock
Control Unit
ADC
External Clock
CPU Core
Source clock Watchdog clock
RAM
Reset Logic Watchdog Timer
clkI/O
clkASY
clkCPU
clkADC
clkFLASH
Clock
Multiplexer
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5.6.1.5 ADC Clock – clkADC
The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O clocks in order to reduce noise
generated by digital circuitry. This gives more accurate ADC conversion results.
5.6.2 Clock Sources
The device has the following clock source options, selectable by flash fuse bits as shown below. The clock from the selected
source is input to the AVR® clock generator, and routed to the appropriate modules.
5.6.2.1 Default Clock Source
The device is shipped with internal RC oscillator at 8.0MHz and with the fuse CKDIV8 programmed, resulting in 1.0MHz
system clock. The startup time is set to maximum and time-out period enabled. (CKSEL = “0010”, SUT = “10”,
CKDIV8 = “0”). The default setting ensures that all users can make their desired clock source setting using any available
programming interface.
5.6.2.2 Clock Startup Sequence
Any clock source needs a sufficient VCC to start oscillating and a minimum number of oscillating cycles before it can be
considered stable.
To ensure sufficient VCC, the device issues an internal reset with a time-out delay (tTOUT) after the device reset is released by
all other reset sources. The Section 5.8 “System Control and Reset” on page 60 describes the start conditions for the internal
reset. The delay (tTOUT) is timed from the watchdog oscillator and the number of cycles in the delay is set by the SUTx and
CKSELx fuse bits. The selectable delays are shown in Table 5-5. The frequency of the watchdog oscillator is voltage
dependent as shown in Section 6.4 “Register Summary” on page 291.
Main purpose of the delay is to keep the AVR in reset until it is supplied with minimum VCC. The delay will not monitor the
actual voltage and it will be required to select a delay longer than the VCC rise time. If this is not possible, an internal or
external brown-out detection circuit should be used. A BOD circuit will ensure sufficient VCC before it releases the reset, and
the time-out delay can be disabled. Disabling the time-out delay without utilizing a brown-out detection circuit is not
recommended.
Table 5-4. Device Clocking Options Select(1)
Device Clocking Option CKSEL3..0
Low power crystal oscillator 1111 - 1000
Full swing crystal oscillator 0111 - 0110
Low frequency crystal oscillator 0101 - 0100
Internal 128kHz RC oscillator 0011
Calibrated internal RC oscillator 0010
External clock 0000
Reserved 0001
Note: 1. For all fuses “1” means unprogrammed while “0” means programmed.
Table 5-5. Number of Watchdog Oscillator Cycles
Typ Time-out (VCC = 5.0V) Typ Time-out (VCC = 3.0V) Number of Cycles
0ms 0ms 0
4.1ms 4.3ms 4K (4,096)
65ms 69ms 8K (8,192)
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The oscillator is required to oscillate for a minimum number of cycles before the clock is considered stable. An internal ripple
counter monitors the oscillator output clock, and keeps the internal reset active for a given number of clock cycles. The reset
is then released and the device will start to execute. The recommended oscillator start-up time is dependent on the clock
type, and varies from 6 cycles for an externally applied clock to 32K cycles for a low frequency crystal.
The start-up sequence for the clock includes both the time-out delay and the start-up time when the device starts up from
reset. When starting up from power-save or power-down mode, VCC is assumed to be at a sufficient level and only the
start-up time is included.
5.6.3 Low Power Crystal Oscillator
Pins XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be configured for use as an
on-chip oscillator, as shown in Figure 5-12. Either a quartz crystal or a ceramic resonator may be used.
This crystal oscillator is a low power oscillator, with reduced voltage swing on the XTAL2 output. It gives the lowest power
consumption, but is not capable of driving other clock inputs, and may be more susceptible to noise in noisy environments. In
these cases, refer to the Section 5.6.4 “Full Swing Crystal Oscillator” on page 49.
C1 and C2 should always be equal for both crystals and resonators. The optimal value of the capacitors depends on the
crystal or resonator in use, the amount of stray capacitance, and the electromagnetic noise of the environment. Some initial
guidelines for choosing capacitors for use with crystals are given in Table 5-6. For ceramic resonators, the capacitor values
given by the manufacturer should be used.
Figure 5-12. Crystal Oscillator Connections
The low power oscillator can operate in three different modes, each optimized for a specific frequency range. The operating
mode is selected by the fuses CKSEL3..1 as shown in Table 5-6.
Table 5-6. Low Power Crystal Oscillator Operating Modes(3)
Frequency Range(1) (MHz) CKSEL3..1 Recommended Range for Capacitors C1 and C2 (pF)
0.4 - 0.9 100(2) –
0.9 - 3.0 101 12 - 22
3.0 - 8.0 110 12 - 22
8.0 - 16.0 111 12 - 22
Notes: 1. The frequency ranges are preliminary values. Actual values are TBD.
2. This option should not be used with crystals, only with ceramic resonators.
3. If 8MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8 Fuse can be pro-
grammed in order to divide the internal frequency by 8. It must be ensured that the resulting divided clock
meets the frequency specification of the device.
C2
XTAL2
XTAL1
GND
C1
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The CKSEL0 fuse together with the SUT1..0 fuses select the start-up times as shown in Table 5-7.
5.6.4 Full Swing Crystal Oscillator
Pins XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be configured for use as an
on-chip oscillator, as shown in Figure 5-12 on page 48. Either a quartz crystal or a ceramic resonator may be used.
This crystal oscillator is a full swing oscillator, with rail-to-rail swing on the XTAL2 output. This is useful for driving other clock
inputs and in noisy environments. The current consumption is higher than the Section 5.6.3 “Low Power Crystal Oscillator”
on page 48. Note that the full swing crystal oscillator will only operate for VCC = 2.7 to 5.5V.
C1 and C2 should always be equal for both crystals and resonators. The optimal value of the capacitors depends on the
crystal or resonator in use, the amount of stray capacitance, and the electromagnetic noise of the environment. Some initial
guidelines for choosing capacitors for use with crystals are given in Table 5-9 on page 50. For ceramic resonators, the
capacitor values given by the manufacturer should be used.
The operating mode is selected by the fuses CKSEL3..1 as shown in Table 5-8.
Table 5-7. Start-up Times for the Low Power Crystal Oscillator Clock Selection
Oscillator Source/ Power
Conditions
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset
(VCC = 5.0V) CKSEL0 SUT1..0
Ceramic resonator, fast rising
power 258CK 14CK + 4.1ms(1) 000
Ceramic resonator, slowly rising
power 258CK 14CK + 65ms(1) 001
Ceramic resonator, BOD
enabled 1KCK 14CK(2) 010
Ceramic resonator, fast rising
power 1KCK 14CK + 4.1ms(2) 011
Ceramic resonator, slowly rising
power 1KCK 14CK + 65ms(2) 100
Crystal oscillator, BOD enabled 16KCK 14CK 101
Crystal oscillator, fast rising
power 16KCK 14CK + 4.1ms 110
Crystal oscillator, slowly rising
power 16KCK 14CK + 65ms 111
Notes: 1. These options should only be used when not operating close to the maximum frequency of the device, and
only if frequency stability at start-up is not important for the application. These options are not suitable for
crystals.
2. These options are intended for use with ceramic resonators and will ensure frequency stability at start-up.
They can also be used with crystals when not operating close to the maximum frequency of the device, and if
frequency stability at start-up is not important for the application.
Table 5-8. Full Swing Crystal Oscillator Operating Modes(2)
Frequency Range(1) (MHz) CKSEL3..1 Recommended Range for Capacitors C1 and C2 (pF)
0.4 - 20 011 12 - 22
Notes: 1. The frequency ranges are preliminary values. Actual values are TBD.
2. If 8MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8 Fuse can be
programmed in order to divide the internal frequency by 8. It must be ensured that the resulting divided clock
meets the frequency specification of the device.
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Figure 5-13. Crystal Oscillator Connections
Table 5-9. Start-up Times for the Full Swing Crystal Oscillator Clock Selection
Oscillator Source/
Power Conditions
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset (VCC = 5.0V) CKSEL0 SUT1..0
Ceramic resonator, fast rising
power 258CK 14CK + 4.1ms(1) 000
Ceramic resonator, slowly rising
power 258CK 14CK + 65ms(1) 001
Ceramic resonator, BOD
enabled 1KCK 14CK(2) 010
Ceramic resonator, fast rising
power 1KCK 14CK + 4.1ms(2) 011
Ceramic resonator, slowly rising
power 1KCK 14CK + 65ms(2) 100
Crystal oscillator, BOD enabled 16KCK 14CK 101
Crystal oscillator, fast rising
power 16KCK 14CK + 4.1ms 110
Crystal oscillator, slowly rising
power 16KCK 14CK + 65ms 111
Notes: 1. These options should only be used when not operating close to the maximum frequency of the device, and
only if frequency stability at start-up is not important for the application. These options are not suitable for
crystals.
2. These options are intended for use with ceramic resonators and will ensure frequency stability at start-up.
They can also be used with crystals when not operating close to the maximum frequency of the device, and if
frequency stability at start-up is not important for the application.
C2
XTAL2
XTAL1
GND
C1
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5.6.5 Low Frequency Crystal Oscillator
The device can utilize a 32.768kHz watch crystal as clock source by a dedicated low frequency crystal oscillator. The crystal
should be connected as shown in Figure 5-12. When this oscillator is selected, start-up times are determined by the SUT
fuses and CKSEL0 as shown in Table 5-10.
5.6.6 Calibrated Internal RC Oscillator
The calibrated internal RC oscillator by default provides a 8.0MHz clock. The frequency is nominal value at 5V and 25°C.
The device is shipped with the CKDIV8 fuse programmed. See Section 5.6.11 “System Clock Prescaler” on page 54 for more
details. This clock may be selected as the system clock by programming the CKSEL fuses as shown in Table 5-11. If
selected, it will operate with no external components. During reset, hardware loads the calibration byte into the OSCCAL
register and thereby automatically calibrates the RC oscillator. At 5V and 25°C, this calibration gives a frequency of 8MHz
±1%. The tolerance of the internal RC oscillator remains better than ±10% within the whole automotive temperature and
voltage ranges (4.5V to 5.5V, –40°C to +125°C). The oscillator can be calibrated to any frequency in the range 7.3 - 8.1MHz
within ±1% accuracy, by changing the OSCCAL register. When this oscillator is used as the chip clock, the watchdog
oscillator will still be used for the watchdog timer and for the reset time-out. For more information on the pre-programmed
calibration value (see Section 5.24.4 “Calibration Byte” on page 256).
Table 5-10. Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
Power Conditions
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset (VCC = 5.0V) CKSEL0 SUT1..0
BOD enabled 1kCK 14CK(1) 000
Fast rising power 1kCK 14CK + 4.1ms(1) 001
Slowly rising power 1kCK 14CK + 65ms(1) 010
Reserved 011
BOD enabled 32kCK 14CK 100
Fast rising power 32kCK 14CK + 4.1ms 101
Slowly rising power 32kCK 14CK + 65ms 110
Reserved 111
Note: 1. These options should only be used if frequency stability at start-up is not important for the application.
Table 5-11. Internal Calibrated RC Oscillator Operating Modes(1)(3)
Frequency Range(2) (MHz) CKSEL3..0
7.3 - 8.1 0010
Notes: 1. The device is shipped with this option selected.
2. The frequency ranges are preliminary values. Actual values are TBD.
3. If 8MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8 fuse can be
programmed in order to divide the internal frequency by 8.
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When this oscillator is selected, start-up times are determined by the SUT fuses as shown in Table 5-12.
5.6.6.1 Oscillator Calibration Register – OSCCAL
• Bits 7..0 – CAL7..0: Oscillator Calibration Value
The oscillator calibration register is used to trim the calibrated internal RC oscillator to remove process variations from the
oscillator frequency. The factory-calibrated value is automatically written to this register during chip reset, giving an oscillator
frequency of 8.0MHz at 25°C. The application software can write this register to change the oscillator frequency. The
oscillator can be calibrated to any frequency in the range 7.3 to 8.1MHz within ±1% accuracy. Calibration outside that range
is not guaranteed.
Note that this oscillator is used to time EEPROM and flash write accesses, and these write times will be affected accordingly.
If the EEPROM or flash are written, do not calibrate to more than 8.8MHz. Otherwise, the EEPROM or flash write may fail.
The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0 gives the lowest frequency range,
setting this bit to 1 gives the highest frequency range. The two frequency ranges are overlapping, in other words a setting of
OSCCAL = 0x7F gives a higher frequency than OSCCAL = 0x80.
The CAL6..0 bits are used to tune the frequency within the selected range. A setting of 0x00 gives the lowest frequency in
that range, and a setting of 0x7F gives the highest frequency in the range. Incrementing CAL6..0 by 1 will give a frequency
increment of less than 2% in the frequency range 7.3 - 8.1MHz.
5.6.7 128kHz Internal Oscillator
The 128kHz internal oscillator is a low power oscillator providing a clock of 128kHz. The frequency is nominal at 3V and
25°C. This clock may be select as the system clock by programming the CKSEL fuses to “11” as shown in Table 5-13.
Table 5-12. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
Power Conditions
Start-up Time from Power-down and
Power-save
Additional Delay from Reset
(VCC = 5.0V) SUT1..0
BOD enabled 6CK 14CK(1) 00
Fast rising power 6CK 14CK + 4.1ms 01
Slowly rising power 6CK 14CK + 65ms(2) 10
Reserved 11
Note: 1. If the RSTDISBL fuse is programmed, this start-up time will be increased to
14CK + 4.1ms to ensure programming mode can be entered.
2. The device is shipped with this option selected.
Bit 76543210
CAL7 CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 OSCCAL
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value Device Specific Calibration Value
Table 5-13. 128kHz Internal Oscillator Operating Modes
Nominal Frequency CKSEL3..0
128kHz 0011
Note: 1. The frequency is preliminary value. Actual value is TBD.
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When this clock source is selected, start-up times are determined by the SUT fuses as shown in Table 5-14.
5.6.8 External Clock
The device can utilize a external clock source as shown in Figure 5-14. To run the device on an external clock, the CKSEL
fuses must be programmed as shown in Table 5-15.
Figure 5-14. External Clock Drive Configuration
When this clock source is selected, start-up times are determined by the SUT fuses as shown in Table 5-16.
Table 5-14. Start-up Times for the 128kHz Internal Oscillator
Power Conditions
Start-up Time from Power-down and
Power-save Additional Delay from Reset SUT1..0
BOD enabled 6CK 14CK(1) 00
Fast rising power 6CK 14CK + 4ms 01
Slowly rising power 6CK 14CK + 64ms 10
Reserved 11
Note: 1. If the RSTDISBL fuse is programmed, this start-up time will be increased to
14CK + 4.1ms to ensure programming mode can be entered.
Table 5-15. Full Swing Crystal Oscillator Operating Modes(2)
Frequency Range(1) (MHz) CKSEL3..0
Recommended Range for Capacitors
C1 and C2 (pF)
0 - 100 0000 12 - 22
Notes: 1. The frequency ranges are preliminary values. Actual values are TBD.
2. If 8MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8 fuse can be
programmed in order to divide the internal frequency by 8. It must be ensured that the resulting divided clock
meets the frequency specification of the device.
Table 5-16. Start-up Times for the External Clock Selection
Power Conditions
Start-up Time from Power-down and
Power-save
Additional Delay from Reset
(VCC = 5.0V) SUT1..0
BOD enabled 6CK 14CK 00
Fast rising power 6CK 14CK + 4.1ms 01
Slowly rising power 6CK 14CK + 65ms 10
Reserved 11
XTAL2
XTAL1
GND
NC
EXTERNAL
CLOCK
SIGNAL
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When applying an external clock, it is required to avoid sudden changes in the applied clock frequency to ensure stable
operation of the MCU. A variation in frequency of more than 2% from one clock cycle to the next can lead to unpredictable
behavior. If changes of more than 2% is required, ensure that the MCU is kept in reset during the changes.
Note that the system clock prescaler can be used to implement run-time changes of the internal clock frequency while still
ensuring stable operation. Refer to Section 5.6.11 “System Clock Prescaler” on page 54 for details.
5.6.9 Clock Output Buffer
The device can output the system clock on the CLKO pin. To enable the output, the CKOUT Fuse has to be programmed.
This mode is suitable when the chip clock is used to drive other circuits on the system. The clock also will be output during
reset, and the normal operation of I/O pin will be overridden when the fuse is programmed. Any clock source, including the
internal RC oscillator, can be selected when the clock is output on CLKO. If the system clock prescaler is used, it is the
divided system clock that is output.
5.6.10 Timer/Counter Oscillator
The device can operate its Timer/Counter2 from an external 32.768kHz watch crystal or a external clock source. The
Timer/Counter oscillator pins (TOSC1 and TOSC2) are shared with XTAL1 and XTAL2. This means that the Timer/Counter
oscillator can only be used when an internal RC oscillator is selected as system clock source. See Figure 5-12 on page 48
for crystal connection.
Applying an external clock source to TOSC1 requires EXTCLK in the ASSR register written to logic one. See Section 5.15.9
“Asynchronous Operation of the Timer/Counter” on page 153 for further description on selecting external clock as input
instead of a 32kHz crystal.
5.6.11 System Clock Prescaler
The Atmel® ATA6612C/ATA6613C has a system clock prescaler, and the system clock can be divided by setting the
Section 5.6.11.1 “Clock Prescale Register – CLKPR” on page 54. This feature can be used to decrease the system clock
frequency and the power consumption when the requirement for processing power is low. This can be used with all clock
source options, and it will affect the clock frequency of the CPU and all synchronous peripherals. clkI/O, clkADC, clkCPU, and
clkFLASH are divided by a factor as shown in Table 5-20 on page 62.
When switching between prescaler settings, the system clock prescaler ensures that no glitches occurs in the clock system.
It also ensures that no intermediate frequency is higher than neither the clock frequency corresponding to the previous
setting, nor the clock frequency corresponding to the new setting. The ripple counter that implements the prescaler runs at
the frequency of the undivided clock, which may be faster than the CPU's clock frequency. Hence, it is not possible to
determine the state of the prescaler - even if it were readable, and the exact time it takes to switch from one clock division to
the other cannot be exactly predicted. From the time the CLKPS values are written, it takes between T1 + T2 and
T1 + 2 ×T2
before the new clock frequency is active. In this interval, 2 active clock edges are produced. Here, T1 is the previous clock
period, and T2 is the period corresponding to the new prescaler setting.
To avoid unintentional changes of clock frequency, a special write procedure must be followed to change the CLKPS bits:
1. Write the clock prescaler change enable (CLKPCE) bit to one and all other bits in CLKPR to zero.
2. Within four cycles, write the desired value to CLKPS while writing a zero to CLKPCE.
Interrupts must be disabled when changing prescaler setting to make sure the write procedure is not interrupted.
5.6.11.1Clock Prescale Register – CLKPR
• Bit 7 – CLKPCE: Clock Prescaler Change Enable
The CLKPCE bit must be written to logic one to enable change of the CLKPS bits. The CLKPCE bit is only updated
when the other bits in CLKPR are simultaneously written to zero. CLKPCE is cleared by hardware four cycles after it
is written or when CLKPS bits are written. Rewriting the CLKPCE bit within this time-out period does neither extend
the time-out period, nor clear the CLKPCE bit.
Bit 76543210
CLKPCE – – – CLKPS3 CLKPS2 CLKPS1 CLKPS0 CLKPR
Read/Write R/W R R R R/W R/W R/W R/W
Initial Value 0 0 0 0 See Bit Description
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• Bits 3..0 – CLKPS3..0: Clock Prescaler Select Bits 3 - 0
These bits define the division factor between the selected clock source and the internal system clock. These bits can
be written run-time to vary the clock frequency to suit the application requirements. As the divider divides the master
clock input to the MCU, the speed of all synchronous peripherals is reduced when a division factor is used.
The division factors are given in Table 5-17.
The CKDIV8 fuse determines the initial value of the CLKPS bits. If CKDIV8 is unprogrammed, the CLKPS bits will be
reset to “0000”. If CKDIV8 is programmed, CLKPS bits are reset to “0011”, giving a division factor of 8 at start up. This
feature should be used if the selected clock source has a higher frequency than the maximum frequency of the device
at the present operating conditions. Note that any value can be written to the CLKPS bits regardless of the CKDIV8
fuse setting. The application software must ensure that a sufficient division factor is chosen if the selected clock
source has a higher frequency than the maximum frequency of the device at the present operating conditions. The
device is shipped with the CKDIV8 fuse programmed.
5.7 Power Management and Sleep Modes
Sleep modes enable the application to shut down unused modules in the MCU, thereby saving power. The AVR® provides
various sleep modes allowing the user to tailor the power consumption to the application’s requirements.
To enter any of the five sleep modes, the SE bit in SMCR must be written to logic one and a SLEEP instruction must be
executed. The SM2, SM1, and SM0 bits in the SMCR register select which sleep mode (idle, ADC noise reduction,
power-down, power-save, or standby) will be activated by the SLEEP instruction. See Table 5-18 on page 56 for a summary.
If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU wakes up. The MCU is then halted for four cycles
in addition to the start-up time, executes the interrupt routine, and resumes execution from the instruction following SLEEP.
The contents of the register file and SRAM are unaltered when the device wakes up from sleep. If a reset occurs during
sleep mode, the MCU wakes up and executes from the reset vector.
Figure 5-11 on page 46 presents the different clock systems in the Atmel® ATA6612C/ATA6613C, and their distribution. The
figure is helpful in selecting an appropriate sleep mode.
Table 5-17. Clock Prescaler Select
CLKPS3 CLKPS2 CLKPS1 CLKPS0 Clock Division Factor
0 0 0 0 1
0 0 0 1 2
0 0 1 0 4
0 0 1 1 8
0 1 0 0 16
0 1 0 1 32
0 1 1 0 64
0 1 1 1 128
1 0 0 0 256
1 0 0 1 Reserved
1 0 1 0 Reserved
1 0 1 1 Reserved
1 1 0 0 Reserved
1 1 0 1 Reserved
1 1 1 0 Reserved
1 1 1 1 Reserved
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5.7.1 Sleep Mode Control Register – SMCR
The sleep mode control register contains control bits for power management.
• Bits 7..4 Res: Reserved Bits
These bits are unused bits in the Atmel® ATA6612C/ATA6613C, and will always read as zero.
• Bits 3..1 – SM2..0: Sleep Mode Select Bits 2, 1, and 0
These bits select between the five available sleep modes as shown in Table 5-18.
• Bit 0 – SE: Sleep Enable
The SE bit must be written to logic one to make the MCU enter the sleep mode when the SLEEP instruction is executed. To
avoid the MCU entering the sleep mode unless it is the programmer’s purpose, it is recommended to write the sleep enable
(SE) bit to one just before the execution of the SLEEP instruction and to clear it immediately after waking up.
5.7.2 Idle Mode
When the SM2..0 bits are written to 000, the SLEEP instruction makes the MCU enter idle mode, stopping the CPU but
allowing the SPI, USART, analog comparator, ADC, 2-wire serial interface, Timer/Counters, watchdog, and the interrupt
system to continue operating. This sleep mode basically halts clkCPU and clkFLASH, while allowing the other clocks to run.
Idle mode enables the MCU to wake up from external triggered interrupts as well as internal ones like the timer overflow and
USART transmit complete interrupts. If wake-up from the analog comparator interrupt is not required, the analog comparator
can be powered down by setting the ACD bit in the analog comparator control and status register – ACSR. This will reduce
power consumption in idle mode. If the ADC is enabled, a conversion starts automatically when this mode is entered.
5.7.3 ADC Noise Reduction Mode
When the SM2..0 bits are written to 001, the SLEEP instruction makes the MCU enter ADC noise reduction mode, stopping
the CPU but allowing the ADC, the external interrupts, the 2-wire serial interface address watch, Timer/Counter2, and the
watchdog to continue operating (if enabled). This sleep mode basically halts clkI/O, clkCPU, and clkFLASH, while allowing the
other clocks to run.
This improves the noise environment for the ADC, enabling higher resolution measurements. If the ADC is enabled, a
conversion starts automatically when this mode is entered. Apart from the ADC conversion complete interrupt, only an
external reset, a watchdog system reset, a watchdog interrupt, a brown-out reset, a 2-wire serial interface address match, a
Timer/Counter2 interrupt, an SPM/EEPROM ready interrupt, an external level interrupt on INT0 or INT1 or a pin change
interrupt can wake up the MCU from ADC noise reduction mode.
Bit 76543210
––––SM2SM1SM0SESMCR
Read/Write RRRRR/WR/WR/WR/W
Initial Value00000000
Table 5-18. Sleep Mode Select
SM2 SM1 SM0 Sleep Mode
000 Idle
001 ADC noise reduction
010 Power-down
011 Power-save
100 Reserved
101 Reserved
110 Standby(1)
111 Reserved
Note: 1. Standby mode is only recommended for use with external crystals or resonators.
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5.7.4 Power-down Mode
When the SM2..0 bits are written to 010, the SLEEP instruction makes the MCU enter power-down mode. In this mode, the
external oscillator is stopped, while the external interrupts, the 2-wire serial interface address watch, and the watchdog
continue operating (if enabled). Only an external reset, a watchdog system reset, a watchdog interrupt, a brown-out reset, a
2-wire serial interface address match, an external level interrupt on INT0 or INT1, or a pin change interrupt can wake up the
MCU. This sleep mode basically halts all generated clocks, allowing operation of asynchronous modules only.
Note that if a level triggered interrupt is used for wake-up from power-down mode, the changed level must be held for some
time to wake up the MCU. Refer to Section 5.11 “External Interrupts” on page 92 for details.
When waking up from power-down mode, there is a delay from the wake-up condition occurs until the wake-up becomes
effective. This allows the clock to restart and become stable after having been stopped. The wake-up period is defined by the
same CKSEL fuses that define the reset time-out period, as described in Section 5.6.2 “Clock Sources” on page 47.
5.7.5 Power-save Mode
When the SM2..0 bits are written to 011, the SLEEP instruction makes the MCU enter power-save mode. This mode is
identical to power-down, with one exception.
If Timer/Counter2 is enabled, it will keep running during sleep. The device can wake up from either timer overflow or output
compare event from Timer/Counter2 if the corresponding Timer/Counter2 interrupt enable bits are set in TIMSK2, and the
global interrupt enable bit in SREG is set.
If Timer/Counter2 is not running, power-down mode is recommended instead of power-save mode.
The Timer/Counter2 can be clocked both synchronously and asynchronously in power-save mode. If Timer/Counter2 is not
using the asynchronous clock, the Timer/Counter oscillator is stopped during sleep. If Timer/Counter2 is not using the
synchronous clock, the clock source is stopped during sleep. Note that even if the synchronous clock is running in
power-save, this clock is only available for Timer/Counter2.
5.7.6 Standby Mode
When the SM2..0 bits are 110 and an external crystal/resonator clock option is selected, the SLEEP instruction makes the
MCU enter standby mode. This mode is identical to power-down with the exception that the oscillator is kept running. From
standby mode, the device wakes up in six clock cycles.
Table 5-19. Active Clock Domains and Wake-up Sources in the Different Sleep Modes
Sleep Mode
Active Clock Domains Oscillators Wake-up Sources
clkCPU
clkFLASH
clkIO
clkADC
clkASY
Main Clock
Source Enabled
Timer Oscillator
Enabled
INT1, INT0 and
Pin Change
TWI Address
Match
Timer2
SPM/EEPROM
Ready
ADC
WDT
Other I/O
Idle X X X X X(2) X X X X X X X
ADC noise
Reduction X X X X(2) X(3) X X X X X
Power-down X(3) X X
Power-save X X X(3) X X X
Standby(1) X X(3) X X
Notes: 1. Only recommended with external crystal or resonator selected as clock source.
2. If timer/Ccunter2 is running in asynchronous mode.
3. For INT1 and INT0, only level interrupt.
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5.7.7 Power Reduction Register
The power reduction register, PRR, provides a method to stop the clock to individual peripherals to reduce power
consumption. The current state of the peripheral is frozen and the I/O registers can not be read or written. Resources used
by the peripheral when stopping the clock will remain occupied, hence the peripheral should in most cases be disabled
before stopping the clock. Waking up a module, which is done by clearing the bit in PRR, puts the module in the same state
as before shutdown.
Module shutdown can be used in Idle mode and Active mode to significantly reduce the overall power consumption. See
Section 6.3.1.1 “Power-down Supply Current” on page 281 for examples. In all other sleep modes, the clock is already
stopped.
5.7.7.1 Power Reduction Register - PRR
• Bit 7 - PRTWI: Power Reduction TWI
Writing a logic one to this bit shuts down the TWI by stopping the clock to the module. When waking up the TWI again, the
TWI should be re initialized to ensure proper operation.
• Bit 6 - PRTIM2: Power Reduction Timer/Counter2
Writing a logic one to this bit shuts down the Timer/Counter2 module in synchronous mode (AS2 is 0). When the
Timer/Counter2 is enabled, operation will continue like before the shutdown.
• Bit 5 - PRTIM0: Power Reduction Timer/Counter0
Writing a logic one to this bit shuts down the Timer/Counter0 module. When the Timer/Counter0 is enabled, operation will
continue like before the shutdown.
• Bit 4 - Res: Reserved bit
This bit is reserved in Atmel® ATA6612C/ATA6613C and will always read as zero.
• Bit 3 - PRTIM1: Power Reduction Timer/Counter1
Writing a logic one to this bit shuts down the Timer/Counter1 module. When the Timer/Counter1 is enabled, operation will
continue like before the shutdown.
• Bit 2 - PRSPI: Power Reduction Serial Peripheral Interface
If using debugWIRE on-chip debug system, this bit should not be written to one. Writing a logic one to this bit shuts down the
serial peripheral interface by stopping the clock to the module. When waking up the SPI again, the SPI should be
re-initialized to ensure proper operation.
• Bit 1 - PRUSART0: Power Reduction USART0
Writing a logic one to this bit shuts down the USART by stopping the clock to the module. When waking up the USART
again, the USART should be re-initialized to ensure proper operation.
• Bit 0 - PRADC: Power Reduction ADC
Writing a logic one to this bit shuts down the ADC. The ADC must be disabled before shut down. The analog comparator
cannot use the ADC input MUX when the ADC is shut down.
Bit 7 6 5 4 3 2 1 0
PRTWI PRTIM2 PRTIM0 – PRTIM1 PRSPI PRUSART0 PRADC PRR
Read/Write R/W R/W R/W R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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5.7.8 Minimizing Power Consumption
There are several possibilities to consider when trying to minimize the power consumption in an AVR® controlled system. In
general, sleep modes should be used as much as possible, and the sleep mode should be selected so that as few as
possible of the device’s functions are operating. All functions not needed should be disabled. In particular, the following
modules may need special consideration when trying to achieve the lowest possible power consumption.
5.7.8.1 Analog to Digital Converter
If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be disabled before entering any
sleep mode. When the ADC is turned off and on again, the next conversion will be an extended conversion. Refer to
Section 5.21 “Analog-to-Digital Converter” on page 224 for details on ADC operation.
5.7.8.2 Analog Comparator
When entering Idle mode, the analog comparator should be disabled if not used. When entering ADC noise reduction mode,
the analog comparator should be disabled. In other sleep modes, the analog comparator is automatically disabled. However,
if the analog comparator is set up to use the internal voltage reference as input, the analog comparator should be disabled in
all sleep modes. Otherwise, the internal voltage reference will be enabled, independent of sleep mode. Refer to
Section 5.20 “Analog Comparator” on page 221 for details on how to configure the analog comparator.
5.7.8.3 Brown-out Detector
If the brown-out detector is not needed by the application, this module should be turned off. If the brown-out detector is
enabled by the BODLEVEL fuses, it will be enabled in all sleep modes, and hence, always consume power. In the deeper
sleep modes, this will contribute significantly to the total current consumption. Refer to
Section 5.8.5 “Brown-out Detection” on page 63 for details on how to configure the brown-out detector.
5.7.8.4 Internal Voltage Reference
The internal voltage reference will be enabled when needed by the brown-out detection, the analog comparator or the ADC.
If these modules are disabled as described in the sections above, the internal voltage reference will be disabled and it will
not be consuming power. When turned on again, the user must allow the reference to start up before the output is used. If
the reference is kept on in sleep mode, the output can be used immediately. Refer to Section 5.8.8 “Internal Voltage
Reference” on page 65 for details on the start-up time.
5.7.8.5 Watchdog Timer
If the watchdog timer is not needed in the application, the module should be turned off. If the watchdog timer is enabled, it
will be enabled in all sleep modes and hence always consume power. In the deeper sleep modes, this will contribute
significantly to the total current consumption. Refer to Section 5.8.9 “Watchdog Timer” on page 66 for details on how to
configure the watchdog timer.
5.7.8.6 Port Pins
When entering a sleep mode, all port pins should be configured to use minimum power. The most important is then to ensure
that no pins drive resistive loads. In sleep modes where both the I/O clock (clkI/O) and the ADC clock (clkADC) are stopped,
the input buffers of the device will be disabled. This ensures that no power is consumed by the input logic when not needed.
In some cases, the input logic is needed for detecting wake-up conditions, and it will then be enabled. Refer to the section
Section 5.10.2.5 “Digital Input Enable and Sleep Modes” on page 81 for details on which pins are enabled. If the input buffer
is enabled and the input signal is left floating or have an analog signal level close to VCC/2, the input buffer will use excessive
power.
For analog input pins, the digital input buffer should be disabled at all times. An analog signal level close to VCC/2 on an input
pin can cause significant current even in active mode. Digital input buffers can be disabled by writing to the digital input
disable registers (DIDR1 and DIDR0). Refer to Section 5.20.3.1 “Digital Input Disable Register 1 – DIDR1” on page 223 and
Section 5.21.6.5 “Digital Input Disable Register 0 – DIDR0” on page 238 for details.
5.7.8.7 On-chip Debug System
If the on-chip debug system is enabled by the DWEN fuse and the chip enters sleep mode, the main clock source is enabled
and hence always consumes power. In the deeper sleep modes, this will contribute significantly to the total current
consumption.
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5.8 System Control and Reset
5.8.1 Resetting the AVR
During reset, all I/O registers are set to their initial values, and the program starts execution from the reset vector. For the
Atmel® ATA6613C, the instruction placed at the reset vector must be a JMP – absolute jump – instruction to the reset
handling routine. For the Atmel ATA6612C, the instruction placed at the reset vector must be an RJMP – relative jump –
instruction to the reset handling routine. If the program never enables an interrupt source, the interrupt vectors are not used,
and regular program code can be placed at these locations. This is also the case if the reset vector is in the application
section while the interrupt vectors are in the boot section or vice versa (Atmel ATA6612C/ATA6613C only). The circuit
diagram in Figure 5-15 on page 61 shows the reset logic. Table 5-20 on page 62 defines the electrical parameters of the
reset circuitry.
The I/O ports of the AVR® are immediately reset to their initial state when a reset source goes active. This does not require
any clock source to be running.
After all reset sources have gone inactive, a delay counter is invoked, stretching the internal reset. This allows the power to
reach a stable level before normal operation starts. The time-out period of the delay counter is defined by the user through
the SUT and CKSEL fuses. The different selections for the delay period are presented in
Section 5.6.2 “Clock Sources” on page 47.
5.8.2 Reset Sources
The Atmel ATA6612C/ATA6613C has four sources of reset:
●Power-on reset: The MCU is reset when the supply voltage is below the power-on reset threshold (VPOT).
●External reset: The MCU is reset when a low level is present on the RESET pin for longer than the minimum pulse
length.
●Watchdog system reset: The MCU is reset when the watchdog timer period expires and the watchdog system reset
mode is enabled.
●Brown-out reset: The MCU is reset when the supply voltage VCC is below the brown-out reset threshold (VBOT) and the
brown-out detector is enabled.
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Figure 5-15. Reset Logic
5.8.3 Power-on Reset
A power-on reset (POR) pulse is generated by an on-chip detection circuit. The detection level is defined in
Table 5-20 on page 62. The POR is activated whenever VCC is below the detection level. The POR circuit can be used to
trigger the start-up reset, as well as to detect a failure in supply voltage.
A power-on reset (POR) circuit ensures that the device is reset from power-on. Reaching the power-on reset threshold
voltage invokes the delay counter, which determines how long the device is kept in RESET after VCC rise. The RESET signal
is activated again, without any delay, when VCC decreases below the detection level.
Power-on Reset
Circuit
Brown-out
Reset Circuit
MCU Status
Register (MCUSR)
Reset Circuit
Pull-up Resistor
BODLEVEL [2..0]
SQ
R
DATA BUS
CK
SUT[1:0]
CKSEL[3:0]
RSTDISBL
COUNTER RESET
INTERNAL RESET
TIMEOUT
SPIKE
FILTER
RESET
VCC
Delay Counters
Watchdog
Timer
Watchdog
Oscillator
Clock
Generator
PORF
BORF
WDRF
EXTRF
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Figure 5-16. MCU Start-up, RESET Tied to VCC
Figure 5-17. MCU Start-up, RESET Extended Externally
VCC
INTERNAL
RESET
TIME-OUT
RESET
VPORMAX
VPORMIN
VRST
tTOUT
VCCRR
VCC
INTERNAL
RESET
RESET
TIME-OUT
V
POR
V
RST
t
TOUT
Table 5-20. Power-on Reset Characteristics
Parameter Symbol Min Typ Max Unit
Power-on reset threshold voltage (rising) VPOT
1.0 1.4 V
Power-on reset threshold voltage (falling)(1) 0.9 1.3 V
VCC Max. start voltage to ensure internal power-on reset signal VPORMAX 0.4 V
VCC Min. start voltage to ensure internal power-on reset signal VPORMIN –0.1 V
VCC rise rate to ensure power-on reset VCCRR 0.01 V/ms
RESET pin threshold voltage VRST 0.1 VCC 0.9 VCC V
Minimum pulse width on RESET pin tRST
Note: 1. Before rising, the supply has to be between VPORMIN and VPORMAX to ensure a reset.
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5.8.4 External Reset
An external reset is generated by a low level on the RESET pin. Reset pulses longer than the minimum pulse width (see
Table 5-20 on page 62) will generate a reset, even if the clock is not running. Shorter pulses are not guaranteed to generate
a reset. When the applied signal reaches the reset threshold voltage – VRST – on its positive edge, the delay counter starts
the MCU after the Time-out period – tTOUT – has expired. The external reset can be disabled by the RSTDISBL fuse, see
Table 5-118 on page 255.
Figure 5-18. External Reset During Operation
5.8.5 Brown-out Detection
Atmel® ATA6612C/ATA6613C has an on-chip brown-out detection (BOD) circuit for monitoring the VCC level during
operation by comparing it to a fixed trigger level. The trigger level for the BOD can be selected by the BODLEVEL fuses. The
trigger level has a hysteresis to ensure spike free brown-out detection. The hysteresis on the detection level should be
interpreted as VBOT+ = VBOT + VHYST/2 and VBOT– = VBOT – VHYST/2.
tTOUT
RESET
VCC
INTERNAL
RESET
TIME-OUT
VRST
Table 5-21. BODLEVEL Fuse Coding(1)
BODLEVEL 2..0 Fuses Min VBOT Typ VBOT Max VBOT Units
111 BOD disabled
110 1.8
V101 2.7
100 4.3
011
Reserved
010
001
000
Note: 1. VBOT may be below nominal minimum operating voltage for some devices. For devices where this is the case,
the device is tested down to VCC = VBOT during the production test. This guarantees that a brown-out reset will
occur before VCC drops to a voltage where correct operation of the microcontroller is no longer guaranteed.
The test is performed using BODLEVEL = 110 and BODLEVEL = 101 for Atmel ATA6612CV/ATA6613CV, and
BODLEVEL = 101 and BODLEVEL = 101 for ATA6612C/ATA6613C.
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When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in Figure 5-19), the brown-out reset is
immediately activated. When VCC increases above the trigger level (VBOT+ in Figure 5-19), the delay counter starts the MCU
after the time-out period tTOUT has expired.
The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level for longer than tBOD given in
Table 5-20 on page 62.
Figure 5-19. Brown-out Reset During Operation
5.8.6 Watchdog System Reset
When the watchdog times out, it will generate a short reset pulse of one CK cycle duration. On the falling edge of this pulse,
the delay timer starts counting the time-out period tTOUT. Refer to Section 5.8.9 “Watchdog Timer” on page 66 for details on
operation of the watchdog timer.
Figure 5-20. Watchdog System Reset During Operation
Table 5-22. Brown-out Characteristics
Symbol Parameter Min Typ Max Units
VHYST Brown-out Detector Hysteresis 50 mV
tBOD Min Pulse Width on Brown-out Reset ns
VBOT-
VBOT+
tTOUT
V
CC
RESET
INTERNAL
RESET
TIME-OUT
1 CK Cycle
VCC
RESET
INTERNAL
RESET
RESET
TIME-OUT
WD
TIME-OUT
t
TOUT
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5.8.7 MCU Status Register – MCUSR
The MCU status register provides information on which reset source caused an MCU reset.
• Bit 7..4: Res: Reserved Bits
These bits are unused bits in the Atmel® ATA6612C/ATA6613C, and will always read as zero.
• Bit 3 – WDRF: Watchdog System Reset Flag
This bit is set if a watchdog system reset occurs. The bit is reset by a power-on reset, or by writing a logic zero to the flag.
• Bit 2 – BORF: Brown-out Reset Flag
This bit is set if a brown-out reset occurs. The bit is reset by a power-on reset, or by writing a logic zero to the flag.
• Bit 1 – EXTRF: External Reset Flag
This bit is set if an external reset occurs. The bit is reset by a power-on reset, or by writing a logic zero to the flag.
• Bit 0 – PORF: Power-on Reset Flag
This bit is set if a power-on reset occurs. The bit is reset only by writing a logic zero to the flag.
To make use of the reset flags to identify a reset condition, the user should read and then reset the MCUSR as early as
possible in the program. If the register is cleared before another reset occurs, the source of the reset can be found by
examining the reset flags.
5.8.8 Internal Voltage Reference
Atmel ATA6612C/ATA6613C features an internal band gap reference. This reference is used for brown-out detection, and it
can be used as an input to the analog comparator or the ADC.
5.8.8.1 Voltage Reference Enable Signals and Start-up Time
The voltage reference has a start-up time that may influence the way it should be used. The start-up time is given in
Table 5-23 on page 65. To save power, the reference is not always turned on. The reference is on during the following
situations:
1. When the BOD is enabled (by programming the BODLEVEL [2..0] fuses).
2. When the bandgap reference is connected to the analog comparator (by setting the ACBG bit in ACSR).
3. When the ADC is enabled.
Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user must always allow the
reference to start up before the output from the analog comparator or ADC is used. To reduce power consumption in
power-down mode, the user can avoid the three conditions above to ensure that the reference is turned off before entering
power-down mode.
Bit 76543210
– – – – WDRF BORF EXTRF PORF MCUSR
Read/Write R R R R R/W R/W R/W R/W
Initial Value 0 0 0 0 See Bit Description
Table 5-23. Internal Voltage Reference Characteristics(1)
Parameter Condition Symbol Min Typ Max Units
Bandgap reference voltage TBD VBG 1.0 1.1 1.2 V
Bandgap reference start-up time TBD tBG 40 70 µs
Bandgap reference current consumption TBD IBG 10 TBD µA
Note: 1. Values are guidelines only. Actual values are TBD.
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5.8.9 Watchdog Timer
Atmel® ATA6612C/ATA6613C has an enhanced watchdog timer (WDT). The main features are:
●Clocked from separate on-chip oscillator
●3 operating modes
●Interrupt
●System reset
●Interrupt and system reset
●Selectable time-out period from 16ms to 8s
●Possible hardware fuse watchdog always on (WDTON) for fail-safe mode
Figure 5-21. Watchdog Timer
The watchdog timer (WDT) is a timer counting cycles of a separate on-chip 128kHz oscillator. The WDT gives an interrupt or
a system reset when the counter reaches a given time-out value. In normal operation mode, it is required that the system
uses the WDR - watchdog timer reset - instruction to restart the counter before the time-out value is reached. If the system
doesn't restart the counter, an interrupt or system reset will be issued.
In Interrupt mode, the WDT gives an interrupt when the timer expires. This interrupt can be used to wake the device from
sleep-modes, and also as a general system timer. One example is to limit the maximum time allowed for certain operations,
giving an interrupt when the operation has run longer than expected. In System Reset mode, the WDT gives a reset when
the timer expires. This is typically used to prevent system hang-up in case of runaway code. The third mode, Interrupt and
system reset mode, combines the other two modes by first giving an interrupt and then switch to system reset mode. This
mode will for instance allow a safe shutdown by saving critical parameters before a system reset.
OSC/64K
OSC/16K
OSC/2K
OSC/4K
OSC/8K
OSC/32K
OSC/128K
OSC/256K
OSC/512K
OSC/1024K
Watchdog
Prescaler
WDP0
WDE
WATCHDOG
RESET
WDIF
WDIE
WDP1
WDP2
WDP3
MCU RESET
INTERRUPT
128kHz
Oscillator
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The watchdog always on (WDTON) fuse, if programmed, will force the watchdog timer to system reset mode. With the fuse
programmed the system reset mode bit (WDE) and Interrupt mode bit (WDIE) are locked to 1 and 0 respectively. To further
ensure program security, alterations to the Watchdog set-up must follow timed sequences. The sequence for clearing WDE
and changing time-out configuration is as follows:
1. In the same operation, write a logic one to the watchdog change enable bit (WDCE) and WDE. A logic one must
be written to WDE regardless of the previous value of the WDE bit.
2. Within the next four clock cycles, write the WDE and watchdog prescaler bits (WDP) as desired, but with the
WDCE bit cleared. This must be done in one operation.
The following code example shows one assembly and one C function for turning off the watchdog timer. The example
assumes that interrupts are controlled (e.g. by disabling interrupts globally) so that no interrupts will occur during the
execution of these functions.
Notes: 1. The example code assumes that the part specific header file is included.
2. If the watchdog is accidentally enabled, for example by a runaway pointer or brown-out condition, the device
will be reset and the watchdog timer will stay enabled. If the code is not set up to handle the watchdog, this
might lead to an eternal loop of time-out resets. To avoid this situation, the application software should always
clear the watchdog system reset flag (WDRF) and the WDE control bit in the initialization routine, even if the
watchdog is not in use.
Assembly Code Example(1)
WDT_off:
; Turn off global interrupt
cli
; Reset Watchdog Timer
wdr
; Clear WDRF in MCUSR
in r16, MCUSR
andi r16, (0xff & (0<<WDRF))
out MCUSR, r16
; Write logical one to WDCE and WDE
; Keep old prescaler setting to prevent unintentional time-out
lds r16, WDTCSR
ori r16, (1<<WDCE) | (1<<WDE)
sts WDTCSR, r16
; Turn off WDT
ldi r16, (0<<WDE)
sts WDTCSR, r16
; Turn on global interrupt
sei
ret
C Code Example(1)
void WDT_off(void)
{
__disable_interrupt();
__watchdog_reset();
/* Clear WDRF in MCUSR */
MCUSR &= ~(1<<WDRF);
/* Write logical one to WDCE and WDE */
/* Keep old prescaler setting to prevent unintentional time-
out */
WDTCSR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCSR = 0x00;
__enable_interrupt();
}
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The following code example shows one assembly and one C function for changing the time-out value of the watchdog timer.
Notes: 1. The example code assumes that the part specific header file is included.
2. The watchdog timer should be reset before any change of the WDP bits, since a change in the WDP bits can
result in a time-out when switching to a shorter time-out period.
5.8.9.1 Watchdog Timer Control Register - WDTCSR
• Bit 7 - WDIF: Watchdog Interrupt Flag
This bit is set when a time-out occurs in the watchdog timer and the watchdog timer is configured for interrupt. WDIF is
cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, WDIF is cleared by writing a
logic one to the flag. When the I-bit in SREG and WDIE are set, the watchdog time-out interrupt is executed.
• Bit 6 - WDIE: Watchdog Interrupt Enable
When this bit is written to one and the I-bit in the status register is set, the watchdog interrupt is enabled. If WDE is cleared in
combination with this setting, the watchdog timer is in interrupt mode, and the corresponding interrupt is executed if time-out
in the watchdog timer occurs.
If WDE is set, the watchdog timer is in interrupt and system reset mode. The first time-out in the watchdog timer will set
WDIF. Executing the corresponding interrupt vector will clear WDIE and WDIF automatically by hardware (the watchdog
goes to system reset mode). This is useful for keeping the watchdog timer security while using the interrupt. To stay in
interrupt and system reset mode, WDIE must be set after each interrupt. This should however not be done within the
interrupt service routine itself, as this might compromise the safety-function of the watchdog system reset mode. If the
interrupt is not executed before the next time-out, a system reset will be applied.
Assembly Code Example(1)
WDT_Prescaler_Change:
; Turn off global interrupt
cli
; Reset Watchdog Timer
wdr
; Start timed sequence
lds r16, WDTCSR
ori r16, (1<<WDCE) | (1<<WDE)
sts WDTCSR, r16
; -- Got four cycles to set the new values from here -
; Set new prescaler(time-out) value = 64K cycles (~0.5 s)
ldi r16, (1<<WDE) | (1<<WDP2) | (1<<WDP0)
sts WDTCSR, r16
; -- Finished setting new values, used 2 cycles -
; Turn on global interrupt
sei
ret
C Code Example(1)
void WDT_Prescaler_Change(void)
{
__disable_interrupt();
__watchdog_reset();
/* Start timed equence */
WDTCSR |= (1<<WDCE) | (1<<WDE);
/* Set new prescaler(time-out) value = 64K cycles (~0.5 s) */
WDTCSR = (1<<WDE) | (1<<WDP2) | (1<<WDP0);
__enable_interrupt();
}
Bit 76543210
WDIF WDIE WDP3 WDCE WDE WDP2 WDP1 WDP0 WDTCSR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value0000X000
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• Bit 4 - WDCE: Watchdog Change Enable
This bit is used in timed sequences for changing WDE and prescaler bits. To clear the WDE bit, and/or change the prescaler
bits, WDCE must be set.
Once written to one, hardware will clear WDCE after four clock cycles.
• Bit 3 - WDE: Watchdog System Reset Enable
WDE is overridden by WDRF in MCUSR. This means that WDE is always set when WDRF is set. To clear WDE, WDRF
must be cleared first. This feature ensures multiple resets during conditions causing failure, and a safe start-up after the
failure.
• Bit 5, 2..0 - WDP3..0: Watchdog Timer Prescaler 3, 2, 1 and 0
The WDP3..0 bits determine the watchdog timer prescaling when the watchdog timer is running. The different prescaling
values and their corresponding time-out periods are shown in Table 5-25.
Table 5-24. Watchdog Timer Configuration
WDTON WDE WDIE Mode Action on Time-out
0 0 0 Stopped None
0 0 1 Interrupt mode Interrupt
0 1 0 System reset mode Reset
0 1 1 Interrupt and system reset mode Interrupt, then go to system reset
Mode
1 x x System reset mode Reset
Table 5-25. Watchdog Timer Prescale Select
WDP3 WDP2 WDP1 WDP0 Number of WDT Oscillator Cycles
Typical Time-out at
VCC = 5.0V
0 0 0 0 2K (2048) cycles 16ms
0 0 0 1 4K (4096) cycles 32ms
0 0 1 0 8K (8192) cycles 64ms
0 0 1 1 16K (16384) cycles 0.125s
0 1 0 0 32K (32768) cycles 0.25s
0 1 0 1 64K (65536) cycles 0.5s
0 1 1 0 128K (131072) cycles 1.0s
0 1 1 1 256K (262144) cycles 2.0s
1 0 0 0 512K (524288) cycles 4.0s
1 0 0 1 1024K (1048576) cycles 8.0s
1 0 1 0
Reserved
1 0 1 1
1 1 0 0
1 1 0 1
1 1 1 0
1 1 1 1
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5.9 Interrupts
This section describes the specifics of the interrupt handling as performed in Atmel® ATA6612C/ATA6613C. For a general
explanation of the AVR® interrupt handling, refer to Section 5.4.8 “Reset and Interrupt Handling” on page 36.
The interrupt vectors in Atmel ATA6612C and ATA6613C are generally the same, with the following differences:
●Each interrupt vector occupies two instruction words in ATA6613C, and one instruction word in Atmel ATA6612C.
●In Atmel ATA6612C and ATA6613C, the reset vector is affected by the BOOTRST fuse, and the Interrupt vector start
address is affected by the IVSEL bit in MCUCR.
5.9.1 Interrupt Vectors in Atmel ATA6612C
Table 5-26. Reset and Interrupt Vectors in Atmel ATA6612C
Vector No. Program Address(2) Source Interrupt Definition
10x000(1) RESET External pin, power-on reset, brown-out reset and watchdog
system reset
20x001 INT0 External interrupt request 0
30x002 INT1 External interrupt request 1
40x003 PCINT0 Pin change interrupt request 0
50x004 PCINT1 Pin change interrupt request 1
60x005 PCINT2 Pin change interrupt request 2
70x006 WDT Watchdog time-out interrupt
80x007 TIMER2 COMPA Timer/Counter2 compare match A
90x008 TIMER2 COMPB Timer/Counter2 compare match B
10 0x009 TIMER2 OVF Timer/Counter2 overflow
11 0x00A TIMER1 CAPT Timer/Counter1 capture event
12 0x00B TIMER1 COMPA Timer/Counter1 compare match A
13 0x00C TIMER1 COMPB Timer/coutner1 compare match B
14 0x00D TIMER1 OVF Timer/Counter1 overflow
15 0x00E TIMER0 COMPA Timer/Counter0 compare match A
16 0x00F TIMER0 COMPB Timer/Counter0 compare match B
17 0x010 TIMER0 OVF Timer/Counter0 overflow
18 0x011 SPI, STC SPI serial transfer complete
19 0x012 USART, RX USART Rx complete
20 0x013 USART, UDRE USART, data register empty
21 0x014 USART, TX USART, Tx complete
22 0x015 ADC ADC conversion complete
23 0x016 EE READY EEPROM ready
24 0x017 ANALOG COMP Analog comparator
25 0x018 TWI 2-wire serial interface
26 0x019 SPM READY Store program memory ready
Notes: 1. When the BOOTRST fuse is programmed, the device will jump to the boot loader address at reset (see
Section 5.23 “Boot Loader Support – Read-While-Write Self-Programming, Atmel ATA6612C and ATA6613C”
on page 240).
2. When the IVSEL bit in MCUCR is set, Interrupt vectors will be moved to the start of the boot flash section. The
address of each interrupt vector will then be the address in this table added to the start address of the boot
flash section.
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Table 5-27 shows reset and interrupt vectors placement for the various combinations of BOOTRST and IVSEL settings. If the
program never enables an interrupt source, the interrupt vectors are not used, and regular program code can be placed at
these locations. This is also the case if the reset vector is in the application section while the interrupt vectors are in the boot
section or vice versa.
The most typical and general program setup for the reset and interrupt vector addresses in Atmel ATA6612C is:
Address Labels Code Comments
0x000 rjmp RESET ; Reset Handler
0x001 rjmp EXT_INT0 ; IRQ0 Handler
0x002 rjmp EXT_INT1 ; IRQ1 Handler
0x003 rjmp PCINT0 ; PCINT0 Handler
0x004 rjmp PCINT1 ; PCINT1 Handler
0x005 rjmp PCINT2 ; PCINT2 Handler
0x006 rjmp WDT ; Watchdog Timer Handler
0x007 rjmp TIM2_COMPA ; Timer2 Compare A Handler
0X008 rjmp TIM2_COMPB ; Timer2 Compare B Handler
0x009 rjmp TIM2_OVF ; Timer2 Overflow Handler
0x00A rjmp TIM1_CAPT ; Timer1 Capture Handler
0x00B rjmp TIM1_COMPA ; Timer1 Compare A Handler
0x00C rjmp TIM1_COMPB ; Timer1 Compare B Handler
0x00D rjmp TIM1_OVF ; Timer1 Overflow Handler
0x00E rjmp TIM0_COMPA ; Timer0 Compare A Handler
0x00F rjmp TIM0_COMPB ; Timer0 Compare B Handler
0x010 rjmp TIM0_OVF ; Timer0 Overflow Handler
0x011 rjmp SPI_STC ; SPI Transfer Complete Handler
0x012 rjmp USART_RXC ; USART, RX Complete Handler
0x013 rjmp USART_UDRE ; USART, UDR Empty Handler
0x014 rjmp USART_TXC ; USART, TX Complete Handler
0x015 rjmp ADC ; ADC Conversion Complete Handler
0x016 rjmp EE_RDY ; EEPROM Ready Handler
0x017 rjmp ANA_COMP ; Analog Comparator Handler
0x018 rjmp TWI ; 2-wire Serial Interface Handler
0x019 rjmp SPM_RDY ; Store Program Memory Ready Handler
;
0x01A RESET: ldi r16, high(RAMEND); Main program start
0x01B out SPH,r16 ; Set Stack Pointer to top of RAM
0x01C ldi r16, low(RAMEND)
0x01D out SPL,r16
0x01E sei ; Enable interrupts
0x01F <instr> xxx
... ... ... ...
Table 5-27. Reset and Interrupt Vectors Placement in Atmel ATA6612C(1)
BOOTRST IVSEL Reset Address Interrupt Vectors Start Address
1 0 0x000 0x001
1 1 0x000 Boot reset address + 0x001
0 0 Boot reset address 0x001
0 1 Boot reset address Boot reset address + 0x001
Note: 1. The Boot Reset Address is shown in Table 5-108 on page 251. For the BOOTRST Fuse “1” means unpro-
grammed while “0” means programmed.
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When the BOOTRST Fuse is unprogrammed, the boot section size set to 2Kbytes and the IVSEL bit in the MCUCR register
is set before any interrupts are enabled, the most typical and general program setup for the reset and interrupt vector
addresses in Atmel® ATA6612C is:
Address Labels Code Comments
0x000 RESET: ldi r16,high(RAMEND); Main program start
0x001 out SPH,r16 ; Set Stack Pointer to top of RAM
0x002 ldi r16,low(RAMEND)
0x003 out SPL,r16
0x004 sei ; Enable interrupts
0x005 <instr> xxx
;
.org 0xC01
0xC01 rjmp EXT_INT0 ; IRQ0 Handler
0xC02 rjmp EXT_INT1 ; IRQ1 Handler
... ... ... ;
0xC19 rjmp SPM_RDY ; Store Program Memory Ready Handler
When the BOOTRST fuse is programmed and the boot section size set to 2Kbytes, the most typical and general program
setup for the reset and Interrupt vector Aadresses in Atmel ATA6612C is:
Address Labels Code Comments
.org 0x001
0x001 rjmp EXT_INT0 ; IRQ0 Handler
0x002 rjmp EXT_INT1 ; IRQ1 Handler
... ... ... ;
0x019 rjmp SPM_RDY ; Store Program Memory Ready Handler
;
.org 0xC00
0xC00 RESET: ldi r16,high(RAMEND); Main program start
0xC01 out SPH,r16; Set Stack Pointer to top of RAM
0xC02 ldi r16,low(RAMEND)
0xC03 out SPL,r16
0xC04 sei ; Enable interrupts
0xC05 <instr> xxx
When the BOOTRST fuse is programmed, the boot section size set to 2Kbytes and the IVSEL bit in the MCUCR register is
set before any interrupts are enabled, the most typical and general program setup for the reset and interrupt vector
addresses in Atmel ATA6612C is:
Address Labels Code Comments
;
.org 0xC00
0xC00 rjmp RESET; Reset handler
0xC01 rjmp EXT_INT0; IRQ0 Handler
0xC02 rjmp EXT_INT1; IRQ1 Handler
... ... ... ;
0xC19 rjmp SPM_RDY; Store Program Memory Ready Handler
;
0xC1A RESET: ldi r16,high(RAMEND); Main program start
0xC1B out SPH,r16 ; Set Stack Pointer to top of RAM
0xC1C ldi r16,low(RAMEND)
0xC1D out SPL,r16
0xC1E sei ; Enable interrupts
0xC1F <instr> xxx
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5.9.2 Interrupt Vectors in ATA6613C
Table 5-28. Reset and Interrupt Vectors in ATA6613C
Vector No.
Program
Address(2) Source Interrupt Definition
10x0000(1) RESET External pin, power-on reset, brown-out reset and watchdog
system reset
20x0002 INT0 External interrupt request 0
30x0004 INT1 External interrupt request 1
40x0006 PCINT0 Pin change interrupt request 0
50x0008 PCINT1 Pin change interrupt request 1
60x000A PCINT2 Pin change interrupt request 2
70x000C WDT Watchdog time-out interrupt
80x000E TIMER2 COMPA Timer/Counter2 compare match A
90x0010 TIMER2 COMPB Timer/Counter2 compare match B
10 0x0012 TIMER2 OVF Timer/Counter2 overflow
11 0x0014 TIMER1 CAPT Timer/Counter1 capture event
12 0x0016 TIMER1 COMPA Timer/Counter1 compare match A
13 0x0018 TIMER1 COMPB Timer/coutner1 compare match B
14 0x001A TIMER1 OVF Timer/Counter1 overflow
15 0x001C TIMER0 COMPA Timer/Counter0 compare match A
16 0x001E TIMER0 COMPB Timer/Counter0 compare match B
17 0x0020 TIMER0 OVF Timer/Counter0 overflow
18 0x0022 SPI, STC SPI serial transfer complete
19 0x0024 USART, RX USART Rx complete
20 0x0026 USART, UDRE USART, data register empty
21 0x0028 USART, TX USART, Tx complete
22 0x002A ADC ADC conversion complete
23 0x002C EE READY EEPROM ready
24 0x002E ANALOG COMP Analog comparator
25 0x0030 TWI 2-wire serial interface
26 0x0032 SPM READY Store program memory ready
Notes: 1. When the BOOTRST Fuse is programmed, the device will jump to the boot loader address at reset (see Sec-
tion 5.23 “Boot Loader Support – Read-While-Write Self-Programming, Atmel ATA6612C and ATA6613C” on
page 240).
2. When the IVSEL bit in MCUCR is set, interrupt vectors will be moved to the start of the boot flash section. The
address of each interrupt vector will then be the address in this table added to the start address of the boot
flash section.
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Table 5-29 shows reset and interrupt vectors placement for the various combinations of BOOTRST and IVSEL settings. If the
program never enables an interrupt source, the interrupt vectors are not used, and regular program code can be placed at
these locations. This is also the case if the reset vector is in the application section while the interrupt vectors are in the boot
section or vice versa.
The most typical and general program setup for the reset and interrupt vector addresses in ATA6613C is:
Address Labels Code Comments
0x0000 rjmp RESET ; Reset Handler
0x0002 rjmp EXT_INT0 ; IRQ0 Handler
0x0004 rjmp EXT_INT1 ; IRQ1 Handler
0x0006 rjmp PCINT0 ; PCINT0 Handler
0x0008 rjmp PCINT1 ; PCINT1 Handler
0x000A rjmp PCINT2 ; PCINT2 Handler
0x000C rjmp WDT ; Watchdog Timer Handler
0x000E rjmp TIM2_COMPA ; Timer2 Compare A Handler
0x0010 rjmp TIM2_COMPB ; Timer2 Compare B Handler
0x0012 rjmp TIM2_OVF ; Timer2 Overflow Handler
0x0014 rjmp TIM1_CAPT ; Timer1 Capture Handler
0x0016 rjmp TIM1_COMPA ; Timer1 Compare A Handler
0x0018 rjmp TIM1_COMPB ; Timer1 Compare B Handler
0x001A rjmp TIM1_OVF ; Timer1 Overflow Handler
0x001C rjmp TIM0_COMPA ; Timer0 Compare A Handler
0x001E rjmp TIM0_COMPB ; Timer0 Compare B Handler
0x0020 rjmp TIM0_OVF ; Timer0 Overflow Handler
0x0022 rjmp SPI_STC ; SPI Transfer Complete Handler
0x0024 rjmp USART_RXC ; USART, RX Complete Handler
0x0026 rjmp USART_UDRE ; USART, UDR Empty Handler
0x0028 rjmp USART_TXC ; USART, TX Complete Handler
0x002A rjmp ADC ; ADC Conversion Complete Handler
0x002C rjmp EE_RDY ; EEPROM Ready Handler
0x002E rjmp ANA_COMP ; Analog Comparator Handler
0x0030 rjmp TWI ; 2-wire Serial Interface Handler
0x0032 rjmp SPM_RDY ; Store Program Memory Ready Handler
;
0x0033 RESET: ldi r16, high(RAMEND); Main program start
0x0034 out SPH,r16 ; Set Stack Pointer to top of RAM
0x0035 ldi r16, low(RAMEND)
0x0036 out SPL,r16
0x0037 sei ; Enable interrupts
0x0038 <instr> xxx
... ... ... ...
Table 5-29. Reset and Interrupt Vectors Placement in ATA6613C(1)
BOOTRST IVSEL Reset Address Interrupt Vectors Start Address
1 0 0x000 0x001
1 1 0x000 Boot reset address + 0x0002
0 0 Boot reset address 0x001
0 1 Boot reset address Boot reset address + 0x0002
Note: 1. The Boot Reset Address is shown in Table 5-108 on page 251. For the BOOTRST fuse “1” means
unprogrammed while “0” means programmed.
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When the BOOTRST Fuse is unprogrammed, the boot section size set to 2K bytes and the IVSEL bit in the MCUCR register
is set before any interrupts are enabled, the most typical and general program setup for the reset and interrupt vector
addresses in ATA6613C is:
Address Labels Code Comments
0x0000 RESET: ldi r16,high(RAMEND); Main program start
0x0001 out SPH,r16 ; Set Stack Pointer to top of RAM
0x0002 ldi r16,low(RAMEND)
0x0003 out SPL,r16
0x0004 sei ; Enable interrupts
0x0005 <instr> xxx
;
.org 0xC02
0x1C02 rjmp EXT_INT0 ; IRQ0 Handler
0x1C04 rjmp EXT_INT1 ; IRQ1 Handler
... ... ... ;
0x1C32 rjmp SPM_RDY ; Store Program Memory Ready Handler
When the BOOTRST fuse is programmed and the boot section size set to 2Kbytes, the most typical and general program
setup for the reset and interrupt vector addresses in ATA6613C is:
Address Labels Code Comments
.org 0x0002
0x0002 rjmp EXT_INT0 ; IRQ0 Handler
0x0004 rjmp EXT_INT1 ; IRQ1 Handler
... ... ... ;
0x0032 rjmp SPM_RDY ; Store Program Memory Ready Handler
;
.org 0x1C00
0x1C00 RESET: ldi r16,high(RAMEND); Main program start
0x1C01 out SPH,r16 ; Set Stack Pointer to top of RAM
0x1C02 ldi r16,low(RAMEND)
0x1C03 out SPL,r16
0x1C04 sei ; Enable interrupts
0x1C05 <instr> xxx
When the BOOTRST fuse is programmed, the boot section size set to 2Kbytes and the IVSEL bit in the MCUCR register is
set before any interrupts are enabled, the most typical and general program setup for the reset and interrupt vector
addresses in ATA6613C is:
Address Labels Code Comments
;
.org 0x1C00
0x1C00 rjmp RESET ; Reset handler
0x1C02 rjmp EXT_INT0 ; IRQ0 Handler
0x1C04 rjmp EXT_INT1 ; IRQ1 Handler
... ... ... ;
0x1C32 rjmp SPM_RDY ; Store Program Memory Ready Handler
;
0x1C33 RESET: ldi r16,high(RAMEND); Main program start
0x1C34 out SPH,r16 ; Set Stack Pointer to top of RAM
0x1C35 ldi r16,low(RAMEND)
0x1C36 out SPL,r16
0x1C37 sei ; Enable interrupts
0x1C38 <instr> xxx
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5.9.2.1 Moving Interrupts Between Application and Boot Space, Atmel ATA6612C and ATA6613C
The MCU control register controls the placement of the interrupt vector table.
5.9.2.2 MCU Control Register – MCUCR
• Bit 1 – IVSEL: Interrupt Vector Select
When the IVSEL bit is cleared (zero), the interrupt vectors are placed at the start of the flash memory. When this bit is set
(one), the interrupt vectors are moved to the beginning of the boot loader section of the flash. The actual address of the start
of the boot flash section is determined by the BOOTSZ fuses. Refer to section Section 5.23 “Boot Loader Support – Read-
While-Write Self-Programming, Atmel ATA6612C and ATA6613C” on page 240 for details. To avoid unintentional changes of
interrupt vector tables, a special write procedure must be followed to change the IVSEL bit:
a. Write the interrupt vector change enable (IVCE) bit to one.
b. Within four cycles, write the desired value to IVSEL while writing a zero to IVCE.
Interrupts will automatically be disabled while this sequence is executed. Interrupts are disabled in the cycle IVCE is
set, and they remain disabled until after the instruction following the write to IVSEL. If IVSEL is not written, interrupts
remain disabled for four cycles. The I-bit in the status register is unaffected by the automatic disabling.
Note: If interrupt vectors are placed in the boot loader section and boot lock bit BLB02 is programmed, interrupts are
disabled while executing from the application section. If interrupt vectors are placed in the application section
and boot lock bit BLB12 is programed, interrupts are disabled while executing from the boot loader section.
Refer to Section 5.23 “Boot Loader Support – Read-While-Write Self-Programming, Atmel ATA6612C and
ATA6613C” on page 240 for details on boot lock bits.
• Bit 0 – IVCE: Interrupt Vector Change Enable
The IVCE bit must be written to logic one to enable change of the IVSEL bit. IVCE is cleared by hardware four cycles after it
is written or when IVSEL is written. Setting the IVCE bit will disable interrupts, as explained in the IVSEL description above.
See code example below.
Bit 76543210
–––PUD –– IVSEL IVCE MCUCR
Read/Write R R R R/W R R R/W R/W
Initial Value00000000
Assembly Code Example
Move_interrupts:
; Enable change of Interrupt Vectors
ldi r16, (1<<IVCE)
out MCUCR, r16
; Move interrupts to Boot Flash section
ldi r16, (1<<IVSEL)
out MCUCR, r16
ret
C Code Example
void Move_interrupts(void)
{
/* Enable change of Interrupt Vectors */
MCUCR = (1<<IVCE);
/* Move interrupts to Boot Flash section */
MCUCR = (1<<IVSEL);
}
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5.10 I/O-Ports
5.10.1 Introduction
All AVR® ports have true read-modify-write functionality when used as general digital I/O ports. This means that the direction
of one port pin can be changed without unintentionally changing the direction of any other pin with the SBI and CBI
instructions. The same applies when changing drive value (if configured as output) or enabling/disabling of pull-up resistors
(if configured as input). Each output buffer has symmetrical drive characteristics with both high sink and source capability.
The pin driver is strong enough to drive LED displays directly. All port pins have individually selectable pull-up resistors with
a supply-voltage invariant resistance. All I/O pins have protection diodes to both VCC and ground as indicated in Figure 5-22.
Refer to Section 5.25 “Electrical Characteristics” on page 271 for a complete list of parameters.
Figure 5-22. I/O Pin Equivalent Schematic
All registers and bit references in this section are written in general form. A lower case “x” represents the numbering letter for
the port, and a lower case “n” represents the bit number. However, when using the register or bit defines in a program, the
precise form must be used. For example, PORTB3 for bit no. 3 in Port B, here documented generally as PORTxn. The
physical I/O registers and bit locations are listed in Section 5.10.4 “Register Description for I/O Ports” on page 91.
Three I/O memory address locations are allocated for each port, one each for the data register – PORTx, data direction
register – DDRx, and the port input pins – PINx. The port input Pins I/O location is read only, while the data register and the
data direction register are read/write. However, writing a logic one to a bit in the PINx register, will result in a toggle in the
corresponding bit in the data register. In addition, the pull-up disable – PUD bit in MCUCR disables the pull-up function for all
pins in all ports when set.
Using the I/O port as general digital I/O is described in Section 5.10.2 “Ports as General Digital I/O” on page 78. Most port
pins are multiplexed with alternate functions for the peripheral features on the device. How each alternate function interferes
with the port pin is described in Section 5.10.3 “Alternate Port Functions” on page 81. Refer to the individual module sections
for a full description of the alternate functions.
Note that enabling the alternate function of some of the port pins does not affect the use of the other pins in the port as
general digital I/O.
Cpin
Rpu
Pxn
Logic
See Figure
”General Digital I/O”
for Details
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5.10.2 Ports as General Digital I/O
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 5-23 shows a functional description of one
I/O-port pin, here generically called Pxn.
Figure 5-23. General Digital I/O(1)
Note: 1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O, SLEEP, and PUD
are common to all ports.
5.10.2.1 Configuring the Pin
Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in Section 5.10.4 “Register Description
for I/O Ports” on page 91, the DDxn bits are accessed at the DDRx I/O address, the PORTxn bits at the PORTx I/O address,
and the PINxn bits at the PINx I/O address.
The DDxn bit in the DDRx register selects the direction of this pin. If DDxn is written logic one, Pxn is configured as an output
pin. If DDxn is written logic zero, Pxn is configured as an input pin.
If PORTxn is written logic one when the pin is configured as an input pin, the pull-up resistor is activated. To switch the
pull-up resistor off, PORTxn has to be written logic zero or the pin has to be configured as an output pin. The port pins are tri-
stated when reset condition becomes active, even if no clocks are running.
If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven high (one). If PORTxn is
written logic zero when the pin is configured as an output pin, the port pin is driven low (zero).
D
0
1
Q
WRx
RRx
WPx
Pnx
CLR
RESET
Synchronizer
DATA BUS
PORTxn
Q
Q
L
D
Q
QD
Q
PINxn
RESET
RPx
WDx: WRITE DDRx
WRx:
WPx:
RPx:
RRx: READ PORTx REGISTER
READ PORTx PIN
WRITE PINx REGISTER
RDx:
WRITE PORTx
READ DDRx
PUD: PULLUP DISABLE
CLKI/O:
SLEEP:
I/O CLOCK
SLEEP CONTROL
RDx
CLKI/O
PUD
WDx
SLEEP
D
QCLR
DDxn
Q
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5.10.2.2 Toggling the Pin
Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn. Note that the SBI instruction
can be used to toggle one single bit in a port.
5.10.2.3 Switching Between Input and Output
When switching between tri-state ({DDxn, PORTxn} = 0b00) and output high ({DDxn, PORTxn} = 0b11), an intermediate
state with either pull-up enabled {DDxn, PORTxn} = 0b01) or output low ({DDxn, PORTxn} = 0b10) must occur. Normally, the
pull-up enabled state is fully acceptable, as a high-impedant environment will not notice the difference between a strong high
driver and a pull-up. If this is not the case, the PUD bit in the MCUCR register can be set to disable all pull-ups in all ports.
Switching between input with pull-up and output low generates the same problem. The user must use either the tri-state
({DDxn, PORTxn} = 0b00) or the output high state ({DDxn, PORTxn} = 0b11) as an intermediate step.
Table 5-30 summarizes the control signals for the pin value.
5.10.2.4 Reading the Pin Value
Independent of the setting of data direction bit DDxn, the port pin can be read through the PINxn register bit. As shown in
Figure 5-23 on page 78, the PINxn register bit and the preceding latch constitute a synchronizer. This is needed to avoid
metastability if the physical pin changes value near the edge of the internal clock, but it also introduces a delay. Figure 5-24
shows a timing diagram of the synchronization when reading an externally applied pin value. The maximum and minimum
propagation delays are denoted tpd,max and tpd,min respectively.
Figure 5-24. Synchronization when Reading an Externally Applied Pin Value
Consider the clock period starting shortly after the first falling edge of the system clock. The latch is closed when the clock is
low, and goes transparent when the clock is high, as indicated by the shaded region of the “SYNC LATCH” signal. The signal
value is latched when the system clock goes low. It is clocked into the PINxn register at the succeeding positive clock edge.
As indicated by the two arrows tpd,max and tpd,min, a single signal transition on the pin will be delayed between ½ and 1½
system clock period depending upon the time of assertion.
Table 5-30. Port Pin Configurations
DDxn PORTxn
PUD
(in MCUCR) I/O Pull-up Comment
0 0 X Input No Tri-state (hi-Z)
0 1 0 Input Yes Pxn will source current if ext. pulled low.
0 1 1 Input No Tri-state (hi-Z)
1 0 X Output No Output low (sink)
1 1 X Output No Output high (source)
SYSTEM CLK
INSTRUCTIONS
SYNC LATCH
PINxn
r17
XXX XXX
0x00 0xFF
in r17, PINx
tpd, max
tpd, min
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When reading back a software assigned pin value, a nop instruction must be inserted as indicated in Figure 5-25. The out
instruction sets the “SYNC LATCH” signal at the positive edge of the clock. In this case, the delay tpd through the
synchronizer is 1 system clock period.
Figure 5-25. Synchronization when Reading a Software Assigned Pin Value
The following code example shows how to set port B pins 0 and 1 high, 2 and 3 low, and define the port pins from 4 to 7 as
input with pull-ups assigned to port pins 6 and 7. The resulting pin values are read back again, but as previously discussed,
a nop instruction is included to be able to read back the value recently assigned to some of the pins.
Note: 1. For the assembly program, two temporary registers are used to minimize the time from pull-ups are set on pins
0, 1, 6, and 7, until the direction bits are correctly set, defining bit 2 and 3 as low and redefining bits 0 and 1 as
strong high drivers.
Assembly Code Example(1)
...
; Define pull-ups and set outputs high
; Define directions for port pins
ldi r16,(1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0)
ldi r17,(1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0)
out PORTB,r16
out DDRB,r17
; Insert nop for synchronization
nop
; Read port pins
in r16,PINB
...
C Code Example
unsigned char i;
...
/* Define pull-ups and set outputs high */
/* Define directions for port pins */
PORTB = (1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0);
DDRB = (1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0);
/* Insert nop for synchronization*/
__no_operation();
/* Read port pins */
i = PINB;
...
SYSTEM CLK
INSTRUCTIONS
SYNC LATCH
PINxn
r16
r17
out PORTx, r16 nop
0x00 0xFF
0xFF
in r17, PINx
tpd
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5.10.2.5 Digital Input Enable and Sleep Modes
As shown in Figure 5-23 on page 78, the digital input signal can be clamped to ground at the input of the Schmitt trigger. The
signal denoted SLEEP in the figure, is set by the MCU sleep controller in power-down mode, power-save mode, and standby
mode to avoid high power consumption if some input signals are left floating, or have an analog signal level close to VCC/2.
SLEEP is overridden for port pins enabled as external interrupt pins. If the external interrupt request is not enabled, SLEEP
is active also for these pins. SLEEP is also overridden by various other alternate functions as described in Section 5.10.3
“Alternate Port Functions” on page 81.
If a logic high level (“one”) is present on an asynchronous external interrupt pin configured as “interrupt on rising edge, falling
edge, or any logic change on pin” while the external interrupt is not enabled, the corresponding external interrupt flag will be
set when resuming from the above mentioned sleep mode, as the clamping in these sleep mode produces the requested
logic change.
5.10.2.6 Unconnected Pins
If some pins are unused, it is recommended to ensure that these pins have a defined level. Even though most of the digital
inputs are disabled in the deep sleep modes as described above, floating inputs should be avoided to reduce current
consumption in all other modes where the digital inputs are enabled (reset, active mode and idle mode).
The simplest method to ensure a defined level of an unused pin, is to enable the internal pull-up. In this case, the pull-up will
be disabled during reset. If low power consumption during reset is important, it is recommended to use an external pull-up or
pull-down. Connecting unused pins directly to VCC or GND is not recommended, since this may cause excessive currents if
the pin is accidentally configured as an output.
5.10.3 Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. Figure 5-26 on page 82 shows how the port
pin control signals from the simplified Figure 5-23 on page 78 can be overridden by alternate functions. The overriding
signals may not be present in all port pins, but the figure serves as a generic description applicable to all port pins in the
AVR® microcontroller family.
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Figure 5-26. Alternate Port Functions(1)
Note: 1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O, SLEEP, and PUD
are common to all ports. All other signals are unique for each pin.
D
0
1
Q
WRx
RRx
WPx
PTOExn
Pnx
CLR
CLR
SET
CLR
RESET
Synchronizer
DATA BUS
PORTxn
Q
0
1
Q
L
D
Q
QD
Q
PINxn
0
1
RESET
RPx
Pxn PULL-UP OVERRIDE ENABLE
Pxn PULL-UP OVERRIDE VALUE
PUD: PULL-UP DISABLEPUOExn:
Pxn PORT VALUE OVERRIDE VALUEPVOVxn:
Pxn PORT VALUE OVERRIDE ENABLEPVOExn:
Pxn DATA DIRECTION OVERRIDE ENABLE
Pxn DATA DIRECTION OVERRIDE VALUE
DDOExn:
DDOVxn:
SLEEP CONTROLSLEEP:
Pxn, PORT TOGGLE OVERRIDE ENABLEPTOExn:
Pxn DIGITAL INPUT ENABLE OVERRIDE VALUEDIEOVxn:
Pxn DIGITAL INPUT ENABLE OVERRIDE ENABLEDIEOExn:
I/O CLOCK
RDx:
RPx:
WRITE PINx
WRx:
ANALOG INPUT/OUTPUT PIN n ON PORTx
DIGITAL INPUT PIN n ON PORTx
RRx: READ PORTx REGISTER
WPx:
WRITE PORTx
AIOxn:
DIxn:
READ PORTx PIN
WDx:
READ DDRx
WRITE DDRxPUOVxn:
RDx
CLK
I/O
DIxn
AIOxn
CLK:
I/O
DIEOVxn
DIEOExn
PVOExn
DDOExn
PVOVxn
0
1
PUOExn
PUOVxn
0
1DDOVxn
SLEEP
PUD
WDx
D
QCLR
DDxn
Q
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Table 5-31 summarizes the function of the overriding signals. The pin and port indexes from Figure 5-26 on page 82 are not
shown in the succeeding tables. The overriding signals are generated internally in the modules having the alternate function.
The following subsections shortly describe the alternate functions for each port, and relate the overriding signals to the
alternate function. Refer to the alternate function description for further details.
5.10.3.1 MCU Control Register – MCUCR
• Bit 4 – PUD: Pull-up Disable
When this bit is written to one, the pull-ups in the I/O ports are disabled even if the DDxn and PORTxn registers are
configured to enable the pull-ups ({DDxn, PORTxn} = 0b01). See Section 5.10.2.1 “Configuring the Pin” on page 78 for more
details about this feature.
Table 5-31. Generic Description of Overriding Signals for Alternate Functions
Signal Name Full Name Description
PUOE Pull-up override enable
If this signal is set, the pull-up enable is controlled by the PUOV signal. If
this signal is cleared, the pull-up is enabled when {DDxn, PORTxn, PUD} =
0b010.
PUOV Pull-up override value If PUOE is set, the pull-up is enabled/disabled when PUOV is set/cleared,
regardless of the setting of the DDxn, PORTxn, and PUD register bits.
DDOE Data direction override
enable
If this signal is set, the output driver enable is controlled by the DDOV
signal. If this signal is cleared, the output driver is enabled by the DDxn
register bit.
DDOV Data direction override
value
If DDOE is set, the output driver is enabled/disabled when DDOV is
set/cleared, regardless of the setting of the DDxn register bit.
PVOE Port value override
enable
If this signal is set and the output driver is enabled, the port value is
controlled by the PVOV signal. If PVOE is cleared, and the output driver is
enabled, the port value is controlled by the PORTxn register bit.
PVOV Port value override value If PVOE is set, the port value is set to PVOV, regardless of the setting of the
PORTxn register bit.
PTOE Port toggle override
enable If PTOE is set, the PORTxn register bit is inverted.
DIEOE Digital input enable
override enable
If this bit is set, the digital input enable is controlled by the DIEOV signal. If
this signal is cleared, the digital input enable is determined by MCU state
(normal mode, sleep mode).
DIEOV Digital input enable
override value
If DIEOE is set, the digital Input is enabled/disabled when DIEOV is
set/cleared, regardless of the MCU state (normal mode, sleep mode).
DI Digital input
This is the digital input to alternate functions. In the figure, the signal is
connected to the output of the Schmitt trigger but before the synchronizer.
Unless the digital input is used as a clock source, the module with the
alternate function will use its own synchronizer.
AIO Analog input/output This is the analog input/output to/from alternate functions. The signal is
connected directly to the pad, and can be used bi-directionally.
Bit 7 6 5 4 3 2 1 0
–––PUD– – IVSEL IVCE MCUCR
Read/Write R R R R/W R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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5.10.3.2 Alternate Functions of Port B
The port B pins with alternate functions are shown in Table 5-32.
The alternate pin configuration is as follows:
• XTAL2/TOSC2/PCINT7 – Port B, Bit 7
XTAL2: Chip clock oscillator pin 2. Used as clock pin for crystal oscillator or low-frequency crystal oscillator. When used as a
clock pin, the pin can not be used as an I/O pin.
TOSC2: Timer oscillator pin 2. Used only if internal calibrated RC oscillator is selected as chip clock source, and the
asynchronous timer is enabled by the correct setting in ASSR. When the AS2 bit in ASSR is set (one) and the EXCLK bit is
cleared (zero) to enable asynchronous clocking of Timer/Counter2 using the crystal oscillator, pin PB7 is disconnected from
the port, and becomes the inverting output of the oscillator amplifier. In this mode, a crystal oscillator is connected to this pin,
and the pin cannot be used as an I/O pin.
PCINT7: Pin change interrupt source 7. The PB7 pin can serve as an external interrupt source.
If PB7 is used as a clock pin, DDB7, PORTB7 and PINB7 will all read 0.
• XTAL1/TOSC1/PCINT6 – Port B, Bit 6
XTAL1: Chip clock oscillator pin 1. Used for all chip clock sources except internal calibrated RC oscillator. When used as a
clock pin, the pin can not be used as an I/O pin.
TOSC1: Timer oscillator pin 1. Used only if internal calibrated RC oscillator is selected as chip clock source, and the
asynchronous timer is enabled by the correct setting in ASSR. When the AS2 bit in ASSR is set (one) to enable
asynchronous clocking of Timer/Counter2, pin PB6 is disconnected from the port, and becomes the input of the inverting
oscillator amplifier. In this mode, a crystal oscillator is connected to this pin, and the pin can not be used as an I/O pin.
PCINT6: Pin change interrupt source 6. The PB6 pin can serve as an external interrupt source.
If PB6 is used as a clock pin, DDB6, PORTB6 and PINB6 will all read 0.
Table 5-32. Port B Pins Alternate Functions
Port Pin Alternate Functions
PB7
XTAL2 (chip clock oscillator pin 2)
TOSC2 (timer oscillator pin 2)
PCINT7 (pin change interrupt 7)
PB6
XTAL1 (chip clock oscillator pin 1 or external clock input)
TOSC1 (timer oscillator pin 1)
PCINT6 (pin change interrupt 6)
PB5 SCK (SPI bus master clock input)
PCINT5 (pin change interrupt 5)
PB4 MISO (SPI bus master input/slave output)
PCINT4 (pin change interrupt 4)
PB3
MOSI (SPI bus master output/slave input)
OC2A (Timer/Counter2 output compare match A output)
PCINT3 (pin change interrupt 3)
PB2
SS (SPI bus master slave select)
OC1B (Timer/Counter1 output compare match B output)
PCINT2 (pin change interrupt 2)
PB1 OC1A (Timer/Counter1 output compare match A output)
PCINT1 (pin change interrupt 1)
PB0
ICP1 (Timer/Counter1 input capture input)
CLKO (divided system clock output)
PCINT0 (pin change interrupt 0)
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• SCK/PCINT5 – Port B, Bit 5
SCK: Master clock output, slave clock input pin for SPI channel. When the SPI is enabled as a slave, this pin is configured as
an input regardless of the setting of DDB5. When the SPI is enabled as a master, the data direction of this pin is controlled
by DDB5. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB5 bit.
PCINT5: Pin change interrupt source 5. The PB5 pin can serve as an external interrupt source.
• MISO/PCINT4 – Port B, Bit 4
MISO: Master data input, slave data output pin for SPI channel. When the SPI is enabled as a master, this pin is configured
as an input regardless of the setting of DDB4. When the SPI is enabled as a slave, the data direction of this pin is controlled
by DDB4. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB4 bit.
PCINT4: Pin change interrupt source 4. The PB4 pin can serve as an external interrupt source.
• MOSI/OC2/PCINT3 – Port B, Bit 3
MOSI: SPI Master data output, slave data input for SPI channel. When the SPI is enabled as a slave, this pin is configured
as an input regardless of the setting of DDB3. When the SPI is enabled as a master, the data direction of this pin is
controlled by DDB3. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB3 bit.
OC2, output compare match output: The PB3 pin can serve as an external output for the Timer/Counter2 compare match.
The PB3 pin has to be configured as an output (DDB3 set (one)) to serve this function. The OC2 pin is also the output pin for
the PWM mode timer function.
PCINT3: Pin change interrupt source 3. The PB3 pin can serve as an external interrupt source.
• SS/OC1B/PCINT2 – Port B, Bit 2
SS: Slave select input. When the SPI is enabled as a slave, this pin is configured as an input regardless of the setting of
DDB2. As a slave, the SPI is activated when this pin is driven low. When the SPI is enabled as a master, the data direction
of this pin is controlled by DDB2. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the
PORTB2 bit.
OC1B, output compare match output: The PB2 pin can serve as an external output for the Timer/Counter1 compare match
B. The PB2 pin has to be configured as an output (DDB2 set (one)) to serve this function. The OC1B pin is also the output
pin for the PWM mode timer function.
PCINT2: Pin change interrupt source 2. The PB2 pin can serve as an external interrupt source.
• OC1A/PCINT1 – Port B, Bit 1
OC1A, output compare match output: The PB1 pin can serve as an external output for the Timer/Counter1 compare match
A. The PB1 pin has to be configured as an output (DDB1 set (one)) to serve this function. The OC1A pin is also the output
pin for the PWM mode timer function.
PCINT1: Pin change interrupt source 1. The PB1 pin can serve as an external interrupt source.
• ICP1/CLKO/PCINT0 – Port B, Bit 0
ICP1, input capture pin: The PB0 pin can act as an input capture pin for Timer/Counter1.
CLKO, divided system clock: The divided system clock can be output on the PB0 pin. The divided system clock will be output
if the CKOUT fuse is programmed, regardless of the PORTB0 and DDB0 settings. It will also be output during reset.
PCINT0: pin change interrupt source 0. The PB0 pin can serve as an external interrupt source.
Table 5-33 on page 86 and Table 5-34 on page 86 relate the alternate functions of Port B to the overriding signals shown in
Figure 5-26 on page 82. SPI MSTR INPUT and SPI SLAVE OUTPUT constitute the MISO signal, while MOSI is divided into
SPI MSTR OUTPUT and SPI SLAVE INPUT.
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Table 5-33. Overriding Signals for Alternate Functions in PB7..PB4
Signal Name PB7/XTAL2/TOSC2/PCINT7(1) PB6/XTAL1/TOSC1/PCINT6(1) PB5/SCK/PCINT5 PB4/MISO/PCINT4
PUOE INTRC × EXTCK+ AS2 INTRC + AS2 SPE × MSTR SPE × MSTR
PUOV 00PORTB5 × PUD PORTB4 × PUD
DDOE INTRC × EXTCK+ AS2 INTRC + AS2 SPE × MSTR SPE × MSTR
DDOV 0 0 0 0
PVOE 00SPE × MSTR SPE × MSTR
PVOV 00SCK OUTPUT SPI SLAVE OUTPUT
DIEOE INTRC × EXTCK + AS2 +
PCINT7 × PCIE0
INTRC + AS2 + PCINT6 ×
PCIE0 PCINT5 × PCIE0 PCINT4 × PCIE0
DIEOV (INTRC + EXTCK) × AS2 INTRC × AS2 1 1
DI PCINT7 INPUT PCINT6 INPUT PCINT5 INPUT
SCK INPUT
PCINT4 INPUT
SPI MSTR INPUT
AIO Oscillator output Oscillator/clock input – –
Note: 1. INTRC means that one of the internal RC oscillators are selected (by the CKSEL fuses), EXTCK means that
external clock is selected (by the CKSEL fuses).
Table 5-34. Overriding Signals for Alternate Functions in PB3..PB0
Signal Name PB3/MOSI/OC2/PCINT3 PB2/SS/OC1B/PCINT2 PB1/OC1A/PCINT1 PB0/ICP1/PCINT0
PUOE SPE × MSTR SPE × MSTR 0 0
PUOV PORTB3 × PUD PORTB2 × PUD 0 0
DDOE SPE × MSTR SPE × MSTR 0 0
DDOV 0000
PVOE SPE × MSTR +
OC2A ENABLE OC1B ENABLE OC1A ENABLE 0
PVOV SPI MSTR OUTPUT +
OC2A OC1B OC1A 0
DIEOE PCINT3 × PCIE0 PCINT2 × PCIE0 PCINT1 × PCIE0 PCINT0 × PCIE0
DIEOV 1111
DI PCINT3 INPUT
SPI SLAVE INPUT
PCINT2 INPUT
SPI SS PCINT1 INPUT PCINT0 INPUT
ICP1 INPUT
AIO ––––
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5.10.3.3 Alternate Functions of Port C
The port C pins with alternate functions are shown in Table 5-35.
The alternate pin configuration is as follows:
• RESET/PCINT14 – Port C, Bit 6
RESET, reset pin: When the RSTDISBL fuse is programmed, this pin functions as a normal I/O pin, and the part will have to
rely on power-on reset and brown-out reset as its reset sources. When the RSTDISBL fuse is unprogrammed, the reset
circuitry is connected to the pin, and the pin can not be used as an I/O pin.
If PC6 is used as a reset pin, DDC6, PORTC6 and PINC6 will all read 0.
PCINT14: Pin change interrupt source 14. The PC6 pin can serve as an external interrupt source.
• SCL/ADC5/PCINT13 – Port C, Bit 5
SCL, 2-wire serial interface clock: When the TWEN bit in TWCR is set (one) to enable the 2-wire serial interface, pin PC5 is
disconnected from the port and becomes the serial clock I/O pin for the 2-wire serial interface. In this mode, there is a spike
filter on the pin to suppress spikes shorter than 50ns on the input signal, and the pin is driven by an open drain driver with
slew-rate limitation.
PC5 can also be used as ADC input channel 5. Note that ADC input channel 5 uses digital power.
PCINT13: Pin change interrupt source 13. The PC5 pin can serve as an external interrupt source.
• SDA/ADC4/PCINT12 – Port C, Bit 4
SDA, 2-wire serial interface data: When the TWEN bit in TWCR is set (one) to enable the 2-wire serial interface, pin PC4 is
disconnected from the port and becomes the serial data I/O pin for the 2-wire serial interface. In this mode, there is a spike
filter on the pin to suppress spikes shorter than 50ns on the input signal, and the pin is driven by an open drain driver with
slew-rate limitation.
PC4 can also be used as ADC input Channel 4. Note that ADC input channel 4 uses digital power.
PCINT12: Pin change interrupt source 12. The PC4 pin can serve as an external interrupt source.
• ADC3/PCINT11 – Port C, Bit 3
PC3 can also be used as ADC input Channel 3. Note that ADC input channel 3 uses analog power.
PCINT11: Pin change interrupt source 11. The PC3 pin can serve as an external interrupt source.
Table 5-35. Port C Pins Alternate Functions
Port Pin Alternate Function
PC6 RESET (reset pin)
PCINT14 (pin change interrupt 14)
PC5
ADC5 (ADC input channel 5)
SCL (2-wire serial bus clock line)
PCINT13 (pin change interrupt 13)
PC4
ADC4 (ADC input channel 4)
SDA (2-wire serial bus data input/output line)
PCINT12 (pin change interrupt 12)
PC3 ADC3 (ADC input channel 3)
PCINT11 (pin change interrupt 11)
PC2 ADC2 (ADC input channel 2)
PCINT10 (pin change interrupt 10)
PC1 ADC1 (ADC input channel 1)
PCINT9 (pin change interrupt 9)
PC0 ADC0 (ADC input channel 0)
PCINT8 (pin change interrupt 8)
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• ADC2/PCINT10 – Port C, Bit 2
PC2 can also be used as ADC input channel 2. Note that ADC input channel 2 uses analog power.
PCINT10: Pin change interrupt source 10. The PC2 pin can serve as an external interrupt source.
• ADC1/PCINT9 – Port C, Bit 1
PC1 can also be used as ADC input channel 1. Note that ADC input channel 1 uses analog power.
PCINT9: Pin change interrupt source 9. The PC1 pin can serve as an external interrupt source.
• ADC0/PCINT8 – Port C, Bit 0
PC0 can also be used as ADC input Channel 0. Note that ADC input channel 0 uses analog power.
PCINT8: Pin change interrupt source 8. The PC0 pin can serve as an external interrupt source.
Table 5-36 and Table 5-37 relate the alternate functions of port C to the overriding signals shown in Figure 5-26 on page 82.
Table 5-36. Overriding Signals for Alternate Functions in PC6..PC4(1)
Signal Name PC6/RESET/PCINT14 PC5/SCL/ADC5/PCINT13 PC4/SDA/ADC4/PCINT12
PUOE RSTDISBL TWEN TWEN
PUOV 1PORTC5 × PUD PORTC4 × PUD
DDOE RSTDISBL TWEN TWEN
DDOV 0SCL_OUT SDA_OUT
PVOE 0TWEN TWEN
PVOV 0 0 0
DIEOE RSTDISBL + PCINT14 × PCIE1 PCINT13 × PCIE1 + ADC5D PCINT12 × PCIE1 + ADC4D
DIEOV RSTDISBL PCINT13 × PCIE1 PCINT12 × PCIE1
DI PCINT14 INPUT PCINT13 INPUT PCINT12 INPUT
AIO RESET INPUT ADC5 INPUT / SCL INPUT ADC4 INPUT / SDA INPUT
Note: 1. When enabled, the 2-wire serial interface enables slew-rate controls on the output pins PC4 and PC5. This is
not shown in the figure. In addition, spike filters are connected between the AIO outputs shown in the port
figure and the digital logic of the TWI module.
Table 5-37. Overriding Signals for Alternate Functions in PC3..PC0
Signal Name PC3/ADC3/PCINT11 PC2/ADC2/PCINT10 PC1/ADC1/PCINT9 PC0/ADC0/PCINT8
PUOE 0 0 0 0
PUOV 0 0 0 0
DDOE 0 0 0 0
DDOV 0 0 0 0
PVOE 0 0 0 0
PVOV 0 0 0 0
DIEOE PCINT11 × PCIE1 +
ADC3D
PCINT10 × PCIE1 +
ADC2D
PCINT9 × PCIE1 +
ADC1D
PCINT8 × PCIE1 +
ADC0D
DIEOV PCINT11 × PCIE1 PCINT10 × PCIE1 PCINT9 × PCIE1 PCINT8 × PCIE1
DI PCINT11 INPUT PCINT10 INPUT PCINT9 INPUT PCINT8 INPUT
AIO ADC3 INPUT ADC2 INPUT ADC1 INPUT ADC0 INPUT
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5.10.3.4 Alternate Functions of Port D
The port D pins with alternate functions are shown in Table 5-38.
The alternate pin configuration is as follows:
• AIN1/OC2B/PCINT23 – Port D, Bit 7
AIN1, analog comparator negative input. Configure the port pin as input with the internal pull-up switched off to avoid the
digital port function from interfering with the function of the analog comparator.
PCINT23: Pin change interrupt source 23. The PD7 pin can serve as an external interrupt source.
• AIN0/OC0A/PCINT22 – Port D, Bit 6
AIN0, analog comparator positive Input. Configure the port pin as input with the internal pull-up switched off to avoid the
digital port function from interfering with the function of the analog comparator.
OC0A, output compare match output: The PD6 pin can serve as an external output for the Timer/Counter0 compare match
A. The PD6 pin has to be configured as an output (DDD6 set (one)) to serve this function. The OC0A pin is also the output
pin for the PWM mode timer function.
PCINT22: Pin change interrupt source 22. The PD6 pin can serve as an external interrupt source.
• T1/OC0B/PCINT21 – Port D, Bit 5
T1, Timer/Counter1 counter source.
OC0B, output compare match output: The PD5 pin can serve as an external output for the Timer/Counter0 compare match
B. The PD5 pin has to be configured as an output (DDD5 set (one)) to serve this function. The OC0B pin is also the output
pin for the PWM mode timer function.
PCINT21: Pin change interrupt source 21. The PD5 pin can serve as an external interrupt source.
Table 5-38. Port D Pins Alternate Functions
Port Pin Alternate Function
PD7 AIN1 (analog comparator negative input)
PCINT23 (pin change interrupt 23)
PD6
AIN0 (analog comparator positive input)
OC0A (Timer/Counter0 output compare match A output)
PCINT22 (pin change interrupt 22)
PD5
T1 (Timer/Counter 1 external counter input)
OC0B (Timer/Counter0 output compare match B output)
PCINT21 (pin change interrupt 21)
PD4
XCK (USART external clock input/output)
T0 (Timer/Counter 0 external counter input)
PCINT20 (pin change interrupt 20)
PD3
INT1 (external interrupt 1 input)
OC2B (Timer/Counter2 output compare match B output)
PCINT19 (pin change interrupt 19)
PD2 INT0 (external interrupt 0 input)
PCINT18 (pin change interrupt 18)
PD1 TXD (USART output pin)
PCINT17 (pin change interrupt 17)
PD0 RXD (USART input pin)
PCINT16 (pin change interrupt 16)
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• XCK/T0/PCINT20 – Port D, Bit 4
XCK, USART external clock.
T0, Timer/Counter0 counter source.
PCINT20: Pin change interrupt source 20. The PD4 pin can serve as an external interrupt source.
• INT1/OC2B/PCINT19 – Port D, Bit 3
INT1, external interrupt source 1: The PD3 pin can serve as an external interrupt source.
OC2B, output compare match output: The PD3 pin can serve as an external output for the Timer/Counter0 compare match
B. The PD3 pin has to be configured as an output (DDD3 set (one)) to serve this function. The OC2B pin is also the output
pin for the PWM mode timer function.
PCINT19: Pin change interrupt source 19. The PD3 pin can serve as an external interrupt source.
• INT0/PCINT18 – Port D, Bit 2
INT0, external interrupt source 0: The PD2 pin can serve as an external interrupt source.
PCINT18: Pin change interrupt source 18. The PD2 pin can serve as an external interrupt source.
• TXD/PCINT17 – Port D, Bit 1
TXD, transmit data (Data output pin for the USART). When the USART Transmitter is enabled, this pin is configured as an
output regardless of the value of DDD1.
PCINT17: Pin change interrupt source 17. The PD1 pin can serve as an external interrupt source.
• RXD/PCINT16 – Port D, Bit 0
RXD, receive data (Data input pin for the USART). When the USART receiver is enabled this pin is configured as an input
regardless of the value of DDD0. When the USART forces this pin to be an input, the pull-up can still be controlled by the
PORTD0 bit.
PCINT16: Pin change interrupt source 16. The PD0 pin can serve as an external interrupt source.
Table 5-39 and Table 5-40 on page 91 relate the alternate functions of Port D to the overriding signals shown in
Figure 5-26 on page 82.
Table 5-39. Overriding Signals for Alternate Functions PD7..PD4
Signal Name PD7/AIN1/PCINT23 PD6/AIN0/OC0A/PCINT22 PD5/T1/OC0B/PCINT21 PD4/XCK/T0/PCINT20
PUOE 0 0 0 0
PUO 0 0 0 0
DDOE 0 0 0 0
DDOV 0 0 0 0
PVOE 0OC0A ENABLE OC0B ENABLE UMSEL
PVOV 0OC0A OC0B XCK OUTPUT
DIEOE PCINT23 × PCIE2 PCINT22 × PCIE2 PCINT21 × PCIE2 PCINT20 × PCIE2
DIEOV 1 1 1 1
DI PCINT23 INPUT PCINT22 INPUT PCINT21 INPUT
T1 INPUT
PCINT20 INPUT
XCK INPUT
T0 INPUT
AIO AIN1 INPUT AIN0 INPUT – –
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5.10.4 Register Description for I/O Ports
5.10.4.1 The Port B Data Register – PORTB
5.10.4.2 The Port B Data Direction Register – DDRB
5.10.4.3 The Port B Input Pins Address – PINB
5.10.4.4 The Port C Data Register – PORTC
5.10.4.5 The Port C Data Direction Register – DDRC
Table 5-40. Overriding Signals for Alternate Functions in PD3..PD0
Signal Name PD3/OC2B/INT1/PCINT19 PD2/INT0/PCINT18 PD1/TXD/PCINT17 PD0/RXD/PCINT16
PUOE 0 0 TXEN RXEN
PUO 0 0 0 PORTD0 × PUD
DDOE 0 0 TXEN RXEN
DDOV 0 0 1 0
PVOE OC2B ENABLE 0TXEN 0
PVOV OC2B 0TXD 0
DIEOE INT1 ENABLE + PCINT19
× PCIE2
INT0 ENABLE + PCINT18
× PCIE1 PCINT17 × PCIE2 PCINT16 × PCIE2
DIEOV 1 1 1 1
DI PCINT19 INPUT
INT1 INPUT
PCINT18 INPUT
INT0 INPUT PCINT17 INPUT PCINT16 INPUT
RXD
AIO – – – –
Bit 76543210
PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 PORTB
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
DDB7 DDB6 DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 DDRB
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 PINB
Read/Write R R R RRRRR
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A
Bit 76543210
– PORTC6 PORTC5 PORTC4 PORTC3 PORTC2 PORTC1 PORTC0 PORTC
Read/Write R R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
– DDC6 DDC5 DDC4 DDC3 DDC2 DDC1 DDC0 DDRC
Read/Write R R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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5.10.4.6 The Port C Input Pins Address – PINC
5.10.4.7 The Port D Data Register – PORTD
5.10.4.8 The Port D Data Direction Register – DDRD
5.10.4.9 The Port D Input Pins Address – PIND
5.11 External Interrupts
The external interrupts are triggered by the INT0 and INT1 pins or any of the PCINT23..0 pins. Observe that, if enabled, the
interrupts will trigger even if the INT0 and INT1 or PCINT23..0 pins are configured as outputs. This feature provides a way of
generating a software interrupt. The pin change interrupt PCI2 will trigger if any enabled PCINT23..16 pin toggles. The pin
change interrupt PCI1 will trigger if any enabled PCINT14..8 pin toggles. The pin change interrupt PCI0 will trigger if any
enabled PCINT7..0 pin toggles. The PCMSK2, PCMSK1 and PCMSK0 registers control which pins contribute to the pin
change interrupts. Pin change interrupts on PCINT23..0 are detected asynchronously. This implies that these interrupts can
be used for waking the part also from sleep modes other than idle mode.
The INT0 and INT1 interrupts can be triggered by a falling or rising edge or a low level. This is set up as indicated in the
specification for the external interrupt control register A – EICRA. When the INT0 or INT1 interrupts are enabled and are
configured as level triggered, the interrupts will trigger as long as the pin is held low. Note that recognition of falling or rising
edge interrupts on INT0 or INT1 requires the presence of an I/O clock, described in Section 5.6.1 “Clock Systems and their
Distribution” on page 46. Low level interrupt on INT0 and INT1 is detected asynchronously. This implies that this interrupt
can be used for waking the part also from sleep modes other than idle mode. The I/O clock is halted in all sleep modes
except idle mode.
Note that if a level triggered interrupt is used for wake-up from power-down, the required level must be held long enough for
the MCU to complete the wake-up to trigger the level interrupt. If the level disappears before the end of the start-up time, the
MCU will still wake up, but no interrupt will be generated. The start-up time is defined by the SUT and CKSEL fuses as
described in Section 5.6 “System Clock and Clock Options” on page 46.
Bit 76543210
– PINC6 PINC5 PINC4 PINC3 PINC2 PINC1 PINC0 PINC
Read/Write RRRRRRRR
Initial Value 0 N/A N/A N/A N/A N/A N/A N/A
Bit 76543210
PORTD7 PORTD6 PORTD5 PORTD4 PORTD3 PORTD2 PORTD1 PORTD0 PORTD
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
DDD7 DDD6 DDD5 DDD4 DDD3 DDD2 DDD1 DDD0 DDRD
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
PIND7 PIND6 PIND5 PIND4 PIND3 PIND2 PIND1 PIND0 PIND
Read/Write R R R R R R R R
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A
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5.11.1 External Interrupt Control Register A – EICRA
The external interrupt control register A contains control bits for interrupt sense control.
• Bit 7..4 – Res: Reserved Bits
These bits are unused bits in the Atmel® ATA6612C/ATA6613C, and will always read as zero.
• Bit 3, 2 – ISC11, ISC10: Interrupt Sense Control 1 Bit 1 and Bit 0
The external interrupt 1 is activated by the external pin INT1 if the SREG I-flag and the corresponding interrupt mask are set.
The level and edges on the external INT1 pin that activate the interrupt are defined in Table 5-41. The value on the INT1 pin
is sampled before detecting edges. If edge or toggle interrupt is selected, pulses that last longer than one clock period will
generate an interrupt. Shorter pulses are not guaranteed to generate an interrupt. If low level interrupt is selected, the low
level must be held until the completion of the currently executing instruction to generate an interrupt.
• Bit 1, 0 – ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0
The external interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the corresponding interrupt mask are set.
The level and edges on the external INT0 pin that activate the interrupt are defined in Table 5-42. The value on the INT0 pin
is sampled before detecting edges. If edge or toggle interrupt is selected, pulses that last longer than one clock period will
generate an interrupt. Shorter pulses are not guaranteed to generate an interrupt. If low level interrupt is selected, the low
level must be held until the completion of the currently executing instruction to generate an interrupt.
Bit 76543210
––––ISC11ISC10ISC01ISC00EICRA
Read/Write RRRRR/WR/WR/WR/W
Initial Value00000000
Table 5-41. Interrupt 1 Sense Control
ISC11 ISC10 Description
0 0 The low level of INT1 generates an interrupt request.
0 1 Any logical change on INT1 generates an interrupt request.
1 0 The falling edge of INT1 generates an interrupt request.
1 1 The rising edge of INT1 generates an interrupt request.
Table 5-42. Interrupt 0 Sense Control
ISC01 ISC00 Description
0 0 The low level of INT0 generates an interrupt request.
0 1 Any logical change on INT0 generates an interrupt request.
1 0 The falling edge of INT0 generates an interrupt request.
1 1 The rising edge of INT0 generates an interrupt request.
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5.11.2 External Interrupt Mask Register – EIMSK
• Bit 7..2 – Res: Reserved Bits
These bits are unused bits in the Atmel® ATA6612C/ATA6613C, and will always read as zero.
• Bit 1 – INT1: External Interrupt Request 1 Enable
When the INT1 bit is set (one) and the I-bit in the status register (SREG) is set (one), the external pin interrupt is enabled.
The interrupt sense control1 bits 1/0 (ISC11 and ISC10) in the external interrupt control register A (EICRA) define whether
the external interrupt is activated on rising and/or falling edge of the INT1 pin or level sensed. Activity on the pin will cause an
interrupt request even if INT1 is configured as an output. The corresponding interrupt of external interrupt request 1 is
executed from the INT1 interrupt vector.
• Bit 0 – INT0: External Interrupt Request 0 Enable
When the INT0 bit is set (one) and the I-bit in the status register (SREG) is set (one), the external pin interrupt is enabled.
The interrupt sense control0 bits 1/0 (ISC01 and ISC00) in the external interrupt control register A (EICRA) define whether
the external interrupt is activated on rising and/or falling edge of the INT0 pin or level sensed. Activity on the pin will cause an
interrupt request even if INT0 is configured as an output. The corresponding interrupt of external interrupt request 0 is
executed from the INT0 interrupt vector.
5.11.3 External Interrupt Flag Register – EIFR
• Bit 7..2 – Res: Reserved Bits
These bits are unused bits in the Atmel ATA6612C/ATA6613C, and will always read as zero.
• Bit 1 – INTF1: External Interrupt Flag 1
When an edge or logic change on the INT1 pin triggers an interrupt request, INTF1 becomes set (one). If the I-bit in SREG
and the INT1 bit in EIMSK are set (one), the MCU will jump to the corresponding interrupt vector. The flag is cleared when
the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it. This flag is always cleared
when INT1 is configured as a level interrupt.
• Bit 0 – INTF0: External Interrupt Flag 0
When an edge or logic change on the INT0 pin triggers an interrupt request, INTF0 becomes set (one). If the I-bit in SREG
and the INT0 bit in EIMSK are set (one), the MCU will jump to the corresponding interrupt vector. The flag is cleared when
the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it. This flag is always cleared
when INT0 is configured as a level interrupt.
Bit 76543210
––––––INT1INT0EIMSK
Read/Write R R R R R R R/W R/W
Initial Value00000000
Bit 76543210
––––––INTF1INTF0EIFR
Read/Write R R R R R R R/W R/W
Initial Value00000000
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5.11.4 Pin Change Interrupt Control Register - PCICR
• Bit 7..3 - Res: Reserved Bits
These bits are unused bits in the Atmel® ATA6612C/ATA6613C, and will always read as zero.
• Bit 2 - PCIE2: Pin Change Interrupt Enable 2
When the PCIE2 bit is set (one) and the I-bit in the status register (SREG) is set (one), pin change interrupt 2 is enabled. Any
change on any enabled PCINT23..16 pin will cause an interrupt. The corresponding interrupt of pin change interrupt request
is executed from the PCI2 interrupt vector. PCINT23..16 pins are enabled individually by the PCMSK2 register.
• Bit 1 - PCIE1: Pin Change Interrupt Enable 1
When the PCIE1 bit is set (one) and the I-bit in the status register (SREG) is set (one), pin change interrupt 1 is enabled. Any
change on any enabled PCINT14..8 pin will cause an interrupt. The corresponding interrupt of pin change interrupt request is
executed from the PCI1 interrupt vector. PCINT14..8 pins are enabled individually by the PCMSK1 register.
• Bit 0 - PCIE0: Pin Change Interrupt Enable 0
When the PCIE0 bit is set (one) and the I-bit in the status register (SREG) is set (one), pin change interrupt 0 is enabled. Any
change on any enabled PCINT7..0 pin will cause an interrupt. The corresponding interrupt of pin change interrupt request is
executed from the PCI0 interrupt vector. PCINT7..0 pins are enabled individually by the PCMSK0 register.
5.11.5 Pin Change Interrupt Flag Register - PCIFR
• Bit 7..3 - Res: Reserved Bits
These bits are unused bits in the Atmel ATA6612C/ATA6613C, and will always read as zero.
• Bit 2 - PCIF2: Pin Change Interrupt Flag 2
When a logic change on any PCINT23..16 pin triggers an interrupt request, PCIF2 becomes set (one). If the I-bit in SREG
and the PCIE2 bit in PCICR are set (one), the MCU will jump to the corresponding interrupt vector. The flag is cleared when
the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it.
• Bit 1 - PCIF1: Pin Change Interrupt Flag 1
When a logic change on any PCINT14..8 pin triggers an interrupt request, PCIF1 becomes set (one). If the I-bit in SREG and
the PCIE1 bit in PCICR are set (one), the MCU will jump to the corresponding interrupt vector. The flag is cleared when the
interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it.
• Bit 0 - PCIF0: Pin Change Interrupt Flag 0
When a logic change on any PCINT7..0 pin triggers an interrupt request, PCIF0 becomes set (one). If the I-bit in SREG and
the PCIE0 bit in PCICR are set (one), the MCU will jump to the corresponding interrupt vector. The flag is cleared when the
interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it.
Bit 76543210
– – – – – PCIE2 PCIE1 PCIE0 PCICR
Read/Write R R R R R R/W R/W R/W
Initial Value00000000
Bit 76543210
–––––PCIF2PCIF1PCIF0PCIFR
Read/Write R R R R R R/W R/W R/W
Initial Value00000000
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5.11.6 Pin Change Mask Register 2 – PCMSK2
• Bit 7..0 – PCINT23..16: Pin Change Enable Mask 23..16
Each PCINT23..16-bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT23..16 is set
and the PCIE2 bit in PCICR is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT23..16 is cleared,
pin change interrupt on the corresponding I/O pin is disabled.
5.11.7 Pin Change Mask Register 1 – PCMSK1
• Bit 7 – Res: Reserved Bit
This bit is an unused bit in the Atmel® ATA6612C/ATA6613C, and will always read as zero.
• Bit 6..0 – PCINT14..8: Pin Change Enable Mask 14..8
Each PCINT14..8-bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT14..8 is set and
the PCIE1 bit in PCICR is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT14..8 is cleared, pin
change interrupt on the corresponding I/O pin is disabled.
5.11.8 Pin Change Mask Register 0 – PCMSK0
• Bit 7..0 – PCINT7..0: Pin Change Enable Mask 7..0
Each PCINT7..0 bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT7..0 is set and the
PCIE0 bit in PCICR is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT7..0 is cleared, pin change
interrupt on the corresponding I/O pin is disabled.
5.12 8-bit Timer/Counter0 with PWM
Timer/Counter0 is a general purpose 8-bit Timer/Counter module, with two independent output compare Units, and with
PWM support. It allows accurate program execution timing (event management) and wave generation. The main features
are:
●Two independent output compare units
●Double buffered output compare registers
●Clear timer on compare match (auto reload)
●Glitch free, phase correct pulse width modulator (PWM)
●Variable PWM period
●Frequency generator
●Three independent interrupt sources (TOV0, OCF0A, and OCF0B)
Bit 76543210
PCINT23 PCINT22 PCINT21 PCINT20 PCINT19 PCINT18 PCINT17 PCINT16 PCMSK2
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
– PCINT14 PCINT13 PCINT12 PCINT11 PCINT10 PCINT9 PCINT8 PCMSK1
Read/Write R R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
PCINT7 PCINT6 PCINT5 PCINT4 PCINT3 PCINT2 PCINT1 PCINT0 PCMSK0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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5.12.1 Overview
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 5-27. The device-specific I/O register and bit
locations are listed in the Section 5.12.8 “8-bit Timer/Counter Register Description” on page 107.
The PRTIM0 bit in Section 5.7.7.1 “Power Reduction Register - PRR” on page 58 must be written to zero to enable
Timer/Counter0 module.
Figure 5-27. 8-bit Timer/Counter Block Diagram
TCNTn
Timer/Counter
Count
Clear
Direction
OCRnA
OCRnB
TCCRnA TCCRnB
=
TOP BOTTOM
OCnA (Int. Req.)
Waveform
Generation
Fixed
TOP
Value
DATA BUS
=
==
0
OCnA
OCnB (Int. Req.)
Waveform
Generation OCnB
Control Logic clkTn
clkI/O
Prescaler
TOVn (Int. Req.)
T/C
Oscillator
TOSC1
TOSC2
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5.12.1.1 Definitions
Many register and bit references in this section are written in general form. A lower case “n” replaces the Timer/Counter
number, in this case 0. A lower case “x” replaces the output compare unit, in this case compare unit A or compare unit B.
However, when using the register or bit defines in a program, the precise form must be used, i.e., TCNT0 for accessing
Timer/Counter0 counter value and so on.
The definitions in Table 5-43 are also used extensively throughout the document.
5.12.1.2 Registers
The Timer/Counter (TCNT0) and output compare registers (OCR0A and OCR0B) are 8-bit registers. Interrupt request
(abbreviated to Int.Req. in the figure) signals are all visible in the timer interrupt flag register (TIFR0). All interrupts are
individually masked with the timer interrupt mask register (TIMSK0). TIFR0 and TIMSK0 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on the T0 pin. The clock select
logic block controls which clock source and edge the Timer/Counter uses to increment (or decrement) its value. The
Timer/Counter is inactive when no clock source is selected. The output from the clock select logic is referred to as the timer
clock (clkT0).
The double buffered output compare registers (OCR0A and OCR0B) are compared with the Timer/Counter value at all
times. The result of the compare can be used by the waveform generator to generate a PWM or variable frequency output on
the output compare pins (OC0A and OC0B). See Section 5.14.6.3 “Using the Output Compare Unit” on page 123 for details.
The compare match event will also set the compare flag (OCF0A or OCF0B) which can be used to generate an output
compare interrupt request.
5.12.2 Timer/Counter Clock Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock source is selected by the clock
select logic which is controlled by the clock select (CS02:0) bits located in the Timer/Counter control register (TCCR0B). For
details on clock sources and prescaler (see Section 5.13 “Timer/Counter0 and Timer/Counter1 Prescalers” on page 112).
5.12.3 Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure 5-28 shows a block diagram
of the counter and its surroundings.
Figure 5-28. Counter Unit Block Diagram
Table 5-43. General Counter Definitions
Parameter Definition
BOTTOM The counter reaches the BOTTOM when it becomes 0x00.
MAX The counter reaches its MAXimum when it becomes 0xFF (decimal 255).
TOP
The counter reaches the TOP when it becomes equal to the highest value in the count sequence. The
TOP value can be assigned to be the fixed value 0xFF (MAX) or the value stored in the OCR0A register.
The assignment is dependent on the mode of operation.
TopBottom
TOVn
(Int. Req.)
DATA BUS
Control Logic
TCNTn
clkTn
Count
Clear
Direction
Edge
Detector
(From Prescaler)
Clock Select
Tn
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Signal description (internal signals):
count Increment or decrement TCNT0 by 1.
direction Select between increment and decrement.
clear Clear TCNT0 (set all bits to zero).
clkTnTimer/Counter clock, referred to as clkT0 in the following.
top Signalize that TCNT0 has reached maximum value.
bottom Signalize that TCNT0 has reached minimum value (zero).
Depending of the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clkT0).
clkT0 can be generated from an external or internal clock source, selected by the clock select bits (CS02:0). When no clock
source is selected (CS02:0 = 0) the timer is stopped. However, the TCNT0 value can be accessed by the CPU, regardless of
whether clkT0 is present or not. A CPU write overrides (has priority over) all counter clear or count operations.
The counting sequence is determined by the setting of the WGM01 and WGM00 bits located in the Timer/Counter control
register (TCCR0A) and the WGM02 bit located in the Timer/Counter control register B (TCCR0B). There are close
connections between how the counter behaves (counts) and how waveforms are generated on the output compare outputs
OC0A and OC0B. For more details about advanced counting sequences and waveform generation (see Section 5.12.6
“Modes of Operation” on page 101).
The Timer/Counter overflow flag (TOV0) is set according to the mode of operation selected by the WGM02:0 bits. TOV0 can
be used for generating a CPU interrupt.
5.12.4 Output Compare Unit
The 8-bit comparator continuously compares TCNT0 with the output compare registers (OCR0A and OCR0B). Whenever
TCNT0 equals OCR0A or OCR0B, the comparator signals a match. A match will set the output compare flag (OCF0A or
OCF0B) at the next timer clock cycle. If the corresponding interrupt is enabled, the output compare flag generates an output
compare interrupt. The output compare flag is automatically cleared when the interrupt is executed. Alternatively, the flag
can be cleared by software by writing a logical one to its I/O bit location. The waveform generator uses the match signal to
generate an output according to operating mode set by the WGM02:0 bits and compare output mode (COM0x1:0) bits. The
max and bottom signals are used by the waveform generator for handling the special cases of the extreme values in some
modes of operation (see Section 5.12.6 “Modes of Operation” on page 101).
Figure 5-29 shows a block diagram of the output compare unit.
Figure 5-29. Output Compare Unit, Block Diagram
OCFnx (Int. Req.)
= (8-bit Comparator)
OCRnx
Waveform Generator
TCNTn
OCnx
Top
Bottom
FOCn
WGMn1:0 COMnX1:0
DATA BUS
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The OCR0x registers are double buffered when using any of the pulse width modulation (PWM) modes. For the normal and
clear timer on compare (CTC) modes of operation, the double buffering is disabled. The double buffering synchronizes the
update of the OCR0x compare registers to either top or bottom of the counting sequence. The synchronization prevents the
occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
The OCR0x register access may seem complex, but this is not case. When the double buffering is enabled, the CPU has
access to the OCR0x buffer register, and if double buffering is disabled the CPU will access the OCR0x directly.
5.12.4.1 Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced by writing a one to the force
output compare (FOC0x) bit. Forcing compare match will not set the OCF0x flag or reload/clear the timer, but the OC0x pin
will be updated as if a real compare match had occurred (the COM0x1:0 bits settings define whether the OC0x pin is set,
cleared or toggled).
5.12.4.2 Compare Match Blocking by TCNT0 Write
All CPU write operations to the TCNT0 register will block any compare match that occur in the next timer clock cycle, even
when the timer is stopped. This feature allows OCR0x to be initialized to the same value as TCNT0 without triggering an
interrupt when the Timer/Counter clock is enabled.
5.12.4.3 Using the Output Compare Unit
Since writing TCNT0 in any mode of operation will block all compare matches for one timer clock cycle, there are risks
involved when changing TCNT0 when using the output compare Unit, independently of whether the Timer/Counter is
running or not. If the value written to TCNT0 equals the OCR0x value, the compare match will be missed, resulting in
incorrect waveform generation. Similarly, do not write the TCNT0 value equal to BOTTOM when the counter is
downcounting.
The setup of the OC0x should be performed before setting the data direction register for the port pin to output. The easiest
way of setting the OC0x value is to use the force output compare (FOC0x) strobe bits in normal mode. The OC0x registers
keep their values even when changing between waveform generation modes.
Be aware that the COM0x1:0 bits are not double buffered together with the compare value. Changing the COM0x1:0 bits will
take effect immediately.
5.12.5 Compare Match Output Unit
The compare output mode (COM0x1:0) bits have two functions. The waveform generator uses the COM0x1:0 bits for
defining the output compare (OC0x) state at the next compare match. Also, the COM0x1:0 bits control the OC0x pin output
source. Figure 5-30 on page 101 shows a simplified schematic of the logic affected by the COM0x1:0 bit setting. The I/O
registers, I/O bits, and I/O pins in the figure are shown in bold. Only the parts of the general I/O port control registers (DDR
and PORT) that are affected by the COM0x1:0 bits are shown. When referring to the OC0x state, the reference is for the
internal OC0x register, not the OC0x pin. If a system reset occur, the OC0x register is reset to “0”.
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Figure 5-30. Compare Match Output Unit, Schematic
The general I/O port function is overridden by the output compare (OC0x) from the waveform generator if either of the
COM0x1:0 bits are set. However, the OC0x pin direction (input or output) is still controlled by the data direction register
(DDR) for the port pin. The data direction register bit for the OC0x pin (DDR_OC0x) must be set as output before the OC0x
value is visible on the pin. The port override function is independent of the waveform generation mode.
The design of the output compare pin logic allows initialization of the OC0x state before the output is enabled. Note that
some COM0x1:0 bit settings are reserved for certain modes of operation (see Section 5.12.8 “8-bit Timer/Counter Register
Description” on page 107).
5.12.5.1 Compare Output Mode and Waveform Generation
The waveform generator uses the COM0x1:0 bits differently in normal, CTC, and PWM modes. For all modes, setting the
COM0x1:0 = 0 tells the waveform generator that no action on the OC0x register is to be performed on the next compare
match. For compare output actions in the non-PWM modes refer to Table 5-44 on page 107. For fast PWM mode, refer to
Table 5-45 on page 107, and for phase correct PWM refer to Table 5-46 on page 107.
A change of the COM0x1:0 bits state will have effect at the first compare match after the bits are written. For non-PWM
modes, the action can be forced to have immediate effect by using the FOC0x strobe bits.
5.12.6 Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the output compare pins, is defined by the combination of
the waveform generation mode (WGM02:0) and compare output mode (COM0x1:0) bits. The compare output mode bits do
not affect the counting sequence, while the waveform generation mode bits do. The COM0x1:0 bits control whether the
PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes the COM0x1:0 bits
control whether the output should be set, cleared, or toggled at a compare match (see Section 5.12.5 “Compare Match
Output Unit” on page 100).
For detailed timing information refer to Section 5.12.7 “Timer/Counter Timing Diagrams” on page 105.
DATA BUS
0
1
QD
COMnx1
COMnx0
FOCnx
OCnx
Waveform
Generator
QD
PORT
QD
DDR
OCnx
Pin
clk
I/O
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5.12.6.1 Normal Mode
The simplest mode of operation is the normal mode (WGM02:0 = 0). In this mode the counting direction is always up
(incrementing), and no counter clear is performed. The counter simply overruns when it passes its maximum 8-bit value
(TOP = 0xFF) and then restarts from the bottom (0x00). In normal operation the Timer/Counter overflow flag (TOV0) will be
set in the same timer clock cycle as the TCNT0 becomes zero. The TOV0 flag in this case behaves like a ninth bit, except
that it is only set, not cleared. However, combined with the timer overflow interrupt that automatically clears the TOV0 flag,
the timer resolution can be increased by software. There are no special cases to consider in the normal mode, a new counter
value can be written anytime.
The output compare unit can be used to generate interrupts at some given time. Using the output compare to generate
waveforms in normal mode is not recommended, since this will occupy too much of the CPU time.
5.12.6.2 Clear Timer on Compare Match (CTC) Mode
In clear timer on compare or CTC mode (WGM02:0 = 2), the OCR0A register is used to manipulate the counter resolution. In
CTC mode the counter is cleared to zero when the counter value (TCNT0) matches the OCR0A. The OCR0A defines the top
value for the counter, hence also its resolution. This mode allows greater control of the compare match output frequency. It
also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 5-31. The counter value (TCNT0) increases until a compare match
occurs between TCNT0 and OCR0A, and then counter (TCNT0) is cleared.
Figure 5-31. CTC Mode, Timing Diagram
An interrupt can be generated each time the counter value reaches the TOP value by using the OCF0A Flag. If the interrupt
is enabled, the interrupt handler routine can be used for updating the TOP value. However, changing TOP to a value close to
BOTTOM when the counter is running with none or a low prescaler value must be done with care since the CTC mode does
not have the double buffering feature. If the new value written to OCR0A is lower than the current value of TCNT0, the
counter will miss the compare match. The counter will then have to count to its maximum value (0xFF) and wrap around
starting at 0x00 before the compare match can occur.
For generating a waveform output in CTC mode, the OC0A output can be set to toggle its logical level on each compare
match by setting the compare output mode bits to toggle mode (COM0A1:0 = 1). The OC0A value will not be visible on the
port pin unless the data direction for the pin is set to output. The waveform generated will have a maximum frequency of
fOC0 = fclk_I/O/2 when OCR0A is set to zero (0x00). The waveform frequency is defined by the following equation:
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
As for the normal mode of operation, the TOV0 flag is set in the same timer clock cycle that the counter counts from
MAX to 0x00.
12
TCNTn
(COMnx1:0 = 1)
OCn
(Toggle)
Period 3
OCnx Interrupt
Flag Set
4
fOCnx
fclk_I/O
2 N 1 OCRnx+()××
----------------------------------------------------
=
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5.12.6.3 Fast PWM Mode
The fast pulse width modulation or fast PWM mode (WGM02:0 = 3 or 7) provides a high frequency PWM waveform
generation option. The fast PWM differs from the other PWM option by its single-slope operation. The counter counts from
BOTTOM to TOP then restarts from BOTTOM. TOP is defined as 0xFF when WGM2:0 = 3, and OCR0A when WGM2:0 = 7.
In non-inverting compare output mode, the output compare (OC0x) is cleared on the compare match between TCNT0 and
OCR0x, and set at BOTTOM. In inverting compare output mode, the output is set on compare match and cleared at
BOTTOM. Due to the single-slope operation, the operating frequency of the fast PWM mode can be twice as high as the
phase correct PWM mode that use dual-slope operation. This high frequency makes the fast PWM mode well suited for
power regulation, rectification, and DAC applications. High frequency allows physically small sized external components
(coils, capacitors), and therefore reduces total system cost.
In fast PWM mode, the counter is incremented until the counter value matches the TOP value. The counter is then cleared at
the following timer clock cycle. The timing diagram for the fast PWM mode is shown in Figure 5-32. The TCNT0 value is in
the timing diagram shown as a histogram for illustrating the single-slope operation. The diagram includes non-inverted and
inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent compare matches between OCR0x
and TCNT0.
Figure 5-32. Fast PWM Mode, Timing Diagram
The Timer/Counter overflow flag (TOV0) is set each time the counter reaches TOP. If the interrupt is enabled, the interrupt
handler routine can be used for updating the compare value.
In fast PWM mode, the compare unit allows generation of PWM waveforms on the OC0x pins. Setting the COM0x1:0 bits to
two will produce a non-inverted PWM and an inverted PWM output can be generated by setting the COM0x1:0 to three:
Setting the COM0A1:0 bits to one allows the OC0A pin to toggle on compare matches if the WGM02 bit is set. This option is
not available for the OC0B pin (see Table 5-48 on page 108). The actual OC0x value will only be visible on the port pin if the
data direction for the port pin is set as output. The PWM waveform is generated by setting (or clearing) the OC0x register at
the compare match between OCR0x and TCNT0, and clearing (or setting) the OC0x register at the timer clock cycle the
counter is cleared (changes from TOP to BOTTOM).
1234567
TCNTn
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCn
OCn
Period
OCRnx Update and
TOVn Interrupt Flag Set
OCRnx Interrupt
Flag Set
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The PWM frequency for the output can be calculated by the following equation:
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A register represents special cases when generating a PWM waveform output in the fast
PWM mode. If the OCR0A is set equal to BOTTOM, the output will be a narrow spike for each MAX+1 timer clock cycle.
Setting the OCR0A equal to MAX will result in a constantly high or low output (depending on the polarity of the output set by
the COM0A1:0 bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OC0x to toggle its logical
level on each compare match (COM0x1:0 = 1). The waveform generated will have a maximum frequency of fOC0 = fclk_I/O/2
when OCR0A is set to zero. This feature is similar to the OC0A toggle in CTC mode, except the double buffer feature of the
output compare unit is enabled in the fast PWM mode.
5.12.6.4 Phase Correct PWM Mode
The phase correct PWM mode (WGM02:0 = 1 or 5) provides a high resolution phase correct PWM waveform generation
option. The phase correct PWM mode is based on a dual-slope operation. The counter counts repeatedly from BOTTOM to
TOP and then from TOP to BOTTOM. TOP is defined as 0xFF when WGM2:0 = 1, and OCR0A when WGM2:0 = 5.
In non-inverting compare output mode, the output compare (OC0x) is cleared on the compare match between TCNT0 and
OCR0x while upcounting, and set on the compare match while downcounting. In inverting output compare mode, the
operation is inverted. The dual-slope operation has lower maximum operation frequency than single slope operation.
However, due to the symmetric feature of the dual-slope PWM modes, these modes are preferred for motor control
applications.
In phase correct PWM mode the counter is incremented until the counter value matches TOP. When the counter reaches
TOP, it changes the count direction. The TCNT0 value will be equal to TOP for one timer clock cycle. The timing diagram for
the phase correct PWM mode is shown on Figure 5-33 on page 104. The TCNT0 value is in the timing diagram shown as a
histogram for illustrating the dual-slope operation. The diagram includes non-inverted and inverted PWM outputs. The small
horizontal line marks on the TCNT0 slopes represent compare matches between OCR0x and TCNT0.
Figure 5-33. Phase Correct PWM Mode, Timing Diagram
fOCnxPWM
fclk_I/O
N 256×
-------------------
=
123
TCNTn
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCn
OCn
Period
TOVn Interrupt
Flag Set
OCRnx Update
OCnx Interrupt
Flag Set
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The Timer/Counter overflow flag (TOV0) is set each time the counter reaches BOTTOM. The interrupt flag can be used to
generate an interrupt each time the counter reaches the BOTTOM value.
In phase correct PWM mode, the compare unit allows generation of PWM waveforms on the OC0x pins. Setting the
COM0x1:0 bits to two will produce a non-inverted PWM. An inverted PWM output can be generated by setting the
COM0x1:0 to three: Setting the COM0A0 bits to one allows the OC0A pin to toggle on compare matches if the WGM02 bit is
set. This option is not available for the OC0B pin (see Table 5-49 on page 108). The actual OC0x value will only be visible on
the port pin if the data direction for the port pin is set as output. The PWM waveform is generated by clearing (or setting) the
OC0x register at the compare match between OCR0x and TCNT0 when the counter increments, and setting (or clearing) the
OC0x register at compare match between OCR0x and TCNT0 when the counter decrements. The PWM frequency for the
output when using phase correct PWM can be calculated by the following equation:
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A register represent special cases when generating a PWM waveform output in the phase
correct PWM mode. If the OCR0A is set equal to BOTTOM, the output will be continuously low and if set equal to MAX the
output will be continuously high for non-inverted PWM mode. For inverted PWM the output will have the opposite logic
values.
At the very start of period 2 in Figure 5-33 on page 104 OCnx has a transition from high to low even though there is no
compare match. The point of this transition is to guarantee symmetry around BOTTOM. There are two cases that give a
transition without compare match.
●OCRnx changes its value from MAX, like in Figure 5-33 on page 104. When the OCR0A value is MAX the OCn pin
value is the same as the result of a down-counting compare match. To ensure symmetry around BOTTOM the OCnx
value at MAX must correspond to the result of an up-counting compare match.
●The timer starts counting from a value higher than the one in OCRnx, and for that reason misses the compare match
and hence the OCnx change that would have happened on the way up.
5.12.7 Timer/Counter Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkT0) is therefore shown as a clock enable signal in the
following figures. The figures include information on when interrupt flags are set. Figure 5-34 contains timing data for basic
Timer/Counter operation. The figure shows the count sequence close to the MAX value in all modes other than phase
correct PWM mode.
Figure 5-34. Timer/Counter Timing Diagram, no Prescaling
fOCnxPCPWM
fclk_I/O
N510×
-------------------
=
MAX - 1
clkI/O
(clkI/O/1)
TCNTn
TOVn
clkTn
MAX BOTTOM BOTTOM + 1
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Figure 5-35 shows the same timing data, but with the prescaler enabled.
Figure 5-35. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
Figure 5-36 shows the setting of OCF0B in all modes and OCF0A in all modes except CTC mode and PWM mode, where
OCR0A is TOP.
Figure 5-36. Timer/Counter Timing Diagram, Setting of OCF0x, with Prescaler (fclk_I/O/8)
Figure 5-37 shows the setting of OCF0A and the clearing of TCNT0 in CTC mode and fast PWM mode where OCR0A is
TOP.
Figure 5-37. Timer/Counter Timing Diagram, Clear Timer on Compare Match Mode, with Prescaler (fclk_I/O/8)
MAX - 1
clkI/O
(clkI/O/8)
TCNTn
TOVn
clkTn
MAX BOTTOM BOTTOM + 1
OCRnx - 1
clkI/O
(clkI/O/8)
TCNTn
OCRnx
OCFnx
clkTn
OCRnx OCRnx + 1
OCRnx Value
OCRnx + 2
TOP - 1
clkI/O
(clkI/O/8)
TCNTn
(CTC)
OCRnx
OCFnx
clkTn
TOP BOTTOM
TOP
BOTTOM + 1
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5.12.8 8-bit Timer/Counter Register Description
5.12.8.1 Timer/Counter Control Register A – TCCR0A
• Bits 7:6 – COM0A1:0: Compare Match Output A Mode
These bits control the output compare pin (OC0A) behavior. If one or both of the COM0A1:0 bits are set, the OC0A output
overrides the normal port functionality of the I/O pin it is connected to. However, note that the data direction register (DDR)
bit corresponding to the OC0A pin must be set in order to enable the output driver.
When OC0A is connected to the pin, the function of the COM0A1:0 bits depends on the WGM02:0 bit setting. Table 5-44
shows the COM0A1:0 bit functionality when the WGM02:0 bits are set to a normal or CTC mode (non-PWM).
Table 5-45 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to fast PWM mode.
Table 5-46 shows the COM0A1:0 bit functionality when the WGM02:0 bits are set to phase correct PWM mode.
Bit 7 6 5 4 3 2 1 0
COM0A1COM0A0COM0B1COM0B0––WGM01 WGM00 TCCR0A
Read/Write R/W R/W R/W R/W R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 5-44. Compare Output Mode, non-PWM Mode
COM0A1 COM0A0 Description
0 0 Normal port operation, OC0A disconnected.
0 1 Toggle OC0A on compare match
1 0 Clear OC0A on compare match
1 1 Set OC0A on compare match
Table 5-45. Compare Output Mode, Fast PWM Mode(1)
COM0A1 COM0A0 Description
0 0 Normal port operation, OC0A disconnected.
0 1 WGM02 = 0: Normal port operation, OC0A disconnected.
WGM02 = 1: Toggle OC0A on compare match.
1 0 Clear OC0A on compare match, set OC0A at TOP
1 1 Set OC0A on compare match, clear OC0A at TOP
Note: 1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the compare match is
ignored, but the set or clear is done at TOP. See Section 5.12.6.3 “Fast PWM Mode” on page 103 for more
details.
Table 5-46. Compare Output Mode, Phase Correct PWM Mode(1)
COM0A1 COM0A0 Description
0 0 Normal port operation, OC0A disconnected.
0 1 WGM02 = 0: Normal port operation, OC0A disconnected.
WGM02 = 1: Toggle OC0A on compare match.
1 0 Clear OC0A on compare match when up-counting. Set OC0A on compare match
when down-counting.
1 1 Set OC0A on compare match when up-counting. Clear OC0A on compare match
when down-counting.
Note: 1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the compare match is
ignored, but the set or clear is done at TOP. See Section 5.14.8.4 “Phase Correct PWM Mode” on page 127
for more details.
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• Bits 5:4 – COM0B1:0: Compare Match Output B Mode
These bits control the output compare pin (OC0B) behavior. If one or both of the COM0B1:0 bits are set, the OC0B output
overrides the normal port functionality of the I/O pin it is connected to. However, note that the data direction register (DDR)
bit corresponding to the OC0B pin must be set in order to enable the output driver.
When OC0B is connected to the pin, the function of the COM0B1:0 bits depends on the WGM02:0 bit setting. Table 5-47
shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to a normal or CTC mode (non-PWM).
Table 5-48 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to fast PWM mode.
Table 5-49 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to phase correct PWM mode.
• Bits 3, 2 – Res: Reserved Bits
These bits are reserved bits in the Atmel® ATA6612C/ATA6613C and will always read as zero.
• Bits 1:0 – WGM01:0: Waveform Generation Mode
Combined with the WGM02 bit found in the TCCR0B register, these bits control the counting sequence of the counter, the
source for maximum (TOP) counter value, and what type of waveform generation to be used (see Table 5-50 on page 109).
Modes of operation supported by the Timer/Counter unit are: Normal mode (counter), clear timer on compare match (CTC)
mode, and two types of pulse width modulation (PWM) modes (see Section 5.12.6 “Modes of Operation” on page 101).
Table 5-47. Compare Output Mode, non-PWM Mode
COM0B1 COM0B0 Description
0 0 Normal port operation, OC0B disconnected.
0 1 Toggle OC0B on compare match
1 0 Clear OC0B on compare match
1 1 Set OC0B on compare match
Table 5-48. Compare Output Mode, Fast PWM Mode(1)
COM0B1 COM0B0 Description
0 0 Normal port operation, OC0B disconnected.
0 1 Reserved
1 0 Clear OC0B on compare match, set OC0B at TOP
1 1 Set OC0B on compare match, clear OC0B at TOP
Note: 1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the compare match is
ignored, but the set or clear is done at TOP. See Section 5.12.6.3 “Fast PWM Mode” on page 103 for more
details.
Table 5-49. Compare Output Mode, Phase Correct PWM Mode(1)
COM0B1 COM0B0 Description
0 0 Normal port operation, OC0B disconnected.
0 1 Reserved
1 0 Clear OC0B on compare match when up-counting. Set OC0B on compare match
when down-counting.
1 1 Set OC0B on compare match when up-counting. Clear OC0B on compare match
when down-counting.
Note: 1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the compare match is
ignored, but the set or clear is done at TOP. See Section 5.12.6.4 “Phase Correct PWM Mode” on page 104
for more details.
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5.12.8.2 Timer/Counter Control Register B – TCCR0B
• Bit 7 – FOC0A: Force Output Compare A
The FOC0A bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when TCCR0B is written when operating
in PWM mode. When writing a logical one to the FOC0A bit, an immediate compare match is forced on the waveform
generation unit. The OC0A output is changed according to its COM0A1:0 bits setting. Note that the FOC0A bit is
implemented as a strobe. Therefore it is the value present in the COM0A1:0 bits that determines the effect of the forced
compare.
A FOC0A strobe will not generate any interrupt, nor will it clear the timer in CTC mode using OCR0A as TOP.
The FOC0A bit is always read as zero.
• Bit 6 – FOC0B: Force Output Compare B
The FOC0B bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when TCCR0B is written when operating
in PWM mode. When writing a logical one to the FOC0B bit, an immediate compare match is forced on the waveform
generation unit. The OC0B output is changed according to its COM0B1:0 bits setting. Note that the FOC0B bit is
implemented as a strobe. Therefore it is the value present in the COM0B1:0 bits that determines the effect of the forced
compare.
A FOC0B strobe will not generate any interrupt, nor will it clear the timer in CTC mode using OCR0B as TOP.
The FOC0B bit is always read as zero.
• Bits 5:4 – Res: Reserved Bits
These bits are reserved bits in the Atmel® ATA6612C/ATA6613C and will always read as zero.
• Bit 3 – WGM02: Waveform Generation Mode
See the description in the Section 5.12.8.1 “Timer/Counter Control Register A – TCCR0A” on page 107.
• Bits 2:0 – CS02:0: Clock Select
The three clock select bits select the clock source to be used by the Timer/Counter.
Table 5-50. Waveform Generation Mode Bit Description
Mode WGM02 WGM01 WGM00
Timer/Counter
Mode of Operation TOP
Update of
OCRx at
TOV Flag
Set on(1)(2)
0 0 0 0 Normal 0xFF Immediate MAX
1 0 0 1 PWM, phase correct 0xFF TOP BOTTOM
2 0 1 0 CTC OCRA Immediate MAX
3 0 1 1 Fast PWM 0xFF TOP MAX
4 1 0 0 Reserved – – –
5 1 0 1 PWM, phase correct OCRA TOP BOTTOM
6 1 1 0 Reserved – – –
7 1 1 1 Fast PWM OCRA TOP TOP
Notes: 1. MAX = 0xFF
2. BOTTOM = 0x00
Bit 7 6 5 4 3 210
FOC0A FOC0B – – WGM02 CS02 CS01 CS00 TCCR0B
Read/Write W W R R R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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If external pin modes are used for the Timer/Counter0, transitions on the T0 pin will clock the counter even if the pin is
configured as an output. This feature allows software control of the counting.
5.12.8.3 Timer/Counter Register – TCNT0
The Timer/Counter register gives direct access, both for read and write operations, to the Timer/Counter unit 8-bit counter.
Writing to the TCNT0 register blocks (removes) the compare match on the following timer clock. Modifying the counter
(TCNT0) while the counter is running, introduces a risk of missing a compare match between TCNT0 and the OCR0x
registers.
5.12.8.4 Output Compare Register A – OCR0A
The output compare register A contains an 8-bit value that is continuously compared with the counter value (TCNT0). A
match can be used to generate an output compare interrupt, or to generate a waveform output on the OC0A pin.
5.12.8.5 Output Compare Register B – OCR0B
The output compare register B contains an 8-bit value that is continuously compared with the counter value (TCNT0). A
match can be used to generate an output compare interrupt, or to generate a waveform output on the OC0B pin.
Table 5-51. Clock Select Bit Description
CS02 CS01 CS00 Description
000No clock source (Timer/Counter stopped)
001clkI/O/(no prescaling)
010clkI/O/8 (from prescaler)
011clkI/O/64 (from prescaler)
100clkI/O/256 (from prescaler)
101clkI/O/1024 (from prescaler)
110External clock source on T0 pin. Clock on falling edge.
111External clock source on T0 pin. Clock on rising edge.
Bit 76543210
TCNT0[7:0] TCNT0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
OCR0A[7:0] OCR0A
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
OCR0B[7:0] OCR0B
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
111
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5.12.8.6 Timer/Counter Interrupt Mask Register – TIMSK0
• Bits 7..3 – Res: Reserved Bits
These bits are reserved bits in the Atmel® ATA6612C/ATA6613C and will always read as zero.
• Bit 2 – OCIE0B: Timer/Counter Output Compare Match B Interrupt Enable
When the OCIE0B bit is written to one, and the I-bit in the status register is set, the Timer/Counter compare match B interrupt
is enabled. The corresponding interrupt is executed if a compare match in Timer/Counter occurs, i.e., when the OCF0B bit is
set in the Timer/Counter interrupt flag register – TIFR0.
• Bit 1 – OCIE0A: Timer/Counter0 Output Compare Match A Interrupt Enable
When the OCIE0A bit is written to one, and the I-bit in the status register is set, the Timer/Counter0 compare match A
interrupt is enabled. The corresponding interrupt is executed if a compare match in Timer/Counter0 occurs, i.e., when the
OCF0A bit is set in the Timer/Counter 0 interrupt flag register – TIFR0.
• Bit 0 – TOIE0: Timer/Counter0 Overflow Interrupt Enable
When the TOIE0 bit is written to one, and the I-bit in the status register is set, the Timer/Counter0 overflow interrupt is
enabled. The corresponding interrupt is executed if an overflow in Timer/Counter0 occurs, i.e., when the TOV0 bit is set in
the Timer/Counter 0 interrupt flag Register – TIFR0r
5.12.8.7 Timer/Counter 0 Interrupt Flag Register – TIFR0
• Bits 7..3 – Res: Reserved Bits
These bits are reserved bits in the Atmel ATA6612C/ATA6613C and will always read as zero.
• Bit 2 – OCF0B: Timer/Counter 0 Output Compare B Match Flag
The OCF0B bit is set when a compare match occurs between the Timer/Counter and the data in OCR0B – output compare
register0 B. OCF0B is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively,
OCF0B is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE0B (Timer/Counter compare B match
interrupt enable), and OCF0B are set, the Timer/Counter compare match interrupt is executed.
• Bit 1 – OCF0A: Timer/Counter 0 Output Compare A Match Flag
The OCF0A bit is set when a compare match occurs between the Timer/Counter0 and the data in OCR0A – output compare
register0. OCF0A is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF0A
is cleared by writing a logic one to the flag.
When the I-bit in SREG, OCIE0A (Timer/Counter0 compare match interrupt enable), and OCF0A are set, the
Timer/Counter0 compare match interrupt is executed.
• Bit 0 – TOV0: Timer/Counter0 Overflow Flag
The bit TOV0 is set when an overflow occurs in Timer/Counter0. TOV0 is cleared by hardware when executing the
corresponding interrupt handling vector. Alternatively, TOV0 is cleared by writing a logic one to the flag. When the
SREG I-bit, TOIE0 (Timer/Counter0 overflow interrupt enable), and TOV0 are set, the Timer/Counter0 overflow interrupt is
executed.
The setting of this flag is dependent of the WGM02:0 bit setting. Refer to Table 5-50 on page 109 and Section 5-50
“Waveform Generation Mode Bit Description” on page 109.
Bit 76543210
– – – – – OCIE0B OCIE0A TOIE0 TIMSK0
Read/Write R R R R R R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
–––––OCF0BOCF0ATOV0TIFR0
Read/Write RRRRRR/WR/WR/W
Initial Value00000000
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5.13 Timer/Counter0 and Timer/Counter1 Prescalers
Timer/Counter1 and Timer/Counter0 share the same prescaler module, but the Timer/Counters can have different prescaler
settings. The description below applies to both Timer/Counter1 and Timer/Counter0.
5.13.1 Internal Clock Source
The Timer/Counter can be clocked directly by the system clock (by setting the CSn2:0 = 1). This provides the fastest
operation, with a maximum Timer/Counter clock frequency equal to system clock frequency (fCLK_I/O). Alternatively, one of
four taps from the prescaler can be used as a clock source. The prescaled clock has a frequency of either fCLK_I/O/8,
fCLK_I/O/64, fCLK_I/O/256, or fCLK_I/O/1024.
5.13.2 Prescaler Reset
The prescaler is free running, i.e., operates independently of the clock select logic of the Timer/Counter, and it is shared by
Timer/Counter1 and Timer/Counter0. Since the prescaler is not affected by the Timer/Counter’s clock select, the state of the
prescaler will have implications for situations where a prescaled clock is used. One example of prescaling artifacts occurs
when the timer is enabled and clocked by the prescaler (6 > CSn2:0 > 1). The number of system clock cycles from when the
timer is enabled to the first count occurs can be from 1 to N+1 system clock cycles, where N equals the prescaler divisor (8,
64, 256, or 1024).
It is possible to use the prescaler reset for synchronizing the Timer/Counter to program execution. However, care must be
taken if the other Timer/Counter that shares the same prescaler also uses prescaling. A prescaler reset will affect the
prescaler period for all Timer/Counters it is connected to.
5.13.3 External Clock Source
An external clock source applied to the T1/T0 pin can be used as Timer/Counter clock (clkT1/clkT0). The T1/T0 pin is sampled
once every system clock cycle by the pin synchronization logic. The synchronized (sampled) signal is then passed through
the edge detector. Figure 5-38 shows a functional equivalent block diagram of the T1/T0 synchronization and edge detector
logic. The registers are clocked at the positive edge of the internal system clock (clkI/O). The latch is transparent in the high
period of the internal system clock.
The edge detector generates one clkT1/clkT0 pulse for each positive (CSn2:0 = 7) or negative (CSn2:0 = 6) edge it detects.
Figure 5-38. T1/T0 Pin Sampling
The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system clock cycles from an edge has been
applied to the T1/T0 pin to the counter is updated.
Enabling and disabling of the clock input must be done when T1/T0 has been stable for at least one system clock cycle,
otherwise it is a risk that a false Timer/Counter clock pulse is generated.
Each half period of the external clock applied must be longer than one system clock cycle to ensure correct sampling. The
external clock must be guaranteed to have less than half the system clock frequency (fExtClk < fclk_I/O/2) given a 50/50% duty
cycle. Since the edge detector uses sampling, the maximum frequency of an external clock it can detect is half the sampling
frequency (nyquist sampling theorem). However, due to variation of the system clock frequency and duty cycle caused by
oscillator source (crystal, resonator, and capacitors) tolerances, it is recommended that maximum frequency of an external
clock source is less than fclk_I/O/2.5.
An external clock source can not be prescaled.
Tn
Synchronization Edge Detector
Tn_sync
(To Clock
Select Logic)
Q
LE
D QD QD
clkI/O
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Figure 5-39. Prescaler for Timer/Counter0 and Timer/Counter1(1)
Note: 1. The synchronization logic on the input pins (T1/T0) is shown in Figure 5-38 on page 112.
5.13.4 General Timer/Counter Control Register – GTCCR
• Bit 7 – TSM: Timer/Counter Synchronization Mode
Writing the TSM bit to one activates the Timer/Counter synchronization mode. In this mode, the value that is written to the
PSRASY and PSRSYNC bits is kept, hence keeping the corresponding prescaler reset signals asserted. This ensures that
the corresponding Timer/Counters are halted and can be configured to the same value without the risk of one of them
advancing during configuration. When the TSM bit is written to zero, the PSRASY and PSRSYNC bits are cleared by
hardware, and the Timer/Counters start counting simultaneously.
• Bit 0 – PSRSYNC: Prescaler Reset
When this bit is one, Timer/Counter1 and Timer/Counter0 prescaler will be reset. This bit is normally cleared immediately by
hardware, except if the TSM bit is set. Note that Timer/Counter1 and Timer/Counter0 share the same prescaler and a reset
of this prescaler will affect both timers.
5.14 16-bit Timer/Counter1 with PWM
The 16-bit Timer/Counter unit allows accurate program execution timing (event management), wave generation, and signal
timing measurement. The main features are:
●True 16-bit design (i.e., allows 16-bit PWM)
●Two independent output compare units
●Double buffered output compare registers
●One input capture unit
●Input capture noise canceler
●Clear timer on compare match (auto reload)
●Glitch-free, phase correct pulse width modulator (PWM)
Timer/Counter1 Clock Source
clkT1
clkI/O
PSRSYNC
T0
10-bit T/C Prescaler
0
CS10
CK/8
CK/64
CK/256
CK/1024
CS11
CS12
Synchronization
Clear
T1 Synchronization
Timer/Counter0 Clock Source
clkT0
0
CS00
CS01
CS02
Bit 765432 1 0
TSM – – – – – PSRASY PSRSYNC GTCCR
Read/Write R/W R R R R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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●Variable PWM period
●Frequency generator
●External event counter
●Four independent interrupt sources (TOV1, OCF1A, OCF1B, and ICF1)
5.14.1 Overview
Most register and bit references in this section are written in general form. A lower case “n” replaces the Timer/Counter
number, and a lower case “x” replaces the output compare unit channel. However, when using the register or bit defines in a
program, the precise form must be used, i.e., TCNT1 for accessing Timer/Counter1 counter value and so on.
A simplified block diagram of the 16-bit Timer/Counter is shown in Figure 5-40 on page 114. The device-specific I/O register
and bit locations are listed in the Section 5.14.10 “16-bit Timer/Counter Register Description” on page 132.
The PRTIM1 bit in Section 5.7.7.1 “Power Reduction Register - PRR” on page 58 must be written to zero to enable
Timer/Counter1 module.
Figure 5-40. 16-bit Timer/Counter Block Diagram(1)
Note: 1. Refer to Table 5-32 on page 84 and Table 5-38 on page 89 for Timer/Counter1 pin placement and description.
Control Logic
TCNTn
Timer/Counter
Count
Clear
Direction
clkTn
OCRnA
OCRnB
ICRn
TCCRnA TCCRnB
=
Edge
Detector
(from Prescaler)
Clock Select
TOP BOTTOM
TOVn (Int. Req.)
OCnA (Int. Req.)
Tn
Waveform
Generation
Fixed
TOP
Value
DATA BUS
=
== 0
OCnA
OCnB (Int. Req.)
Waveform
Generation
Noise
Canceler
OCnB
(From Analog
Comparator Output)
ICFn (Int. Req.)
Edge
Detector ICPn
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5.14.1.1 Registers
The Timer/Counter (TCNT1), output compare registers (OCR1A/B), and input capture register (ICR1) are all 16-bit registers.
Special procedures must be followed when accessing the 16-bit registers. These procedures are described in the
Section 5.14.2 “Accessing 16-bit Registers” on page 115. The Timer/Counter control registers (TCCR1A/B) are 8-bit
registers and have no CPU access restrictions. Interrupt requests (abbreviated to Int.Req. in the figure) signals are all visible
in the timer interrupt flag register (TIFR1). All interrupts are individually masked with the timer interrupt mask register
(TIMSK1). TIFR1 and TIMSK1 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on the T1 pin. The clock select
logic block controls which clock source and edge the Timer/Counter uses to increment (or decrement) its value. The
Timer/Counter is inactive when no clock source is selected. The output from the clock select logic is referred to as the timer
clock (clkT1).
The double buffered output compare registers (OCR1A/B) are compared with the Timer/Counter value at all time. The result
of the compare can be used by the waveform generator to generate a PWM or variable frequency output on the output
compare pin (OC1A/B), see Section 5.14.6 “Output Compare Units” on page 121. The compare match event will also set the
compare match flag (OCF1A/B) which can be used to generate an output compare interrupt request.
The input capture register can capture the Timer/Counter value at a given external (edge triggered) event on either the input
capture pin (ICP1) or on the analog comparator pins (see Section 5.20 “Analog Comparator” on page 221). The input
capture unit includes a digital filtering unit (noise canceler) for reducing the chance of capturing noise spikes.
The TOP value, or maximum Timer/Counter value, can in some modes of operation be defined by either the OCR1A
register, the ICR1 register, or by a set of fixed values. When using OCR1A as TOP value in a PWM mode, the OCR1A
register can not be used for generating a PWM output. However, the TOP value will in this case be double buffered allowing
the TOP value to be changed in run time. If a fixed TOP value is required, the ICR1 register can be used as an alternative,
freeing the OCR1A to be used as PWM output.
5.14.1.2 Definitions
The following definitions are used extensively throughout the section:
5.14.2 Accessing 16-bit Registers
The TCNT1, OCR1A/B, and ICR1 are 16-bit registers that can be accessed by the AVR® CPU via the 8-bit data bus. The
16-bit register must be byte accessed using two read or write operations. Each 16-bit timer has a single 8-bit register for
temporary storing of the high byte of the 16-bit access. The same temporary register is shared between all 16-bit registers
within each 16-bit timer. Accessing the low byte triggers the 16-bit read or write operation. When the low byte of a 16-bit
register is written by the CPU, the high byte stored in the temporary register, and the low byte written are both copied into the
16-bit register in the same clock cycle. When the low byte of a 16-bit register is read by the CPU, the high byte of the 16-bit
register is copied into the temporary register in the same clock cycle as the low byte is read.
Not all 16-bit accesses uses the temporary register for the high byte. Reading the OCR1A/B 16-bit registers does not involve
using the temporary register.
To do a 16-bit write, the high byte must be written before the low byte. For a 16-bit read, the low byte must be read before the
high byte.
Table 5-52. General Counter Definitions
Parameter Definition
BOTTOM The counter reaches the BOTTOM when it becomes 0x0000.
MAX The counter reaches its MAXimum when it becomes 0xFFFF (decimal 65535).
TOP
The counter reaches the TOP when it becomes equal to the highest value in the count sequence. The TOP
value can be assigned to be one of the fixed values: 0x00FF, 0x01FF, or 0x03FF, or to the value stored in
the OCR1A or ICR1 register. The assignment is dependent of the mode of operation.
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The following code examples show how to access the 16-bit timer registers assuming that no interrupts updates the
temporary register. The same principle can be used directly for accessing the OCR1A/B and ICR1 registers. Note that when
using “C”, the compiler handles the 16-bit access.
Note: 1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must
be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with
“SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example returns the TCNT1 value in the r17:r16 register pair.
It is important to notice that accessing 16-bit registers are atomic operations. If an interrupt occurs between the two
instructions accessing the 16-bit register, and the interrupt code updates the temporary register by accessing the same or
any other of the 16-bit timer registers, then the result of the access outside the interrupt will be corrupted. Therefore, when
both the main code and the interrupt code update the temporary register, the main code must disable the interrupts during
the 16-bit access.
Assembly Code Examples(1)
...
; Set TCNT1 to 0x01FF
ldi r17,0x01
ldi r16,0xFF
out TCNT1H,r17
out TCNT1L,r16
; Read TCNT1 into r17:r16
in r16,TCNT1L
in r17,TCNT1H
...
C Code Examples(1)
unsigned int i;
...
/* Set TCNT1 to 0x01FF */
TCNT1 = 0x1FF;
/* Read TCNT1 into i */
i = TCNT1;
...
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The following code examples show how to do an atomic read of the TCNT1 register contents. Reading any of the OCR1A/B
or ICR1 registers can be done by using the same principle.
Note: 1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must
be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with
“SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example returns the TCNT1 value in the r17:r16 register pair.
Assembly Code Example(1)
TIM16_ReadTCNT1:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Read TCNT1 into r17:r16
in r16,TCNT1L
in r17,TCNT1H
; Restore global interrupt flag
out SREG,r18
ret
C Code Example(1)
unsigned int TIM16_ReadTCNT1( void )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Read TCNT1 into i */
i = TCNT1;
/* Restore global interrupt flag */
SREG = sreg;
return i;
}
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The following code examples show how to do an atomic write of the TCNT1 register contents. Writing any of the OCR1A/B
or ICR1 registers can be done by using the same principle.
Note: 1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must
be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with
“SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example requires that the r17:r16 register pair contains the value to be written to TCNT1.
5.14.2.1 Reusing the Temporary High Byte Register
If writing to more than one 16-bit register where the high byte is the same for all registers written, then the high byte only
needs to be written once. However, note that the same rule of atomic operation described previously also applies in this
case.
5.14.3 Timer/Counter Clock Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock source is selected by the clock
select logic which is controlled by the clock select (CS12:0) bits located in the Timer/Counter control register B (TCCR1B).
For details on clock sources and prescaler (see Section 5.13 “Timer/Counter0 and Timer/Counter1 Prescalers” on page
112).
Assembly Code Example(1)
TIM16_WriteTCNT1:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Set TCNT1 to r17:r16
out TCNT1H,r17
out TCNT1L,r16
; Restore global interrupt flag
out SREG,r18
ret
C Code Example(1)
void TIM16_WriteTCNT1(unsigned int i)
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Set TCNT1 to i */
TCNT1 = i;
/* Restore global interrupt flag */
SREG = sreg;
}
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5.14.4 Counter Unit
The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional counter unit. Figure 5-41 shows a block
diagram of the counter and its surroundings.
Figure 5-41. Counter Unit Block Diagram
Signal description (internal signals):
Count Increment or decrement TCNT1 by 1.
Direction Select between increment and decrement.
Clear Clear TCNT1 (set all bits to zero).
clkT1 Timer/Counter clock.
TOP Signalize that TCNT1 has reached maximum value.
BOTTOM Signalize that TCNT1 has reached minimum value (zero).
The 16-bit counter is mapped into two 8-bit I/O memory locations: Counter High (TCNT1H) containing the upper eight bits of
the counter, and counter low (TCNT1L) containing the lower eight bits. The TCNT1H register can only be indirectly accessed
by the CPU. When the CPU does an access to the TCNT1H I/O location, the CPU accesses the high byte temporary register
(TEMP). The temporary register is updated with the TCNT1H value when the TCNT1L is read, and TCNT1H is updated with
the temporary register value when TCNT1L is written. This allows the CPU to read or write the entire 16-bit counter value
within one clock cycle via the 8-bit data bus. It is important to notice that there are special cases of writing to the TCNT1
register when the counter is counting that will give unpredictable results. The special cases are described in the sections
where they are of importance.
Depending on the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clkT1).
The clkT1 can be generated from an external or internal clock source, selected by the clock select bits (CS12:0). When no
clock source is selected (CS12:0 = 0) the timer is stopped. However, the TCNT1 value can be accessed by the CPU,
independent of whether clkT1 is present or not. A CPU write overrides (has priority over) all counter clear or count
operations.
The counting sequence is determined by the setting of the waveform generation mode bits (WGM13:0) located in the
Timer/Counter control registers A and B (TCCR1A and TCCR1B). There are close connections between how the counter
behaves (counts) and how waveforms are generated on the output compare outputs OC1x. For more details about
advanced counting sequences and waveform generation (see Section 5.14.8 “Modes of Operation” on page 124).
The Timer/Counter overflow flag (TOV1) is set according to the mode of operation selected by the WGM13:0 bits. TOV1 can
be used for generating a CPU interrupt.
5.14.5 Input Capture Unit
The Timer/Counter incorporates an input capture unit that can capture external events and give them a time-stamp
indicating time of occurrence. The external signal indicating an event, or multiple events, can be applied via the ICP1 pin or
alternatively, via the analog-comparator unit. The time-stamps can then be used to calculate frequency, duty-cycle, and
other features of the signal applied. Alternatively the time-stamps can be used for creating a log of the events.
The input capture unit is illustrated by the block diagram shown in Figure 5-42 on page 120. The elements of the block
diagram that are not directly a part of the input capture unit are gray shaded. The small “n” in register and bit names
indicates the Timer/Counter number.
BOTTOMTOP
TOVn
(Int. Req.)
DATA BUS (8-bit)
Control Logic
TCNTnH (8-bit)
TCNTnH (16-bit Counter)
TCNTnL (8-bit)
TEMP (8-bit)
clkTn
Clear
Count
Direction
Edge
Detector
(From Prescaler)
Clock Select
Tn
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Figure 5-42. Input Capture Unit Block Diagram
When a change of the logic level (an event) occurs on the input capture pin (ICP1), alternatively on the analog comparator
output (ACO), and this change confirms to the setting of the edge detector, a capture will be triggered. When a capture is
triggered, the 16-bit value of the counter (TCNT1) is written to the input capture register (ICR1). The input capture flag (ICF1)
is set at the same system clock as the TCNT1 value is copied into ICR1 register. If enabled (ICIE1 = 1), the input capture flag
generates an input capture interrupt. The ICF1 flag is automatically cleared when the interrupt is executed. Alternatively the
ICF1 flag can be cleared by software by writing a logical one to its I/O bit location.
Reading the 16-bit value in the input capture register (ICR1) is done by first reading the low byte (ICR1L) and then the high
byte (ICR1H). When the low byte is read the high byte is copied into the high byte temporary register (TEMP). When the
CPU reads the ICR1H I/O location it will access the TEMP register.
The ICR1 register can only be written when using a waveform generation mode that utilizes the ICR1 register for defining the
counter’s TOP value. In these cases the waveform generation mode (WGM13:0) bits must be set before the TOP value can
be written to the ICR1 register. When writing the ICR1 register the high byte must be written to the ICR1H I/O location before
the low byte is written to ICR1L.
For more information on how to access the 16-bit registers refer to Section 5.14.2 “Accessing 16-bit Registers” on page 115.
5.14.5.1 Input Capture Trigger Source
The main trigger source for the input capture unit is the input capture pin (ICP1). Timer/Counter1 can alternatively use the
analog comparator output as trigger source for the input capture unit. The analog comparator is selected as trigger source by
setting the analog comparator input capture (ACIC) bit in the analog comparator control and status register (ACSR). Be
aware that changing trigger source can trigger a capture. The input capture flag must therefore be cleared after the change.
Both the input capture pin (ICP1) and the analog comparator output (ACO) inputs are sampled using the same technique as
for the T1 pin (see Figure 5-38 on page 112). The edge detector is also identical. However, when the noise canceler is
enabled, additional logic is inserted before the edge detector, which increases the delay by four system clock cycles. Note
that the input of the noise canceler and edge detector is always enabled unless the Timer/Counter is set in a waveform
generation mode that uses ICR1 to define TOP.
An input capture can be triggered by software by controlling the port of the ICP1 pin.
ICFn (Int. Req.)
ICRnL (8-bit)ICRnH (8-bit)
ICRn (16-bit Register)
TEMP (8-bit)
TCNTnL (8-bit)TCNTnH (8-bit)
TCNTn (16-bit Counter)
DATA BUS (8-bit)
Noise
Canceler
Analog
Comparator Edge
Detector
ICNCnACIC*
ACO*
WRITE
+
-
ICESn
ICPn
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5.14.5.2 Noise Canceler
The noise canceler improves noise immunity by using a simple digital filtering scheme. The noise canceler input is monitored
over four samples, and all four must be equal for changing the output that in turn is used by the edge detector.
The noise canceler is enabled by setting the input capture noise canceler (ICNC1) bit in Timer/Counter control register B
(TCCR1B). When enabled the noise canceler introduces additional four system clock cycles of delay from a change applied
to the input, to the update of the ICR1 register. The noise canceler uses the system clock and is therefore not affected by the
prescaler.
5.14.5.3 Using the Input Capture Unit
The main challenge when using the input capture unit is to assign enough processor capacity for handling the incoming
events. The time between two events is critical. If the processor has not read the captured value in the ICR1 register before
the next event occurs, the ICR1 will be overwritten with a new value. In this case the result of the capture will be incorrect.
When using the input capture interrupt, the ICR1 register should be read as early in the interrupt handler routine as possible.
Even though the input capture interrupt has relatively high priority, the maximum interrupt response time is dependent on the
maximum number of clock cycles it takes to handle any of the other interrupt requests.
Using the input capture unit in any mode of operation when the TOP value (resolution) is actively changed during operation,
is not recommended.
Measurement of an external signal’s duty cycle requires that the trigger edge is changed after each capture. Changing the
edge sensing must be done as early as possible after the ICR1 register has been read. After a change of the edge, the input
capture flag (ICF1) must be cleared by software (writing a logical one to the I/O bit location). For measuring frequency only,
the clearing of the ICF1 flag is not required (if an interrupt handler is used).
5.14.6 Output Compare Units
The 16-bit comparator continuously compares TCNT1 with the output compare register (OCR1x). If TCNT equals OCR1x
the comparator signals a match. A match will set the output compare flag (OCF1x) at the next timer clock cycle. If enabled
(OCIE1x = 1), the output compare flag generates an output compare interrupt. The OCF1x flag is automatically cleared
when the interrupt is executed. Alternatively the OCF1x flag can be cleared by software by writing a logical one to its I/O bit
location. The waveform generator uses the match signal to generate an output according to operating mode set by the
waveform generation mode (WGM13:0) bits and compare output mode (COM1x1:0) bits. The TOP and BOTTOM signals
are used by the waveform generator for handling the special cases of the extreme values in some modes of operation (see
Section 5.14.8 “Modes of Operation” on page 124).
A special feature of output compare unit A allows it to define the Timer/Counter TOP value (i.e., counter resolution). In
addition to the counter resolution, the TOP value defines the period time for waveforms generated by the waveform
generator.
Figure 5-43 on page 122 shows a block diagram of the output compare unit. The small “n” in the register and bit names
indicates the device number (n = 1 for Timer/Counter 1), and the “x” indicates output compare unit (A/B). The elements of the
block diagram that are not directly a part of the output compare unit are gray shaded.
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Figure 5-43. Output Compare Unit, Block Diagram
The OCR1x register is double buffered when using any of the twelve pulse width modulation (PWM) modes. For the normal
and clear timer on compare (CTC) modes of operation, the double buffering is disabled. The double buffering synchronizes
the update of the OCR1x compare register to either TOP or BOTTOM of the counting sequence. The synchronization
prevents the occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
The OCR1x register access may seem complex, but this is not case. When the double buffering is enabled, the CPU has
access to the OCR1x buffer register, and if double buffering is disabled the CPU will access the OCR1x directly. The content
of the OCR1x (buffer or compare) register is only changed by a write operation (the Timer/Counter does not update this
register automatically as the TCNT1 and ICR1 register). Therefore OCR1x is not read via the high byte temporary register
(TEMP). However, it is a good practice to read the low byte first as when accessing other 16-bit registers. Writing the OCR1x
registers must be done via the TEMP register since the compare of all 16 bits is done continuously. The high byte (OCR1xH)
has to be written first. When the high byte I/O location is written by the CPU, the TEMP register will be updated by the value
written. Then when the low byte (OCR1xL) is written to the lower eight bits, the high byte will be copied into the upper 8-bits
of either the OCR1x buffer or OCR1x compare register in the same system clock cycle. For more information of how to
access the 16-bit registers refer to Section 5.14.2 “Accessing 16-bit Registers” on page 115.
5.14.6.1 Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced by writing a one to the force
output compare (FOC1x) bit. Forcing compare match will not set the OCF1x flag or reload/clear the timer, but the OC1x pin
will be updated as if a real compare match had occurred (the COM11:0 bits settings define whether the OC1x pin is set,
cleared or toggled).
5.14.6.2 Compare Match Blocking by TCNT1 Write
All CPU writes to the TCNT1 register will block any compare match that occurs in the next timer clock cycle, even when the
timer is stopped. This feature allows OCR1x to be initialized to the same value as TCNT1 without triggering an interrupt
when the Timer/Counter clock is enabled.
OCRnxL Buf. (8-bit)OCRnxH Buf. (8-bit)
OCRnx Buffer (16-bit Register)
TEMP (8-bit)
OCRnxL (8-bit)
OCFnx (Int. Req.)
OCRnxH (8-bit)
OCRnx (16-bit Register)
= (16-bit Comparator)
WGMn3:0 COMnx1:0
Waveform Generator
TCNTnL (8-bit)TCNTnH (8-bit)
TCNTn (16-bit Counter)
DATA BUS
(8-bit)
OCnx
TOP
BOTTOM
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5.14.6.3 Using the Output Compare Unit
Since writing TCNT1 in any mode of operation will block all compare matches for one timer clock cycle, there are risks
involved when changing TCNT1 when using any of the output compare channels, independent of whether the Timer/Counter
is running or not. If the value written to TCNT1 equals the OCR1x value, the compare match will be missed, resulting in
incorrect waveform generation. Do not write the TCNT1 equal to TOP in PWM modes with variable TOP values. The
compare match for the TOP will be ignored and the counter will continue to 0xFFFF. Similarly, do not write the TCNT1 value
equal to BOTTOM when the counter is downcounting.
The setup of the OC1x should be performed before setting the data direction register for the port pin to output. The easiest
way of setting the OC1x value is to use the force output compare (FOC1x) strobe bits in normal mode. The OC1x register
keeps its value even when changing between waveform generation modes. Be aware that the COM1x1:0 bits are not double
buffered together with the compare value. Changing the COM1x1:0 bits will take effect immediately.
5.14.7 Compare Match Output Unit
The compare output mode (COM1x1:0) bits have two functions. The waveform generator uses the COM1x1:0 bits for
defining the output compare (OC1x) state at the next compare match. Secondly the COM1x1:0 bits control the OC1x pin
output source. Figure 5-44 shows a simplified schematic of the logic affected by the COM1x1:0 bit setting. The I/O registers,
I/O bits, and I/O pins in the figure are shown in bold. Only the parts of the general I/O port control registers (DDR and PORT)
that are affected by the COM1x1:0 bits are shown. When referring to the OC1x state, the reference is for the internal OC1x
register, not the OC1x pin. If a system reset occur, the OC1x register is reset to “0”.
Figure 5-44. Compare Match Output Unit, Schematic
The general I/O port function is overridden by the output compare (OC1x) from the waveform generator if either of the
COM1x1:0 bits are set. However, the OC1x pin direction (input or output) is still controlled by the data direction register
(DDR) for the port pin. The data direction register bit for the OC1x pin (DDR_OC1x) must be set as output before the OC1x
value is visible on the pin. The port override function is generally independent of the waveform generation mode, but there
are some exceptions. Refer to Table 5-53 on page 132, Table 5-54 on page 132 and Table 5-55 on page 133 for details.
The design of the output compare pin logic allows initialization of the OC1x state before the output is enabled. Note that
some COM1x1:0 bit settings are reserved for certain modes of operation (see Section 5.14.10 “16-bit Timer/Counter
Register Description” on page 132).
The COM1x1:0 bits have no effect on the input capture unit.
DATA BUS
0
1
QD
COMnx1
COMnx0
FOCnx
OCnx
Waveform
Generator
QD
PORT
QD
DDR
OCnx
Pin
clkI/O
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5.14.7.1 Compare Output Mode and Waveform Generation
The waveform generator uses the COM1x1:0 bits differently in normal, CTC, and PWM modes. For all modes, setting the
COM1x1:0 = 0 tells the waveform generator that no action on the OC1x register is to be performed on the next compare
match. For compare output actions in the non-PWM modes refer to Table 5-53 on page 132. For fast PWM mode refer to
Table 5-54 on page 132, and for phase correct and phase and frequency correct PWM refer to Table 5-55 on page 133.
A change of the COM1x1:0 bits state will have effect at the first compare match after the bits are written. For non-PWM
modes, the action can be forced to have immediate effect by using the FOC1x strobe bits.
5.14.8 Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the output compare pins, is defined by the combination of
the waveform generation mode (WGM13:0) and compare output mode (COM1x1:0) bits. The compare output mode bits do
not affect the counting sequence, while the waveform generation mode bits do. The COM1x1:0 bits control whether the
PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes the COM1x1:0 bits
control whether the output should be set, cleared or toggle at a compare match (see Section 5.14.7 “Compare Match Output
Unit” on page 123).
For detailed timing information refer to Section 5.14.9 “Timer/Counter Timing Diagrams” on page 130.
5.14.8.1 Normal Mode
The simplest mode of operation is the normal mode (WGM13:0 = 0). In this mode the counting direction is always up
(incrementing), and no counter clear is performed. The counter simply overruns when it passes its maximum 16-bit value
(MAX = 0xFFFF) and then restarts from the BOTTOM (0x0000). In normal operation the Timer/Counter overflow flag (TOV1)
will be set in the same timer clock cycle as the TCNT1 becomes zero. The TOV1 flag in this case behaves like a 17th bit,
except that it is only set, not cleared. However, combined with the timer overflow interrupt that automatically clears the TOV1
flag, the timer resolution can be increased by software. There are no special cases to consider in the normal mode, a new
counter value can be written anytime.
The input capture unit is easy to use in normal mode. However, observe that the maximum interval between the external
events must not exceed the resolution of the counter. If the interval between events are too long, the timer overflow interrupt
or the prescaler must be used to extend the resolution for the capture unit.
The output compare units can be used to generate interrupts at some given time. Using the output compare to generate
waveforms in normal mode is not recommended, since this will occupy too much of the CPU time.
5.14.8.2 Clear Timer on Compare Match (CTC) Mode
In clear timer on compare or CTC mode (WGM13:0 = 4 or 12), the OCR1A or ICR1 register are used to manipulate the
counter resolution. In CTC mode the counter is cleared to zero when the counter value (TCNT1) matches either the OCR1A
(WGM13:0 = 4) or the ICR1 (WGM13:0 = 12). The OCR1A or ICR1 define the top value for the counter, hence also its
resolution. This mode allows greater control of the compare match output frequency. It also simplifies the operation of
counting external events.
The timing diagram for the CTC mode is shown in Figure 5-45. The counter value (TCNT1) increases until a compare match
occurs with either OCR1A or ICR1, and then counter (TCNT1) is cleared.
Figure 5-45. CTC Mode, Timing Diagram
12
TCNTn
(COMnA1:0 = 1)
OCnA
(Toggle)
Period 3
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
4
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An interrupt can be generated at each time the counter value reaches the TOP value by either using the OCF1A or ICF1 flag
according to the register used to define the TOP value. If the interrupt is enabled, the interrupt handler routine can be used
for updating the TOP value. However, changing the TOP to a value close to BOTTOM when the counter is running with none
or a low prescaler value must be done with care since the CTC mode does not have the double buffering feature. If the new
value written to OCR1A or ICR1 is lower than the current value of TCNT1, the counter will miss the compare match. The
counter will then have to count to its maximum value (0xFFFF) and wrap around starting at 0x0000 before the compare
match can occur. In many cases this feature is not desirable. An alternative will then be to use the fast PWM mode using
OCR1A for defining TOP (WGM13:0 = 15) since the OCR1A then will be double buffered.
For generating a waveform output in CTC mode, the OC1A output can be set to toggle its logical level on each compare
match by setting the compare output mode bits to toggle mode (COM1A1:0 = 1). The OC1A value will not be visible on the
port pin unless the data direction for the pin is set to output (DDR_OC1A = 1). The waveform generated will have a
maximum frequency of fOC1A = fclk_I/O/2 when OCR1A is set to zero (0x0000). The waveform frequency is defined by the
following equation:
The N variable represents the prescaler factor (1, 8, 64, 256, or 1024).
As for the normal mode of operation, the TOV1 flag is set in the same timer clock cycle that the counter counts from MAX to
0x0000.
5.14.8.3 Fast PWM Mode
The fast pulse width modulation or fast PWM mode (WGM13:0 = 5, 6, 7, 14, or 15) provides a high frequency PWM
waveform generation option. The fast PWM differs from the other PWM options by its single-slope operation. The counter
counts from BOTTOM to TOP then restarts from BOTTOM. In non-inverting compare output mode, the output compare
(OC1x) is set on the compare match between TCNT1 and OCR1x, and cleared at TOP. In inverting compare output mode
output is cleared on compare match and set at TOP. Due to the single-slope operation, the operating frequency of the fast
PWM mode can be twice as high as the phase correct and phase and frequency correct PWM modes that use dual-slope
operation. This high frequency makes the fast PWM mode well suited for power regulation, rectification, and DAC
applications. High frequency allows physically small sized external components (coils, capacitors), hence reduces total
system cost.
The PWM resolution for fast PWM can be fixed to 8-, 9-, or 10-bit, or defined by either ICR1 or OCR1A. The minimum
resolution allowed is 2-bit (ICR1 or OCR1A set to 0x0003), and the maximum resolution is 16-bit (ICR1 or OCR1A set to
MAX). The PWM resolution in bits can be calculated by using the following equation:
In fast PWM mode the counter is incremented until the counter value matches either one of the fixed values 0x00FF,
0x01FF, or 0x03FF (WGM13:0 = 5, 6, or 7), the value in ICR1 (WGM13:0 = 14), or the value in OCR1A (WGM13:0 = 15).
The counter is then cleared at the following timer clock cycle. The timing diagram for the fast PWM mode is shown in
Figure 5-46 on page 126. The figure shows fast PWM mode when OCR1A or ICR1 is used to define TOP. The TCNT1 value
is in the timing diagram shown as a histogram for illustrating the single-slope operation. The diagram includes non-inverted
and inverted PWM outputs. The small horizontal line marks on the TCNT1 slopes represent compare matches between
OCR1x and TCNT1. The OC1x interrupt flag will be set when a compare match occurs.
fOCnA
fclk_I/O
2 N 1 OCRnA+()××
-----------------------------------------------------
=
RFPWM
log TOP 1+()
log 2()
---------------------------------
=
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Figure 5-46. Fast PWM Mode, Timing Diagram
The Timer/Counter overflow flag (TOV1) is set each time the counter reaches TOP. In addition the OC1A or ICF1 flag is set
at the same timer clock cycle as TOV1 is set when either OCR1A or ICR1 is used for defining the TOP value. If one of the
interrupts are enabled, the interrupt handler routine can be used for updating the TOP and compare values.
When changing the TOP value the program must ensure that the new TOP value is higher or equal to the value of all of the
compare registers. If the TOP value is lower than any of the compare registers, a compare match will never occur between
the TCNT1 and the OCR1x. Note that when using fixed TOP values the unused bits are masked to zero when any of the
OCR1x registers are written.
The procedure for updating ICR1 differs from updating OCR1A when used for defining the TOP value. The ICR1 register is
not double buffered. This means that if ICR1 is changed to a low value when the counter is running with none or a low
prescaler value, there is a risk that the new ICR1 value written is lower than the current value of TCNT1. The result will then
be that the counter will miss the compare match at the TOP value. The counter will then have to count to the MAX value
(0xFFFF) and wrap around starting at 0x0000 before the compare match can occur. The OCR1A register however, is double
buffered. This feature allows the OCR1A I/O location to be written anytime. When the OCR1A I/O location is written the
value written will be put into the OCR1A buffer register. The OCR1A compare register will then be updated with the value in
the buffer register at the next timer clock cycle the TCNT1 matches TOP. The update is done at the same timer clock cycle
as the TCNT1 is cleared and the TOV1 flag is set.
Using the ICR1 register for defining TOP works well when using fixed TOP values. By using ICR1, the OCR1A register is
free to be used for generating a PWM output on OC1A. However, if the base PWM frequency is actively changed (by
changing the TOP value), using the OCR1A as TOP is clearly a better choice due to its double buffer feature.
In fast PWM mode, the compare units allow generation of PWM waveforms on the OC1x pins. Setting the COM1x1:0 bits to
two will produce a non-inverted PWM and an inverted PWM output can be generated by setting the COM1x1:0 to three (see
Table 5-53 on page 132). The actual OC1x value will only be visible on the port pin if the data direction for the port pin is set
as output (DDR_OC1x). The PWM waveform is generated by setting (or clearing) the OC1x register at the compare match
between OCR1x and TCNT1, and clearing (or setting) the OC1x register at the timer clock cycle the counter is cleared
(changes from TOP to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCR1x register represents special cases when generating a PWM waveform output in the fast
PWM mode. If the OCR1x is set equal to BOTTOM (0x0000) the output will be a narrow spike for each TOP+1 timer clock
cycle. Setting the OCR1x equal to TOP will result in a constant high or low output (depending on the polarity of the output set
by the COM1x1:0 bits).
12345
TCNTn
(COMnx1:0 = 2)
OCnx
OCnx
Period
OCRnx/TOP Update and
TOVn Interrupt Flag Set and
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
67 8
(COMnx1:0 = 3)
fOCnxPWM
fclk_I/O
N1TOP+()×
------------------------------------
=
127
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OC1A to toggle its logical
level on each compare match (COM1A1:0 = 1). This applies only if OCR1A is used to define the TOP value
(WGM13:0 = 15). The waveform generated will have a maximum frequency of fOC1A = fclk_I/O/2 when OCR1A is set to zero
(0x0000). This feature is similar to the OC1A toggle in CTC mode, except the double buffer feature of the output compare
unit is enabled in the fast PWM mode.
5.14.8.4 Phase Correct PWM Mode
The phase correct pulse width modulation or phase correct PWM mode (WGM13:0 = 1, 2, 3, 10, or 11) provides a high
resolution phase correct PWM waveform generation option. The phase correct PWM mode is, like the phase and frequency
correct PWM mode, based on a dual-slope operation. The counter counts repeatedly from BOTTOM (0x0000) to TOP and
then from TOP to BOTTOM. In non-inverting compare output mode, the output compare (OC1x) is cleared on the compare
match between TCNT1 and OCR1x while upcounting, and set on the compare match while downcounting. In inverting output
compare mode, the operation is inverted. The dual-slope operation has lower maximum operation frequency than single
slope operation. However, due to the symmetric feature of the dual-slope PWM modes, these modes are preferred for motor
control applications.
The PWM resolution for the phase correct PWM mode can be fixed to 8-, 9-, or 10-bit, or defined by either ICR1 or OCR1A.
The minimum resolution allowed is 2-bit (ICR1 or OCR1A set to 0x0003), and the maximum resolution is 16-bit (ICR1 or
OCR1A set to MAX). The PWM resolution in bits can be calculated by using the following equation:
In phase correct PWM mode the counter is incremented until the counter value matches either one of the fixed values
0x00FF, 0x01FF, or 0x03FF (WGM13:0 = 1, 2, or 3), the value in ICR1 (WGM13:0 = 10), or the value in OCR1A
(WGM13:0 = 11). The counter has then reached the TOP and changes the count direction. The TCNT1 value will be equal to
TOP for one timer clock cycle. The timing diagram for the phase correct PWM mode is shown on Figure 5-47. The figure
shows phase correct PWM mode when OCR1A or ICR1 is used to define TOP. The TCNT1 value is in the timing diagram
shown as a histogram for illustrating the dual-slope operation. The diagram includes non-inverted and inverted PWM
outputs. The small horizontal line marks on the TCNT1 slopes represent compare matches between OCR1x and TCNT1.
The OC1x interrupt flag will be set when a compare match occurs.
Figure 5-47. Phase Correct PWM Mode, Timing Diagram
RPCPWM
log TOP 1+()
log 2()
---------------------------------
=
123 4
TCNTn
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCnx
OCnx
Period
TOVn Interrupt Flag Set
(Interrupt on Bottom)
OCRnx/TOP Update and
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
128
The Timer/Counter overflow flag (TOV1) is set each time the counter reaches BOTTOM. When either OCR1A or ICR1 is
used for defining the TOP value, the OC1A or ICF1 flag is set accordingly at the same timer clock cycle as the OCR1x
registers are updated with the double buffer value (at TOP). The interrupt flags can be used to generate an interrupt each
time the counter reaches the TOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is higher or equal to the value of all of the
compare registers. If the TOP value is lower than any of the compare registers, a compare match will never occur between
the TCNT1 and the OCR1x. Note that when using fixed TOP values, the unused bits are masked to zero when any of the
OCR1x registers are written. As the third period shown in Figure 5-47 on page 127 illustrates, changing the TOP actively
while the Timer/Counter is running in the phase correct mode can result in an unsymmetrical output. The reason for this can
be found in the time of update of the OCR1x register. Since the OCR1x update occurs at TOP, the PWM period starts and
ends at TOP. This implies that the length of the falling slope is determined by the previous TOP value, while the length of the
rising slope is determined by the new TOP value. When these two values differ the two slopes of the period will differ in
length. The difference in length gives the unsymmetrical result on the output.
It is recommended to use the phase and frequency correct mode instead of the phase correct mode when changing the TOP
value while the Timer/Counter is running. When using a static TOP value there are practically no differences between the
two modes of operation.
In phase correct PWM mode, the compare units allow generation of PWM waveforms on the OC1x pins. Setting the
COM1x1:0 bits to two will produce a non-inverted PWM and an inverted PWM output can be generated by setting the
COM1x1:0 to three. The actual OC1x value will only be visible on the port pin if the data direction for the port pin is set as
output (DDR_OC1x). The PWM waveform is generated by setting (or clearing) the OC1x register at the compare match
between OCR1x and TCNT1 when the counter increments, and clearing (or setting) the OC1x register at compare match
between OCR1x and TCNT1 when the counter decrements.
The PWM frequency for the output when using phase correct PWM can be calculated by the following equation:
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCR1x register represent special cases when generating a PWM waveform output in the phase
correct PWM mode. If the OCR1x is set equal to BOTTOM the output will be continuously low and if set equal to TOP the
output will be continuously high for non-inverted PWM mode. For inverted PWM the output will have the opposite logic
values. If OCR1A is used to define the TOP value (WGM13:0 = 11) and COM1A1:0 = 1, the OC1A output will toggle with a
50% duty cycle.
5.14.8.5 Phase and Frequency Correct PWM Mode
The phase and frequency correct pulse width modulation, or phase and frequency correct PWM mode (WGM13:0 = 8 or 9)
provides a high resolution phase and frequency correct PWM waveform generation option. The phase and frequency correct
PWM mode is, like the phase correct PWM mode, based on a dual-slope operation. The counter counts repeatedly from
BOTTOM (0x0000) to TOP and then from TOP to BOTTOM. In non-inverting compare output mode, the output compare
(OC1x) is cleared on the compare match between TCNT1 and OCR1x while upcounting, and set on the compare match
while downcounting. In inverting compare output mode, the operation is inverted. The dual-slope operation gives a lower
maximum operation frequency compared to the single-slope operation. However, due to the symmetric feature of the
dual-slope PWM modes, these modes are preferred for motor control applications.
The main difference between the phase correct, and the phase and frequency correct PWM mode is the time the OCR1x
register is updated by the OCR1x buffer register (see Figure 5-47 on page 127 and Figure 5-48 on page 129).
The PWM resolution for the phase and frequency correct PWM mode can be defined by either ICR1 or OCR1A. The
minimum resolution allowed is 2-bit (ICR1 or OCR1A set to 0x0003), and the maximum resolution is 16-bit (ICR1 or OCR1A
set to MAX). The PWM resolution in bits can be calculated using the following equation:
fOCnxPCPWM
fclk_I/O
2NTOP××
-------------------------------
=
RPFCPWM
log TOP 1+()
log 2()
---------------------------------
=
129
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In phase and frequency correct PWM mode the counter is incremented until the counter value matches either the value in
ICR1 (WGM13:0 = 8), or the value in OCR1A (WGM13:0 = 9). The counter has then reached the TOP and changes the
count direction. The TCNT1 value will be equal to TOP for one timer clock cycle. The timing diagram for the phase correct
and frequency correct PWM mode is shown on Figure 5-48. The figure shows phase and frequency correct PWM mode
when OCR1A or ICR1 is used to define TOP. The TCNT1 value is in the timing diagram shown as a histogram for illustrating
the dual-slope operation. The diagram includes non-inverted and inverted PWM outputs. The small horizontal line marks on
the TCNT1 slopes represent compare matches between OCR1x and TCNT1. The OC1x interrupt flag will be set when a
compare match occurs.
Figure 5-48. Phase and Frequency Correct PWM Mode, Timing Diagram
The Timer/Counter overflow flag (TOV1) is set at the same timer clock cycle as the OCR1x registers are updated with the
double buffer value (at BOTTOM). When either OCR1A or ICR1 is used for defining the TOP value, the OC1A or ICF1 flag
set when TCNT1 has reached TOP. The interrupt flags can then be used to generate an interrupt each time the counter
reaches the TOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is higher or equal to the value of all of the
compare registers. If the TOP value is lower than any of the compare registers, a compare match will never occur between
the TCNT1 and the OCR1x.
As Figure 5-48 shows the output generated is, in contrast to the phase correct mode, symmetrical in all periods. Since the
OCR1x registers are updated at BOTTOM, the length of the rising and the falling slopes will always be equal. This gives
symmetrical output pulses and is therefore frequency correct.
Using the ICR1 register for defining TOP works well when using fixed TOP values. By using ICR1, the OCR1A register is
free to be used for generating a PWM output on OC1A. However, if the base PWM frequency is actively changed by
changing the TOP value, using the OCR1A as TOP is clearly a better choice due to its double buffer feature.
In phase and frequency correct PWM mode, the compare units allow generation of PWM waveforms on the OC1x pins.
Setting the COM1x1:0 bits to two will produce a non-inverted PWM and an inverted PWM output can be generated by setting
the COM1x1:0 to three (see Table 5-55 on page 133). The actual OC1x value will only be visible on the port pin if the data
direction for the port pin is set as output (DDR_OC1x). The PWM waveform is generated by setting (or clearing) the OC1x
register at the compare match between OCR1x and TCNT1 when the counter increments, and clearing (or setting) the OC1x
register at compare match between OCR1x and TCNT1 when the counter decrements. The PWM frequency for the output
when using phase and frequency correct PWM can be calculated by the following equation:
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
1234
TCNTn
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCnx
OCnx
Period
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
OCRnx/ TOP Update and
TOVn Interrupt Flag Set
(Interrupt on Bottom)
fOCnxPFCPWM
fclk_I/O
2N×TOP×
-------------------------------
=
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130
The extreme values for the OCR1x register represents special cases when generating a PWM waveform output in the phase
correct PWM mode. If the OCR1x is set equal to BOTTOM the output will be continuously low and if set equal to TOP the
output will be set to high for non-inverted PWM mode. For inverted PWM the output will have the opposite logic values. If
OCR1A is used to define the TOP value (WGM13:0 = 9) and COM1A1:0 = 1, the OC1A output will toggle with a 50% duty
cycle.
5.14.9 Timer/Counter Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkT1) is therefore shown as a clock enable signal in the
following figures. The figures include information on when interrupt flags are set, and when the OCR1x register is updated
with the OCR1x buffer value (only for modes utilizing double buffering). Figure 5-49 shows a timing diagram for the setting of
OCF1x.
Figure 5-49. Timer/Counter Timing Diagram, Setting of OCF1x, no Prescaling
Figure 5-50 shows the same timing data, but with the prescaler enabled.
Figure 5-50. Timer/Counter Timing Diagram, Setting of OCF1x, with Prescaler (fclk_I/O/8)
OCRnx - 1
clkI/O
(clkI/O/1)
TCNTn
OCRnx
OCFnx
clkTn
OCRnx
OCRnx Value
OCRnx + 1 OCRnx + 2
OCRnx - 1
clkI/O
(clkI/O/8)
TCNTn
OCRnx
OCFnx
clkTn
OCRnx OCRnx + 1
OCRnx Value
OCRnx + 2
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Figure 5-51 shows the count sequence close to TOP in various modes. When using phase and frequency correct PWM
mode the OCR1x register is updated at BOTTOM. The timing diagrams will be the same, but TOP should be replaced by
BOTTOM, TOP-1 by BOTTOM+1 and so on. The same renaming applies for modes that set the TOV1 flag at BOTTOM.
Figure 5-51. Timer/Counter Timing Diagram, no Prescaling
Figure 5-52 shows the same timing data, but with the prescaler enabled.
Figure 5-52. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
TOP - 1
clkI/O
(clkI/O/1)
TCNTn
(CTC and FPWM)
OCRnx
(Update at TOP)
TCNTn
(PC and PFC PWM)
TOVn (FPWM)
and ICFn
(if used as TOP)
clkTn
TOP
Old OCRnx Value New OCRnx Value
BOTTOM BOTTOM + 1
TOP - 1 TOP TOP - 1 TOP - 2
TOP - 1 TOP BOTTOM BOTTOM + 1
TOP - 1 TOP TOP - 1 TOP - 2
clkI/O
(clkI/O/8)
TCNTn
(CTC and FPWM)
OCRnx
(Update at TOP)
TCNTn
(PC and PFC PWM)
TOVn (FPWM)
and ICFn
(if used as TOP)
clkTn
Old OCRnx Value New OCRnx Value
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5.14.10 16-bit Timer/Counter Register Description
5.14.10.1 Timer/Counter1 Control Register A – TCCR1A
• Bit 7:6 – COM1A1:0: Compare Output Mode for Channel A
• Bit 5:4 – COM1B1:0: Compare Output Mode for Channel B
The COM1A1:0 and COM1B1:0 control the output compare pins (OC1A and OC1B respectively) behavior. If one or both of
the COM1A1:0 bits are written to one, the OC1A output overrides the normal port functionality of the I/O pin it is connected
to. If one or both of the COM1B1:0 bit are written to one, the OC1B output overrides the normal port functionality of the I/O
pin it is connected to. However, note that the data direction register (DDR) bit corresponding to the OC1A or OC1B pin must
be set in order to enable the output driver.
When the OC1A or OC1B is connected to the pin, the function of the COM1x1:0 bits is dependent of the WGM13:0 bits
setting. Table 5-53 shows the COM1x1:0 bit functionality when the WGM13:0 bits are set to a Normal or a CTC mode
(non-PWM).
Table 5-54 shows the COM1x1:0 bit functionality when the WGM13:0 bits are set to the fast PWM mode.
Bit 76543210
COM1A1 COM1A0 COM1B1 COM1B0 – – WGM11 WGM10 TCCR1A
Read/Write R/W R/W R/W R/W R R R/W R/W
Initial Value00000000
Table 5-53. Compare Output Mode, non-PWM
COM1A1/COM1B1 COM1A0/COM1B0 Description
0 0 Normal port operation, OC1A/OC1B disconnected.
0 1 Toggle OC1A/OC1B on compare match.
1 0 Clear OC1A/OC1B on compare match (set output to low level).
1 1 Set OC1A/OC1B on compare match (set output to high level).
Table 5-54. Compare Output Mode, Fast PWM(1)
COM1A1/COM1B1 COM1A0/COM1B0 Description
0 0 Normal port operation, OC1A/OC1B disconnected.
0 1
WGM13:0 = 14 or 15: Toggle OC1A on compare match, OC1B
disconnected (normal port operation). For all other WGM1 settings,
normal port operation, OC1A/OC1B disconnected.
1 0 Clear OC1A/OC1B on compare match, set OC1A/OC1B at TOP
1 1 Set OC1A/OC1B on compare match, clear OC1A/OC1B at TOP
Note: 1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is set. In this case the
compare match is ignored, but the set or clear is done at TOP. See Section 5.14.8.3 “Fast PWM Mode” on
page 125 for more details.
133
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Table 5-55 shows the COM1x1:0 bit functionality when the WGM13:0 bits are set to the phase correct or the phase and
frequency correct, PWM mode.
• Bit 1:0 – WGM11:0: Waveform Generation Mode
Combined with the WGM13:2 bits found in the TCCR1B register, these bits control the counting sequence of the counter, the
source for maximum (TOP) counter value, and what type of waveform generation to be used (see Table 5-56 on page 133).
Modes of operation supported by the Timer/Counter unit are: Normal mode (counter), clear timer on compare match (CTC)
mode, and three types of pulse width modulation (PWM) modes (see Section 5.14.8 “Modes of Operation” on page 124).
Table 5-55. Compare Output Mode, Phase Correct and Phase and Frequency Correct PWM(1)
COM1A1/COM1B1 COM1A0/COM1B0 Description
0 0 Normal port operation, OC1A/OC1B disconnected.
0 1
WGM13:0 = 8, 9, 10 or 11: Toggle OC1A on compare match, OC1B
disconnected (normal port operation). For all other WGM1 settings,
normal port operation, OC1A/OC1B disconnected.
1 0 Clear OC1A/OC1B on compare match when up-counting. Set
OC1A/OC1B on compare match when downcounting.
1 1 Set OC1A/OC1B on compare match when up-counting. Clear
OC1A/OC1B on compare match when downcounting.
Note: 1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is set. See Section 5.14.8.4
“Phase Correct PWM Mode” on page 127 for more details.
Table 5-56. Waveform Generation Mode Bit Description(1)
Mode WGM13
WGM12
(CTC1)
WGM11
(PWM11)
WGM10
(PWM10)
Timer/Counter Mode of
Operation TOP
Update of
OCR1x at
TOV1 Flag
Set on
00000Normal 0xFFFF Immediate MAX
10001PWM, phase correct, 8-bit 0x00FF TOP BOTTOM
20010PWM, phase correct, 9-bit 0x01FF TOP BOTTOM
30011PWM, phase correct, 10-bit 0x03FF TOP BOTTOM
40100CTC OCR1A Immediate MAX
50101Fast PWM, 8-bit 0x00FF TOP TOP
60110Fast PWM, 9-bit 0x01FF TOP TOP
70111Fast PWM, 10-bit 0x03FF TOP TOP
81000PWM, phase and frequency
correct ICR1 BOTTOM BOTTOM
91001PWM, phase and frequency
correct OCR1A BOTTOM BOTTOM
10 1010PWM, phase correct ICR1 TOP BOTTOM
11 1011PWM, phase correct OCR1A TOP BOTTOM
12 1100CTC ICR1 Immediate MAX
13 1101(Reserved) – – –
14 1110Fast PWM ICR1 TOP TOP
15 1111Fast PWM OCR1A TOP TOP
Note: 1. The CTC1 and PWM11:0 bit definition names are obsolete. Use the WGM12:0 definitions. However, the
functionality and location of these bits are compatible with previous versions of the timer.
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5.14.10.2 Timer/Counter1 Control Register B – TCCR1B
• Bit 7 – ICNC1: Input Capture Noise Canceler
Setting this bit (to one) activates the input capture noise canceler. When the noise canceler is activated, the input from the
input capture pin (ICP1) is filtered. The filter function requires four successive equal valued samples of the ICP1 pin for
changing its output. The input capture is therefore delayed by four oscillator cycles when the noise canceler is enabled.
• Bit 6 – ICES1: Input Capture Edge Select
This bit selects which edge on the Input Capture pin (ICP1) that is used to trigger a capture event. When the ICES1 bit is
written to zero, a falling (negative) edge is used as trigger, and when the ICES1 bit is written to one, a rising (positive) edge
will trigger the capture.
When a capture is triggered according to the ICES1 setting, the counter value is copied into the input capture register
(ICR1). The event will also set the input capture flag (ICF1), and this can be used to cause an input capture interrupt, if this
interrupt is enabled.
When the ICR1 is used as TOP value (see description of the WGM13:0 bits located in the TCCR1A and the TCCR1B
register), the ICP1 is disconnected and consequently the input capture function is disabled.
• Bit 5 – Reserved Bit
This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be written to zero when
TCCR1B is written.
• Bit 4:3 – WGM13:2: Waveform Generation Mode
See TCCR1A register description.
• Bit 2:0 – CS12:0: Clock Select
The three clock select bits select the clock source to be used by the Timer/Counter, see Figure 5-49 on page 130 and
Figure 5-50 on page 130.
If external pin modes are used for the Timer/Counter1, transitions on the T1 pin will clock the counter even if the pin is
configured as an output. This feature allows software control of the counting.
Bit 7654 3210
ICNC1 ICES1 – WGM13 WGM12 CS12 CS11 CS10 TCCR1B
Read/Write R/W R/W R R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 5-57. Clock Select Bit Description
CS12 CS11 CS10 Description
000No clock source (Timer/Counter stopped).
001clkI/O/1 (no prescaling)
010clkI/O/8 (from prescaler)
011clkI/O/64 (from prescaler)
100clkI/O/256 (from prescaler)
101clkI/O/1024 (from prescaler)
110External clock source on T1 pin. Clock on falling edge.
111External clock source on T1 pin. Clock on rising edge.
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5.14.10.3 Timer/Counter1 Control Register C – TCCR1C
• Bit 7 – FOC1A: Force Output Compare for Channel A
• Bit 6 – FOC1B: Force Output Compare for Channel B
The FOC1A/FOC1B bits are only active when the WGM13:0 bits specifies a non-PWM mode. However, for ensuring
compatibility with future devices, these bits must be set to zero when TCCR1A is written when operating in a PWM mode.
When writing a logical one to the FOC1A/FOC1B bit, an immediate compare match is forced on the Waveform Generation
unit. The OC1A/OC1B output is changed according to its COM1x1:0 bits setting. Note that the FOC1A/FOC1B bits are
implemented as strobes. Therefore it is the value present in the COM1x1:0 bits that determine the effect of the forced
compare.
A FOC1A/FOC1B strobe will not generate any interrupt nor will it clear the timer in clear timer on compare match (CTC)
mode using OCR1A as TOP.
The FOC1A/FOC1B bits are always read as zero.
5.14.10.4 Timer/Counter1 – TCNT1H and TCNT1L
The two Timer/Counter I/O locations (TCNT1H and TCNT1L, combined TCNT1) give direct access, both for read and for
write operations, to the Timer/Counter unit 16-bit counter. To ensure that both the high and low bytes are read and written
simultaneously when the CPU accesses these registers, the access is performed using an 8-bit temporary high byte register
(TEMP). This temporary register is shared by all the other 16-bit registers see
Section 5.14.2 “Accessing 16-bit Registers” on page 115.
Modifying the counter (TCNT1) while the counter is running introduces a risk of missing a compare match between TCNT1
and one of the OCR1x registers.
Writing to the TCNT1 register blocks (removes) the compare match on the following timer clock for all compare units.
5.14.10.5 Output Compare Register 1 A – OCR1AH and OCR1AL
5.14.10.6 Output Compare Register 1 B – OCR1BH and OCR1BL
Bit 7654 3210
FOC1A FOC1B – – – – – – TCCR1C
Read/Write R/W R/W R R R R R R
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
TCNT1[15:8] TCNT1H
TCNT1[7:0] TCNT1L
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
OCR1A[15:8] OCR1AH
OCR1A[7:0] OCR1AL
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
OCR1B[15:8] OCR1BH
OCR1B[7:0] OCR1BL
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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The output compare registers contain a 16-bit value that is continuously compared with the counter value (TCNT1). A match
can be used to generate an output compare interrupt, or to generate a waveform output on the OC1x pin.
The output compare registers are 16-bit in size. To ensure that both the high and low bytes are written simultaneously when
the CPU writes to these registers, the access is performed using an 8-bit temporary high byte register (TEMP). This
temporary register is shared by all the other 16-bit registers (see Section 5.14.2 “Accessing 16-bit Registers” on page 115).
5.14.10.7 Input Capture Register 1 – ICR1H and ICR1L
The input capture is updated with the counter (TCNT1) value each time an event occurs on the ICP1 pin (or optionally on the
analog comparator output for Timer/Counter1). The input capture can be used for defining the counter TOP value.
The input capture register is 16-bit in size. To ensure that both the high and low bytes are read simultaneously when the
CPU accesses these registers, the access is performed using an 8-bit temporary high byte register (TEMP). This temporary
register is shared by all the other 16-bit registers (see Section 5.14.2 “Accessing 16-bit Registers” on page 115).
5.14.10.8 Timer/Counter1 Interrupt Mask Register – TIMSK1
• Bit 7, 6 – Res: Reserved Bits
These bits are unused bits in the Atmel® ATA6612C/ATA6613C, and will always read as zero.
• Bit 5 – ICIE1: Timer/Counter1, Input Capture Interrupt Enable
When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the Timer/Counter1
input capture interrupt is enabled. The corresponding interrupt vector (see Section 5.9 “Interrupts” on page 70) is executed
when the ICF1 flag, located in TIFR1, is set.
• Bit 4, 3 – Res: Reserved Bits
These bits are unused bits in the Atmel ATA6612C/ATA6613C, and will always read as zero.
• Bit 2 – OCIE1B: Timer/Counter1, Output Compare B Match Interrupt Enable
When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the Timer/Counter1
output compare B match interrupt is enabled. The corresponding interrupt vector (see Section 5.9 “Interrupts” on page 70) is
executed when the OCF1B flag, located in TIFR1, is set.
• Bit 1 – OCIE1A: Timer/Counter1, Output Compare A Match Interrupt Enable
When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the Timer/Counter1
output compare A match interrupt is enabled. The corresponding interrupt vector (see Section 5.9 “Interrupts” on page 70) is
executed when the OCF1A flag, located in TIFR1, is set.
• Bit 0 – TOIE1: Timer/Counter1, Overflow Interrupt Enable
When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the Timer/Counter1
overflow interrupt is enabled. The corresponding interrupt vector (see Section 5.8.9 “Watchdog Timer” on page 66) is
executed when the TOV1 flag, located in TIFR1, is set.
Bit 76543210
ICR1[15:8] ICR1H
ICR1[7:0] ICR1L
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
– – ICIE1 – – OCIE1B OCIE1A TOIE1 TIMSK1
Read/Write R R R/W R R R/W R/W R/W
Initial Value00000000
137
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5.14.10.9 Timer/Counter1 Interrupt Flag Register – TIFR1
• Bit 7, 6 – Res: Reserved Bits
These bits are unused bits in the Atmel® ATA6612C/ATA6613C, and will always read as zero.
• Bit 5 – ICF1: Timer/Counter1, Input Capture Flag
This flag is set when a capture event occurs on the ICP1 pin. When the input capture register (ICR1) is set by the WGM13:0
to be used as the TOP value, the ICF1 flag is set when the counter reaches the TOP value.
ICF1 is automatically cleared when the input capture interrupt vector is executed. Alternatively, ICF1 can be cleared by
writing a logic one to its bit location.
• Bit 4, 3 – Res: Reserved Bits
These bits are unused bits in the Atmel ATA6612C/ATA6613C, and will always read as zero.
• Bit 2 – OCF1B: Timer/Counter1, Output Compare B Match Flag
This flag is set in the timer clock cycle after the counter (TCNT1) value matches the output compare register B (OCR1B).
Note that a forced output compare (FOC1B) strobe will not set the OCF1B flag.
OCF1B is automatically cleared when the output compare match B interrupt vector is executed. Alternatively, OCF1B can be
cleared by writing a logic one to its bit location.
• Bit 1 – OCF1A: Timer/Counter1, Output Compare A Match Flag
This flag is set in the timer clock cycle after the counter (TCNT1) value matches the output compare register A (OCR1A).
Note that a forced output compare (FOC1A) strobe will not set the OCF1A flag.
OCF1A is automatically cleared when the output compare match A interrupt vector is executed. Alternatively, OCF1A can be
cleared by writing a logic one to its bit location.
• Bit 0 – TOV1: Timer/Counter1, Overflow Flag
The setting of this flag is dependent of the WGM13:0 bits setting. In normal and CTC modes, the TOV1 flag is set when the
timer overflows. Refer to Table 5-56 on page 133 for the TOV1 flag behavior when using another WGM13:0 bit setting.
TOV1 is automatically cleared when the Timer/Counter1 overflow interrupt vector is executed. Alternatively, TOV1 can be
cleared by writing a logic one to its bit location.
5.15 8-bit Timer/Counter2 with PWM and Asynchronous Operation
Timer/Counter2 is a general purpose, single channel, 8-bit Timer/Counter module. The main features are:
●Single channel counter
●Clear timer on compare match (auto reload)
●Glitch-free, phase correct pulse width modulator (PWM)
●Frequency generator
●10-bit clock prescaler
●Overflow and compare match interrupt sources (TOV2, OCF2A and OCF2B)
●Allows clocking from external 32kHz watch crystal independent of the I/O clock
Bit 76543210
––ICF1––OCF1BOCF1ATOV1TIFR1
Read/Write R R R/W R R R/W R/W R/W
Initial Value00000000
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5.15.1 Overview
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 5-53. The device-specific I/O register and bit
locations are listed in the Section 5.15.8 “8-bit Timer/Counter Register Description” on page 148.
The PRTIM2 bit in Section 5.7.7.1 “Power Reduction Register - PRR” on page 58 must be written to zero to enable
Timer/Counter2 module.
Figure 5-53. 8-bit Timer/Counter Block Diagram
TCNTn
Timer/Counter
Count
Clear
Direction
OCRnA
OCRnB
TCCRnA TCCRnB
=
TOP BOTTOM
OCnA (Int. Req.)
Waveform
Generation
Fixed
TOP
Value
DATA BUS
=
== 0
OCnA
OCnB (Int. Req.)
Waveform
Generation OCnB
Control Logic clkTn
clkI/O
Prescaler
TOVn (Int. Req.)
T/C
Oscillator
TOSC1
TOSC2
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5.15.1.1 Registers
The Timer/Counter (TCNT2) and output compare register (OCR2A and OCR2B) are 8-bit registers. Interrupt request
(shorten as Int.Req.) signals are all visible in the timer interrupt flag register (TIFR2). All interrupts are individually masked
with the timer interrupt mask register (TIMSK2). TIFR2 and TIMSK2 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or asynchronously clocked from the TOSC1/2 pins, as
detailed later in this section. The asynchronous operation is controlled by the asynchronous status register (ASSR). The
clock select logic block controls which clock source he Timer/Counter uses to increment (or decrement) its value. The
Timer/Counter is inactive when no clock source is selected. The output from the clock select logic is referred to as the timer
clock (clkT2).
The double buffered output compare register (OCR2A and OCR2B) are compared with the Timer/Counter value at all times.
The result of the compare can be used by the waveform generator to generate a PWM or variable frequency output on the
output compare pins (OC2A and OC2B). See Section 5.15.4 “Output Compare Unit” on page 140 for details. The compare
match event will also set the compare flag (OCF2A or OCF2B) which can be used to generate an output compare interrupt
request.
5.15.1.2 Definitions
Many register and bit references in this document are written in general form. A lower case “n” replaces the Timer/Counter
number, in this case 2. However, when using the register or bit defines in a program, the precise form must be used, i.e.,
TCNT2 for accessing Timer/Counter2 counter value and so on.
The definitions below are also used extensively throughout the section.
5.15.2 Timer/Counter Clock Sources
The Timer/Counter can be clocked by an internal synchronous or an external asynchronous clock source. The clock source
clkT2 is by default equal to the MCU clock, clkI/O. When the AS2 bit in the ASSR register is written to logic one, the clock
source is taken from the Timer/Counter oscillator connected to TOSC1 and TOSC2. For details on asynchronous operation
(see Section 5.15.9.2 “Asynchronous Status Register – ASSR” on page 154). For details on clock sources and prescaler,
see Section 5.15.10 “Timer/Counter Prescaler” on page 155.
5.15.3 Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure 5-54 shows a block diagram
of the counter and its surrounding environment.
Figure 5-54. Counter Unit Block Diagram
Table 5-58. Definitions
Parameter Definition
BOTTOM The counter reaches the BOTTOM when it becomes zero (0x00).
MAX The counter reaches its MAXimum when it becomes 0xFF (decimal 255).
TOP
The counter reaches the TOP when it becomes equal to the highest value in the count sequence. The
TOP value can be assigned to be the fixed value 0xFF (MAX) or the value stored in the OCR2A register.
The assignment is dependent on the mode of operation.
TopBottom
TOVn
(Int. Req.)
DATA BUS
Control Logic
TCNTn
clkTn
Clear
Count
Direction
clkI/O
Prescaler
T/C
Oscillator
TOSC1
TOSC2
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Signal description (internal signals):
count Increment or decrement TCNT2 by 1.
direction Selects between increment and decrement.
clear Clear TCNT2 (set all bits to zero).
clkTn Timer/Counter clock, referred to as clkT2 in the following.
top Signalizes that TCNT2 has reached maximum value.
bottom Signalizes that TCNT2 has reached minimum value (zero).
Depending on the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clkT2).
clkT2 can be generated from an external or internal clock source, selected by the clock select bits (CS22:0). When no clock
source is selected (CS22:0 = 0) the timer is stopped. However, the TCNT2 value can be accessed by the CPU, regardless of
whether clkT2 is present or not. A CPU write overrides (has priority over) all counter clear or count operations.
The counting sequence is determined by the setting of the WGM21 and WGM20 bits located in the Timer/Counter control
register (TCCR2A) and the WGM22 located in the Timer/Counter control register B (TCCR2B). There are close connections
between how the counter behaves (counts) and how waveforms are generated on the output compare outputs OC2A and
OC2B. For more details about advanced counting sequences and waveform generation (see Section 5.15.6 “Modes of
Operation” on page 142).
The Timer/Counter overflow flag (TOV2) is set according to the mode of operation selected by the WGM22:0 bits. TOV2 can
be used for generating a CPU interrupt.
5.15.4 Output Compare Unit
The 8-bit comparator continuously compares TCNT2 with the output compare register (OCR2A and OCR2B). Whenever
TCNT2 equals OCR2A or OCR2B, the comparator signals a match. A match will set the output compare flag (OCF2A or
OCF2B) at the next timer clock cycle. If the corresponding interrupt is enabled, the output compare flag generates an output
compare interrupt. The output compare flag is automatically cleared when the interrupt is executed. Alternatively, the output
compare flag can be cleared by software by writing a logical one to its I/O bit location. The waveform generator uses the
match signal to generate an output according to operating mode set by the WGM22:0 bits and compare output mode
(COM2x1:0) bits. The max and bottom signals are used by the waveform generator for handling the special cases of the
extreme values in some modes of operation (see Section 5.15.6 “Modes of Operation” on page 142).
Figure 5-55 shows a block diagram of the output compare unit.
Figure 5-55. Output Compare Unit, Block Diagram
OCFnx (Int. Req.)
= (8-bit Comparator)
OCRnx
Waveform Generator
TCNTn
OCnx
Top
Bottom
FOCn
WGMn1:0 COMnX1:0
DATA BUS
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The OCR2x register is double buffered when using any of the pulse width modulation (PWM) modes. For the normal and
clear timer on compare (CTC) modes of operation, the double buffering is disabled. The double buffering synchronizes the
update of the OCR2x compare register to either top or bottom of the counting sequence. The synchronization prevents the
occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
The OCR2x register access may seem complex, but this is not case. When the double buffering is enabled, the CPU has
access to the OCR2x buffer register, and if double buffering is disabled the CPU will access the OCR2x directly.
5.15.4.1 Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced by writing a one to the force
output compare (FOC2x) bit. Forcing compare match will not set the OCF2x flag or reload/clear the timer, but the OC2x pin
will be updated as if a real compare match had occurred (the COM2x1:0 bits settings define whether the OC2x pin is set,
cleared or toggled).
5.15.4.2 Compare Match Blocking by TCNT2 Write
All CPU write operations to the TCNT2 register will block any compare match that occurs in the next timer clock cycle, even
when the timer is stopped. This feature allows OCR2x to be initialized to the same value as TCNT2 without triggering an
interrupt when the Timer/Counter clock is enabled.
5.15.4.3 Using the Output Compare Unit
Since writing TCNT2 in any mode of operation will block all compare matches for one timer clock cycle, there are risks
involved when changing TCNT2 when using the output compare channel, independently of whether the Timer/Counter is
running or not. If the value written to TCNT2 equals the OCR2x value, the compare match will be missed, resulting in
incorrect waveform generation. Similarly, do not write the TCNT2 value equal to BOTTOM when the counter is
downcounting.
The setup of the OC2x should be performed before setting the data direction register for the port pin to output. The easiest
way of setting the OC2x value is to use the force output compare (FOC2x) strobe bit in normal mode. The OC2x register
keeps its value even when changing between waveform generation modes.
Be aware that the COM2x1:0 bits are not double buffered together with the compare value. Changing the COM2x1:0 bits will
take effect immediately.
5.15.5 Compare Match Output Unit
The compare output mode (COM2x1:0) bits have two functions. The waveform generator uses the COM2x1:0 bits for
defining the output compare (OC2x) state at the next compare match. Also, the COM2x1:0 bits control the OC2x pin output
source. Figure 5-56 on page 142 shows a simplified schematic of the logic affected by the COM2x1:0 bit setting. The I/O
registers, I/O bits, and I/O pins in the figure are shown in bold. Only the parts of the general I/O port control registers (DDR
and PORT) that are affected by the COM2x1:0 bits are shown. When referring to the OC2x state, the reference is for the
internal OC2x register, not the OC2x pin.
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Figure 5-56. Compare Match Output Unit, Schematic
The general I/O port function is overridden by the output compare (OC2x) from the waveform generator if either of the
COM2x1:0 bits are set. However, the OC2x pin direction (input or output) is still controlled by the data direction register
(DDR) for the port pin. The data direction register bit for the OC2x pin (DDR_OC2x) must be set as output before the OC2x
value is visible on the pin. The port override function is independent of the waveform generation mode.
The design of the output compare pin logic allows initialization of the OC2x state before the output is enabled. Note that
some COM2x1:0 bit settings are reserved for certain modes of operation (see Section 5.15.8 “8-bit Timer/Counter Register
Description” on page 148).
5.15.5.1 Compare Output Mode and Waveform Generation
The waveform generator uses the COM2x1:0 bits differently in normal, CTC, and PWM modes. For all modes, setting the
COM2x1:0 = 0 tells the waveform generator that no action on the OC2x register is to be performed on the next compare
match. For compare output actions in the non-PWM modes refer to Table 5-62 on page 149. For fast PWM mode, refer to
Table 5-63 on page 149, and for phase correct PWM refer to Table 5-64 on page 149.
A change of the COM2x1:0 bits state will have effect at the first compare match after the bits are written. For non-PWM
modes, the action can be forced to have immediate effect by using the FOC2x strobe bits.
5.15.6 Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the output compare pins, is defined by the combination of
the waveform generation mode (WGM22:0) and compare output mode (COM2x1:0) bits. The compare output mode bits do
not affect the counting sequence, while the waveform generation mode bits do. The COM2x1:0 bits control whether the
PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes the COM2x1:0 bits
control whether the output should be set, cleared, or toggled at a compare match (see Section 5.15.5 “Compare Match
Output Unit” on page 141).
For detailed timing information refer to Section 5.15.7 “Timer/Counter Timing Diagrams” on page 146.
DATA BUS
0
1
QD
COMnx1
COMnx0
FOCnx
OCnx
Waveform
Generator
QD
PORT
QD
DDR
OCnx
Pin
clkI/O
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5.15.6.1 Normal Mode
The simplest mode of operation is the normal mode (WGM22:0 = 0). In this mode the counting direction is always up
(incrementing), and no counter clear is performed. The counter simply overruns when it passes its maximum 8-bit value
(TOP = 0xFF) and then restarts from the bottom (0x00). In normal operation the Timer/Counter overflow flag (TOV2) will be
set in the same timer clock cycle as the TCNT2 becomes zero. The TOV2 flag in this case behaves like a ninth bit, except
that it is only set, not cleared. However, combined with the timer overflow interrupt that automatically clears the TOV2 flag,
the timer resolution can be increased by software. There are no special cases to consider in the normal mode, a new counter
value can be written anytime.
The output compare unit can be used to generate interrupts at some given time. Using the output compare to generate
waveforms in normal mode is not recommended, since this will occupy too much of the CPU time.
5.15.6.2 Clear Timer on Compare Match (CTC) Mode
In clear timer on compare or CTC mode (WGM22:0 = 2), the OCR2A register is used to manipulate the counter resolution. In
CTC mode the counter is cleared to zero when the counter value (TCNT2) matches the OCR2A. The OCR2A defines the top
value for the counter, hence also its resolution. This mode allows greater control of the compare match output frequency. It
also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 5-57. The counter value (TCNT2) increases until a compare match
occurs between TCNT2 and OCR2A, and then counter (TCNT2) is cleared.
Figure 5-57. CTC Mode, Timing Diagram
An interrupt can be generated each time the counter value reaches the TOP value by using the OCF2A flag. If the interrupt
is enabled, the interrupt handler routine can be used for updating the TOP value. However, changing TOP to a value close to
BOTTOM when the counter is running with none or a low prescaler value must be done with care since the CTC mode does
not have the double buffering feature. If the new value written to OCR2A is lower than the current value of TCNT2, the
counter will miss the compare match. The counter will then have to count to its maximum value (0xFF) and wrap around
starting at 0x00 before the compare match can occur.
For generating a waveform output in CTC mode, the OC2A output can be set to toggle its logical level on each compare
match by setting the compare output mode bits to toggle mode (COM2A1:0 = 1). The OC2A value will not be visible on the
port pin unless the data direction for the pin is set to output. The waveform generated will have a maximum frequency of
fOC2A = fclk_I/O/2 when OCR2A is set to zero (0x00). The waveform frequency is defined by the following equation:
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
As for the normal mode of operation, the TOV2 flag is set in the same timer clock cycle that the counter counts from MAX to
0x00.
12
TCNTn
(COMnx1:0 = 1)
OCnx
(Toggle)
Period 3
OCnx Interrupt
Flag Set
4
fOCnx
fclk_I/O
2N×1 OCRnx+()×
----------------------------------------------------
=
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5.15.6.3 Fast PWM Mode
The fast pulse width modulation or fast PWM mode (WGM22:0 = 3 or 7) provides a high frequency PWM waveform
generation option. The fast PWM differs from the other PWM option by its single-slope operation. The counter counts from
BOTTOM to TOP then restarts from BOTTOM. TOP is defined as 0xFF when WGM2:0 = 3, and OCR2A when MGM2:0 = 7.
In non-inverting compare output mode, the output compare (OC2x) is cleared on the compare match between TCNT2 and
OCR2x, and set at BOTTOM. In inverting compare output mode, the output is set on compare match and cleared at
BOTTOM. Due to the single-slope operation, the operating frequency of the fast PWM mode can be twice as high as the
phase correct PWM mode that uses dual-slope operation. This high frequency makes the fast PWM mode well suited for
power regulation, rectification, and DAC applications. High frequency allows physically small sized external components
(coils, capacitors), and therefore reduces total system cost.
In fast PWM mode, the counter is incremented until the counter value matches the TOP value. The counter is then cleared at
the following timer clock cycle. The timing diagram for the fast PWM mode is shown in Figure 5-58 on page 144. The TCNT2
value is in the timing diagram shown as a histogram for illustrating the single-slope operation. The diagram includes
non-inverted and inverted PWM outputs. The small horizontal line marks on the TCNT2 slopes represent compare matches
between OCR2x and TCNT2.
Figure 5-58. Fast PWM Mode, Timing Diagram
The Timer/Counter overflow flag (TOV2) is set each time the counter reaches TOP. If the interrupt is enabled, the interrupt
handler routine can be used for updating the compare value.
In fast PWM mode, the compare unit allows generation of PWM waveforms on the OC2x pin. Setting the COM2x1:0 bits to
two will produce a non-inverted PWM and an inverted PWM output can be generated by setting the COM2x1:0 to three. TOP
is defined as 0xFF when WGM2:0 = 3, and OCR2A when MGM2:0 = 7 (see Table 5-60 on page 148). The actual OC2x value
will only be visible on the port pin if the data direction for the port pin is set as output. The PWM waveform is generated by
setting (or clearing) the OC2x register at the compare match between OCR2x and TCNT2, and clearing (or setting) the
OC2x register at the timer clock cycle the counter is cleared (changes from TOP to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
The extreme values for the OCR2A register represent special cases when generating a PWM waveform output in the fast
PWM mode. If the OCR2A is set equal to BOTTOM, the output will be a narrow spike for each MAX+1 timer clock cycle.
Setting the OCR2A equal to MAX will result in a constantly high or low output (depending on the polarity of the output set by
the COM2A1:0 bits.)
1234567
TCNTn
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCn
OCn
Period
OCRnx Update and
TOVn Interrupt Flag Set
OCRnx Interrupt
Flag Set
fOCnxPWM
fclk_I/O
N 256×
-------------------
=
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A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OC2x to toggle its logical
level on each compare match (COM2x1:0 = 1). The waveform generated will have a maximum frequency of foc2 = fclk_I/O/2
when OCR2A is set to zero. This feature is similar to the OC2A toggle in CTC mode, except the double buffer feature of the
output compare unit is enabled in the fast PWM mode.
5.15.6.4 Phase Correct PWM Mode
The phase correct PWM mode (WGM22:0 = 1 or 5) provides a high resolution phase correct PWM waveform generation
option. The phase correct PWM mode is based on a dual-slope operation. The counter counts repeatedly from BOTTOM to
TOP and then from TOP to BOTTOM. TOP is defined as 0xFF when WGM2:0 = 3, and OCR2A when MGM2:0 = 7.
In non-inverting compare output mode, the output compare (OC2x) is cleared on the compare match between TCNT2 and
OCR2x while upcounting, and set on the compare match while downcounting. In inverting output compare mode, the
operation is inverted. The dual-slope operation has lower maximum operation frequency than single slope operation.
However, due to the symmetric feature of the dual-slope PWM modes, these modes are preferred for motor control
applications.
In phase correct PWM mode the counter is incremented until the counter value matches TOP. When the counter reaches
TOP, it changes the count direction. The TCNT2 value will be equal to TOP for one timer clock cycle. The timing diagram for
the phase correct PWM mode is shown on Figure 5-59. The TCNT2 value is in the timing diagram shown as a histogram for
illustrating the dual-slope operation. The diagram includes non-inverted and inverted PWM outputs. The small horizontal line
marks on the TCNT2 slopes represent compare matches between OCR2x and TCNT2.
Figure 5-59. Phase Correct PWM Mode, Timing Diagram
The Timer/Counter overflow flag (TOV2) is set each time the counter reaches BOTTOM. The interrupt flag can be used to
generate an interrupt each time the counter reaches the BOTTOM value.
123
TCNTn
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCn
OCn
Period
TOVn Interrupt
Flag Set
OCRnx Update
OCnx Interrupt
Flag Set
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In phase correct PWM mode, the compare unit allows generation of PWM waveforms on the OC2x pin. Setting the
COM2x1:0 bits to two will produce a non-inverted PWM. An inverted PWM output can be generated by setting the
COM2x1:0 to three. TOP is defined as 0xFF when WGM2:0 = 3, and OCR2A when MGM2:0 = 7
(see Table 5-61 on page 148). The actual OC2x value will only be visible on the port pin if the data direction for the port pin is
set as output. The PWM waveform is generated by clearing (or setting) the OC2x register at the compare match between
OCR2x and TCNT2 when the counter increments, and setting (or clearing) the OC2x register at compare match between
OCR2x and TCNT2 when the counter decrements. The PWM frequency for the output when using phase correct PWM can
be calculated by the following equation:
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
The extreme values for the OCR2A register represent special cases when generating a PWM waveform output in the phase
correct PWM mode. If the OCR2A is set equal to BOTTOM, the output will be continuously low and if set equal to MAX the
output will be continuously high for non-inverted PWM mode. For inverted PWM the output will have the opposite logic
values.
At the very start of period 2 in Figure 5-59 on page 145 OCnx has a transition from high to low even though there is no
compare match. The point of this transition is to guarantee symmetry around BOTTOM. There are two cases that give a
transition without compare match.
●OCR2A changes its value from MAX, like in Figure 5-59 on page 145. When the OCR2A value is MAX the OCn pin
value is the same as the result of a down-counting compare match. To ensure symmetry around BOTTOM the OCn
value at MAX must correspond to the result of an up-counting compare match.
●The timer starts counting from a value higher than the one in OCR2A, and for that reason misses the compare match
and hence the OCn change that would have happened on the way up.
5.15.7 Timer/Counter Timing Diagrams
The following figures show the Timer/Counter in synchronous mode, and the timer clock (clkT2) is therefore shown as a clock
enable signal. In asynchronous mode, clkI/O should be replaced by the Timer/Counter oscillator clock. The figures include
information on when interrupt flags are set. Figure 5-60 contains timing data for basic Timer/Counter operation. The figure
shows the count sequence close to the MAX value in all modes other than phase correct PWM mode.
Figure 5-60. Timer/Counter Timing Diagram, no Prescaling
fOCnxPCPWM
fclk_I/O
N510×
-------------------
=
MAX - 1
clkI/O
(clkI/O/1)
TCNTn
TOVn
clkTn
MAX BOTTOM BOTTOM + 1
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Figure 5-61 shows the same timing data, but with the prescaler enabled.
Figure 5-61. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
Figure 5-62 shows the setting of OCF2A in all modes except CTC mode.
Figure 5-62. Timer/Counter Timing Diagram, Setting of OCF2A, with Prescaler (fclk_I/O/8)
Figure 5-63 shows the setting of OCF2A and the clearing of TCNT2 in CTC mode.
Figure 5-63. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with Prescaler (fclk_I/O/8)
MAX - 1
clkI/O
(clkI/O/8)
TCNTn
TOVn
clkTn
MAX BOTTOM BOTTOM + 1
OCRnx - 1
clkI/O
(clkI/O/8)
TCNTn
OCRnx
OCFnx
clkTn
OCRnx OCRnx + 1
OCRnx Value
OCRnx + 2
TOP - 1
clkI/O
(clkI/O/8)
TCNTn
(CTC)
OCRnx
OCFnx
clkTn
TOP BOTTOM
TOP
BOTTOM + 1
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5.15.8 8-bit Timer/Counter Register Description
5.15.8.1 Timer/Counter Control Register A – TCCR2A
• Bits 7:6 – COM2A1:0: Compare Match Output A Mode
These bits control the output compare pin (OC2A) behavior. If one or both of the COM2A1:0 bits are set, the OC2A output
overrides the normal port functionality of the I/O pin it is connected to. However, note that the data direction register (DDR)
bit corresponding to the OC2A pin must be set in order to enable the output driver.
When OC2A is connected to the pin, the function of the COM2A1:0 bits depends on the WGM22:0 bit setting. Table 5-59
shows the COM2A1:0 bit functionality when the WGM22:0 bits are set to a normal or CTC mode (non-PWM).
Table 5-60 shows the COM2A1:0 bit functionality when the WGM21:0 bits are set to fast PWM mode.
Table 5-61 shows the COM2A1:0 bit functionality when the WGM22:0 bits are set to phase correct PWM mode.
Bit 7 6 5 4 3 2 1 0
COM2A1COM2A0COM2B1COM2B0––WGM21 WGM20 TCCR2A
Read/Write R/W R/W R/W R/W R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 5-59. Compare Output Mode, non-PWM Mode
COM2A1 COM2A0 Description
0 0 Normal port operation, OC0A disconnected.
0 1 Toggle OC2A on compare match
1 0 Clear OC2A on compare match
1 1 Set OC2A on compare match
Table 5-60. Compare Output Mode, Fast PWM Mode(1)
COM2A1 COM2A0 Description
0 0 Normal port operation, OC2A disconnected.
0 1 WGM22 = 0: Normal port operation, OC0A disconnected.
WGM22 = 1: Toggle OC2A on compare match.
1 0 Clear OC2A on compare match, set OC2A at TOP
1 1 Set OC2A on compare match, clear OC2A at TOP
Note: 1. A special case occurs when OCR2A equals TOP and COM2A1 is set. In this case, the compare match is
ignored, but the set or clear is done at TOP. See Section 5.15.6.3 “Fast PWM Mode” on page 144 for more
details.
Table 5-61. Compare Output Mode, Phase Correct PWM Mode()
COM2A1 COM2A0 Description
0 0 Normal port operation, OC2A disconnected.
0 1 WGM22 = 0: Normal port operation, OC2A disconnected.
WGM22 = 1: Toggle OC2A on compare match.
1 0 Clear OC2A on compare match when up-counting. Set OC2A on compare match
when down-counting.
1 1 Set OC2A on compare match when up-counting. Clear OC2A on compare match
when down-counting.
Note: 1. A special case occurs when OCR2A equals TOP and COM2A1 is set. In this case, the compare match is
ignored, but the set or clear is done at TOP. See Section 5.15.6.4 “Phase Correct PWM Mode” on page 145
for more details.
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• Bits 5:4 – COM2B1:0: Compare Match Output B Mode
These bits control the output compare pin (OC2B) behavior. If one or both of the COM2B1:0 bits are set, the OC2B output
overrides the normal port functionality of the I/O pin it is connected to. However, note that the data direction register (DDR)
bit corresponding to the OC2B pin must be set in order to enable the output driver.
When OC2B is connected to the pin, the function of the COM2B1:0 bits depends on the WGM22:0 bit setting. Table 5-62
shows the COM2B1:0 bit functionality when the WGM22:0 bits are set to a normal or CTC mode (non-PWM).
Table 5-63 shows the COM2B1:0 bit functionality when the WGM22:0 bits are set to fast PWM mode.
Table 5-64 shows the COM2B1:0 bit functionality when the WGM22:0 bits are set to phase correct PWM mode.
• Bits 3, 2 – Res: Reserved Bits
These bits are reserved bits in the Atmel® ATA6612C/ATA6613C and will always read as zero.
Table 5-62. Compare Output Mode, non-PWM Mode
COM2B1 COM2B0 Description
0 0 Normal port operation, OC2B disconnected.
0 1 Toggle OC2B on compare match
1 0 Clear OC2B on compare match
1 1 Set OC2B on compare match
Table 5-63. Compare Output Mode, Fast PWM Mode(1)
COM2B1 COM2B0 Description
0 0 Normal port operation, OC2B disconnected.
0 1 Reserved
1 0 Clear OC2B on compare match, set OC2B at TOP
1 1 Set OC2B on compare match, clear OC2B at TOP
Note: 1. A special case occurs when OCR2B equals TOP and COM2B1 is set. In this case, the compare match is
ignored, but the set or clear is done at TOP. See Section 5.15.6.4 “Phase Correct PWM Mode” on page 145
for more details.
Table 5-64. Compare Output Mode, Phase Correct PWM Mode(1)
COM2B1 COM2B0 Description
0 0 Normal port operation, OC2B disconnected.
0 1 Reserved
1 0 Clear OC2B on compare match when up-counting. Set OC2B on compare match
when down-counting.
1 1 Set OC2B on compare match when up-counting. Clear OC2B on compare match
when down-counting.
Note: 1. A special case occurs when OCR2B equals TOP and COM2B1 is set. In this case, the compare match is
ignored, but the set or clear is done at TOP. See Section 5.15.6.4 “Phase Correct PWM Mode” on page 145
for more details.
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• Bits 1:0 – WGM21:0: Waveform Generation Mode
Combined with the WGM22 bit found in the TCCR2B register, these bits control the counting sequence of the counter, the
source for maximum (TOP) counter value, and what type of waveform generation to be used, see Table 5-65. Modes of
operation supported by the Timer/Counter unit are: Normal mode (counter), clear timer on compare match (CTC) mode, and
two types of pulse width modulation (PWM) modes (see Section 5.15.6 “Modes of Operation” on page 142).
5.15.8.2 Timer/Counter Control Register B – TCCR2B
• Bit 7 – FOC2A: Force Output Compare A
The FOC2A bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when TCCR2B is written when operating
in PWM mode. When writing a logical one to the FOC2A bit, an immediate compare match is forced on the waveform
generation unit. The OC2A output is changed according to its COM2A1:0 bits setting. Note that the FOC2A bit is
implemented as a strobe. Therefore it is the value present in the COM2A1:0 bits that determines the effect of the forced
compare.
A FOC2A strobe will not generate any interrupt, nor will it clear the timer in CTC mode using OCR2A as TOP.
The FOC2A bit is always read as zero.
• Bit 6 – FOC2B: Force Output Compare B
The FOC2B bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when TCCR2B is written when operating
in PWM mode. When writing a logical one to the FOC2B bit, an immediate compare match is forced on the waveform
generation unit. The OC2B output is changed according to its COM2B1:0 bits setting. Note that the FOC2B bit is
implemented as a strobe. Therefore it is the value present in the COM2B1:0 bits that determines the effect of the forced
compare.
A FOC2B strobe will not generate any interrupt, nor will it clear the timer in CTC mode using OCR2B as TOP.
The FOC2B bit is always read as zero.
Table 5-65. Waveform Generation Mode Bit Description
Mode WGM2 WGM1 WGM0
Timer/Counter Mode of
Operation TOP
Update of
OCRx at
TOV Flag
Set on(1)(2)
0 0 0 0 Normal 0xFF Immediate MAX
1 0 0 1 PWM, phase correct 0xFF TOP BOTTOM
2 0 1 0 CTC OCRA Immediate MAX
3 0 1 1 Fast PWM 0xFF TOP MAX
4 1 0 0 Reserved – – –
5 1 0 1 PWM, phase correct OCRA TOP BOTTOM
6 1 1 0 Reserved – – –
7 1 1 1 Fast PWM OCRA TOP TOP
Notes: 1. MAX = 0xFF
2. BOTTOM = 0x00
Bit 7 6 5 4 3 2 1 0
FOC2A FOC2B – – WGM22 CS22 CS21 CS20 TCCR2B
Read/Write W W R R R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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• Bits 5:4 – Res: Reserved Bits
These bits are reserved bits in the Atmel® ATA6612C/ATA6613C and will always read as zero.
• Bit 3 – WGM22: Waveform Generation Mode
See the description in Section 5.15.8.1 “Timer/Counter Control Register A – TCCR2A” on page 148.
• Bit 2:0 – CS22:0: Clock Select
The three clock select bits select the clock source to be used by the Timer/Counter (see Table 5-66).
If external pin modes are used for the Timer/Counter0, transitions on the T0 pin will clock the counter even if the pin is
configured as an output. This feature allows software control of the counting.
5.15.8.3 Timer/Counter Register – TCNT2
The Timer/Counter register gives direct access, both for read and write operations, to the Timer/Counter unit 8-bit counter.
Writing to the TCNT2 register blocks (removes) the compare match on the following timer clock. Modifying the counter
(TCNT2) while the counter is running, introduces a risk of missing a compare match between TCNT2 and the OCR2x
registers.
5.15.8.4 Output Compare Register A – OCR2A
The output compare register A contains an 8-bit value that is continuously compared with the counter value (TCNT2). A
match can be used to generate an output compare interrupt, or to generate a waveform output on the OC2A pin.
5.15.8.5 Output Compare Register B – OCR2B
The output compare register B contains an 8-bit value that is continuously compared with the counter value (TCNT2). A
match can be used to generate an output compare interrupt, or to generate a waveform output on the OC2B pin.
Table 5-66. Clock Select Bit Description
CS22 CS21 CS20 Description
0 0 0 No clock source (Timer/Counter stopped).
0 0 1 clkT2S/(no prescaling)
0 1 0 clkT2S/8 (from prescaler)
0 1 1 clkT2S/32 (from prescaler)
1 0 0 clkT2S/64 (from prescaler)
1 0 1 clkT2S/128 (from prescaler)
1 1 0 clkT2S/256 (from prescaler)
1 1 1 clkT2S/1024 (from prescaler)
Bit 76543210
TCNT2[7:0] TCNT2
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
OCR2A[7:0] OCR2A
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
OCR2B[7:0] OCR2B
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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5.15.8.6 Timer/Counter2 Interrupt Mask Register – TIMSK2
• Bit 2 – OCIE2B: Timer/Counter2 Output Compare Match B Interrupt Enable
When the OCIE2B bit is written to one and the I-bit in the status register is set (one), the Timer/Counter2 compare match B
interrupt is enabled. The corresponding interrupt is executed if a compare match in Timer/Counter2 occurs, i.e., when the
OCF2B bit is set in the Timer/Counter 2 interrupt flag register – TIFR2.
• Bit 1 – OCIE2A: Timer/Counter2 Output Compare Match A Interrupt Enable
When the OCIE2A bit is written to one and the I-bit in the status register is set (one), the Timer/Counter2 compare match A
interrupt is enabled. The corresponding interrupt is executed if a compare match in Timer/Counter2 occurs, i.e., when the
OCF2A bit is set in the Timer/Counter 2 interrupt flag register – TIFR2.
• Bit 0 – TOIE2: Timer/Counter2 Overflow Interrupt Enable
When the TOIE2 bit is written to one and the I-bit in the status register is set (one), the Timer/Counter2 overflow interrupt is
enabled. The corresponding interrupt is executed if an overflow in Timer/Counter2 occurs, i.e., when the TOV2 bit is set in
the Timer/Counter2 interrupt flag register – TIFR2.
5.15.8.7 Timer/Counter2 Interrupt Flag Register – TIFR2
• Bit 2 – OCF2B: Output Compare Flag 2 B
The OCF2B bit is set (one) when a compare match occurs between the Timer/Counter2 and the data in OCR2B – Output
compare register2. OCF2B is cleared by hardware when executing the corresponding interrupt handling vector.
Alternatively, OCF2B is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE2B (Timer/Counter2 compare
match interrupt enable), and OCF2B are set (one), the Timer/Counter2 compare match interrupt is executed.
• Bit 1 – OCF2A: Output Compare Flag 2 A
The OCF2A bit is set (one) when a compare match occurs between the Timer/Counter2 and the data in OCR2A – Output
compare register2. OCF2A is cleared by hardware when executing the corresponding interrupt handling vector.
Alternatively, OCF2A is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE2A (Timer/Counter2 compare
match interrupt enable), and OCF2A are set (one), the Timer/Counter2 compare match interrupt is executed.
• Bit 0 – TOV2: Timer/Counter2 Overflow Flag
The TOV2 bit is set (one) when an overflow occurs in Timer/Counter2. TOV2 is cleared by hardware when executing the
corresponding interrupt handling vector. Alternatively, TOV2 is cleared by writing a logic one to the flag. When the
SREG I-bit, TOIE2A (Timer/Counter2 overflow interrupt enable), and TOV2 are set (one), the Timer/Counter2 overflow
interrupt is executed. In PWM mode, this bit is set when Timer/Counter2 changes counting direction at 0x00.
Bit 76543 2 1 0
– – – – – OCIE2B OCIE2A TOIE2 TIMSK2
Read/Write R R R R R R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
–––––OCF2BOCF2ATOV2TIFR2
Read/Write RRRRRR/WR/WR/W
Initial Value00000000
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5.15.9 Asynchronous Operation of the Timer/Counter
5.15.9.1 Asynchronous Operation of Timer/Counter2
When Timer/Counter2 operates asynchronously, some considerations must be taken.
●Warning: When switching between asynchronous and synchronous clocking of Timer/Counter2, the timer registers
TCNT2, OCR2x, and TCCR2x might be corrupted. A safe procedure for switching clock source is:
a. Disable the Timer/Counter2 interrupts by clearing OCIE2x and TOIE2.
b. Select clock source by setting AS2 as appropriate.
c. Write new values to TCNT2, OCR2x, and TCCR2x.
d. To switch to asynchronous operation: Wait for TCN2xUB, OCR2xUB, and TCR2xUB.
e. Clear the Timer/Counter2 interrupt flags.
f. Enable interrupts, if needed.
●The CPU main clock frequency must be more than four times the oscillator frequency.
●When writing to one of the registers TCNT2, OCR2x, or TCCR2x, the value is transferred to a temporary register, and
latched after two positive edges on TOSC1. The user should not write a new value before the contents of the
temporary register have been transferred to its destination. Each of the five mentioned registers have their individual
temporary register, which means that e.g. writing to TCNT2 does not disturb an OCR2x write in progress. To detect
that a transfer to the destination register has taken place, the asynchronous status register – ASSR has been
implemented.
●When entering power-save or ADC noise reduction mode after having written to TCNT2, OCR2x, or TCCR2x, the
user must wait until the written register has been updated if Timer/Counter2 is used to wake up the device. Otherwise,
the MCU will enter sleep mode before the changes are effective. This is particularly important if any of the output
compare2 interrupt is used to wake up the device, since the output compare function is disabled during writing to
OCR2x or TCNT2. If the write cycle is not finished, and the MCU enters sleep mode before the corresponding
OCR2xUB bit returns to zero, the device will never receive a compare match interrupt, and the MCU will not wake up.
●If Timer/Counter2 is used to wake the device up from power-save or ADC noise reduction mode, precautions must be
taken if the user wants to re-enter one of these modes: The interrupt logic needs one TOSC1 cycle to be reset. If the
time between wake-up and re-entering sleep mode is less than one TOSC1 cycle, the interrupt will not occur, and the
device will fail to wake up. If the user is in doubt whether the time before re-entering power-save or ADC noise
reduction mode is sufficient, the following algorithm can be used to ensure that one TOSC1 cycle has elapsed:
a. Write a value to TCCR2x, TCNT2, or OCR2x.
b. Wait until the corresponding update busy flag in ASSR returns to zero.
c. Enter power-save or ADC noise reduction mode.
●When the asynchronous operation is selected, the 32.768kHz oscillator for Timer/Counter2 is always running, except
in power-down and standby modes. After a power-up reset or wake-up from power-down or standby mode, the user
should be aware of the fact that this oscillator might take as long as one second to stabilize. The user is advised to
wait for at least one second before using Timer/Counter2 after power-up or wake-up from power-down or standby
mode. The contents of all Timer/Counter2 registers must be considered lost after a wake-up from power-down or
standby mode due to unstable clock signal upon start-up, no matter whether the oscillator is in use or a clock signal is
applied to the TOSC1 pin.
●Description of wake up from power-save or ADC noise reduction mode when the timer is clocked asynchronously:
When the interrupt condition is met, the wake up process is started on the following cycle of the timer clock, that is,
the timer is always advanced by at least one before the processor can read the counter value. After wake-up, the
MCU is halted for four cycles, it executes the interrupt routine, and resumes execution from the instruction following
SLEEP.
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●Reading of the TCNT2 register shortly after wake-up from power-save may give an incorrect result. Since TCNT2 is
clocked on the asynchronous TOSC clock, reading TCNT2 must be done through a register synchronized to the
internal I/O clock domain. Synchronization takes place for every rising TOSC1 edge. When waking up from
power-save mode, and the I/O clock (clkI/O) again becomes active, TCNT2 will read as the previous value (before
entering sleep) until the next rising TOSC1 edge. The phase of the TOSC clock after waking up from power-save
mode is essentially unpredictable, as it depends on the wake-up time. The recommended procedure for reading
TCNT2 is thus as follows:
a. Write any value to either of the registers OCR2x or TCCR2x.
b. Wait for the corresponding update busy flag to be cleared.
c. Read TCNT2.
During asynchronous operation, the synchronization of the interrupt flags for the asynchronous timer takes 3 processor
cycles plus one timer cycle. The timer is therefore advanced by at least one before the processor can read the timer value
causing the setting of the interrupt flag. The output compare pin is changed on the timer clock and is not synchronized to the
processor clock.
5.15.9.2 Asynchronous Status Register – ASSR
• Bit 6 – EXCLK: Enable External Clock Input
When EXCLK is written to one, and asynchronous clock is selected, the external clock input buffer is enabled and an
external clock can be input on timer oscillator 1 (TOSC1) pin instead of a 32kHz crystal. Writing to EXCLK should be done
before asynchronous operation is selected. Note that the crystal oscillator will only run when this bit is zero.
• Bit 5 – AS2: Asynchronous Timer/Counter2
When AS2 is written to zero, Timer/Counter2 is clocked from the I/O clock, clkI/O. When AS2 is written to one,
Timer/Counter2 is clocked from a crystal oscillator connected to the timer oscillator 1 (TOSC1) pin. When the value of AS2 is
changed, the contents of TCNT2, OCR2A, OCR2B, TCCR2A and TCCR2B might be corrupted.
• Bit 4 – TCN2UB: Timer/Counter2 Update Busy
When Timer/Counter2 operates asynchronously and TCNT2 is written, this bit becomes set. When TCNT2 has been
updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates that TCNT2 is
ready to be updated with a new value.
• Bit 3 – OCR2AUB: Output Compare Register2 Update Busy
When Timer/Counter2 operates asynchronously and OCR2A is written, this bit becomes set. When OCR2A has been
updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates that OCR2A is
ready to be updated with a new value.
• Bit 2 – OCR2BUB: Output Compare Register2 Update Busy
When Timer/Counter2 operates asynchronously and OCR2B is written, this bit becomes set. When OCR2B has been
updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates that OCR2B is
ready to be updated with a new value.
• Bit 1 – TCR2AUB: Timer/Counter Control Register2 Update Busy
When Timer/Counter2 operates asynchronously and TCCR2A is written, this bit becomes set. When TCCR2A has been
updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates that TCCR2A
is ready to be updated with a new value.
Bit 7 6 5 4 3 2 1 0
– EXCLK AS2 TCN2UB OCR2AUB OCR2BUB TCR2AUB TCR2BUB ASSR
Read/Write R R/W R/W R R R R R
Initial Value 0 0 0 0 0 0 0 0
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• Bit 0 – TCR2BUB: Timer/Counter Control Register2 Update Busy
When Timer/Counter2 operates asynchronously and TCCR2B is written, this bit becomes set. When TCCR2B has been
updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates that TCCR2B
is ready to be updated with a new value.
If a write is performed to any of the five Timer/Counter2 registers while its update busy flag is set, the updated value might
get corrupted and cause an unintentional interrupt to occur.
The mechanisms for reading TCNT2, OCR2A, OCR2B, TCCR2A and TCCR2B are different. When reading TCNT2, the
actual timer value is read. When reading OCR2A, OCR2B, TCCR2A and TCCR2B the value in the temporary storage
register is read.
5.15.10 Timer/Counter Prescaler
Figure 5-64. Prescaler for Timer/Counter2
The clock source for Timer/Counter2 is named clkT2S. clkT2S is by default connected to the main system I/O clock clkIO. By
setting the AS2 bit in ASSR, Timer/Counter2 is asynchronously clocked from the TOSC1 pin. This enables use of
Timer/Counter2 as a real time counter (RTC). When AS2 is set, pins TOSC1 and TOSC2 are disconnected from port C. A
crystal can then be connected between the TOSC1 and TOSC2 pins to serve as an independent clock source for
Timer/Counter2. The oscillator is optimized for use with a 32.768kHz crystal. Applying an external clock source to TOSC1 is
not recommended.
For Timer/Counter2, the possible prescaled selections are: clkT2S/8, clkT2S/32, clkT2S/64, clkT2S/128, clkT2S/256, and
clkT2S/1024. Additionally, clkT2S as well as 0 (stop) may be selected. Setting the PSRASY bit in GTCCR resets the prescaler.
This allows the user to operate with a predictable prescaler.
Timer/Counter2 Clock Source
clkT2
clkT2S/8
clkT2S/32
clkT2S/64
clkT2S/128
clkT2S/256
clkT2S/1024
clkI/O
TOSC1
AS2
PSRASY
clkT2S 10-bit T/C Prescaler
0
Clear
CS20
CS21
CS22
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5.15.10.1 General Timer/Counter Control Register – GTCCR
• Bit 1 – PSRASY: Prescaler Reset Timer/Counter2
When this bit is one, the Timer/Counter2 prescaler will be reset. This bit is normally cleared immediately by hardware. If the
bit is written when Timer/Counter2 is operating in asynchronous mode, the bit will remain one until the prescaler has been
reset. The bit will not be cleared by hardware if the TSM bit is set. Refer to the description of the “Bit 7 – TSM: Timer/Counter
Synchronization Mode” for a description of the Timer/Counter synchronization mode.
5.16 Serial Peripheral Interface – SPI
The serial peripheral interface (SPI) allows high-speed synchronous data transfer between the Atmel®
ATA6612C/ATA6613C and peripheral devices or between several AVR® devices. The Atmel ATA6612C/ATA6613C SPI
includes the following features:
●Full-duplex, three-wire synchronous data transfer
●Master or slave operation
●LSB first or MSB first data transfer
●Seven programmable bit rates
●End of transmission interrupt flag
●Write collision flag protection
●Wake-up from idle mode
●Double speed (CK/2) master SPI mode
The USART can also be used in master SPI mode (see Section 5.18 “USART in SPI Mode” on page 186). The PRSPI bit in
Section 5.7.7.1 “Power Reduction Register - PRR” on page 58 must be written to zero to enable SPI module.
Bit 7 6 5 4 3 2 1 0
TSM – – – – – PSRASY PSRSYNC GTCCR
Read/Write R/W R R R R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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Figure 5-65. SPI Block Diagram(1)
Note: 1. Refer to Table 5-32 on page 84 for SPI pin placement.
The interconnection between master and slave CPUs with SPI is shown in Figure 5-66 on page 158. The system consists of
two shift registers, and a master clock generator. The SPI master initiates the communication cycle when pulling low the
slave select SS pin of the desired slave. master and slave prepare the data to be sent in their respective shift registers, and
the master generates the required clock pulses on the SCK line to interchange data. Data is always shifted from master to
slave on the master out – slave In, MOSI, line, and from slave to master on the master in – slave out, MISO, line. After each
data packet, the master will synchronize the slave by pulling high the slave select, SS, line.
When configured as a master, the SPI interface has no automatic control of the SS line. This must be handled by user
software before communication can start. When this is done, writing a byte to the SPI data register starts the SPI clock
generator, and the hardware shifts the eight bits into the slave. After shifting one byte, the SPI clock generator stops, setting
the end of transmission flag (SPIF). If the SPI interrupt enable bit (SPIE) in the SPCR register is set, an interrupt is
requested. The master may continue to shift the next byte by writing it into SPDR, or signal the end of packet by pulling high
the slave select, SS line. The last incoming byte will be kept in the buffer register for later use.
When configured as a slave, the SPI interface will remain sleeping with MISO tri-stated as long as the SS pin is driven high.
In this state, software may update the contents of the SPI data register, SPDR, but the data will not be shifted out by
incoming clock pulses on the SCK pin until the SS pin is driven low. As one byte has been completely shifted, the end of
transmission flag, SPIF is set. If the SPI interrupt enable bit, SPIE, in the SPCR register is set, an interrupt is requested. The
slave may continue to place new data to be sent into SPDR before reading the incoming data. The last incoming byte will be
kept in the buffer register for later use.
8-Bit Shift Register
Read Data Buffer
SPI Control RegisterSPI Status Register
MSTR
SPI Clock (Master)
SPE
SPI Control
SPI Interrupt
Request
Select Clock
Logic
MISO
Clock
8
88
S
M
S
M
M
S
MSB LSB
SPIE
SPE
WCOL
SPIF
SPI2X
SPI2X
SPR1
MSTR
SPE
DORD
SPR0
DORD
MSTR
CPOL
CPHA
SPR1
SPR0
MOSI
SCK
SS
Divider
/2/4/8/16/32/64/128
clkI/O
Internal
Data Bus
Pin
Control
Logic
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Figure 5-66. SPI Master-slave Interconnection
The system is single buffered in the transmit direction and double buffered in the receive direction. This means that bytes to
be transmitted cannot be written to the SPI data register before the entire shift cycle is completed. When receiving data,
however, a received character must be read from the SPI data register before the next character has been completely
shifted in. Otherwise, the first byte is lost.
In SPI slave mode, the control logic will sample the incoming signal of the SCK pin. To ensure correct sampling of the clock
signal, the frequency of the SPI clock should never exceed fosc/4.
When the SPI is enabled, the data direction of the MOSI, MISO, SCK, and SS pins is overridden according to Table 5-67. For
more details on automatic port overrides, refer to Section 5.10.3 “Alternate Port Functions” on page 81.
Table 5-67. SPI Pin Overrides(1)
Pin Direction, Master SPI Direction, Slave SPI
MOSI User defined Input
MISO Input User defined
SCK User defined Input
SS User defined Input
Note: 1. See Section 5.10.3.2 “Alternate Functions of Port B” on page 84 for a detailed description of how to define the
direction of the user defined SPI pins.
LSBSLAVEMSB
8 Bit Shift Register
LSB
Shift
Enable
MASTERMSB
SS
SCK
SS
SCK
MOSIMOSI
MISOMISO
8 Bit Shift Register
SPI
Clock Generator
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The following code examples show how to initialize the SPI as a master and how to perform a simple transmission.
DDR_SPI in the examples must be replaced by the actual data direction register controlling the SPI pins. DD_MOSI,
DD_MISO and DD_SCK must be replaced by the actual data direction bits for these pins. E.g. if MOSI is placed on pin PB5,
replace DD_MOSI with DDB5 and DDR_SPI with DDRB.
Note: 1. The example code assumes that the part specific header file is included.
Assembly Code Example(1)
SPI_MasterInit:
; Set MOSI and SCK output, all others input
ldi r17,(1<<DD_MOSI)|(1<<DD_SCK)
out DDR_SPI,r17
; Enable SPI, Master, set clock rate fck/16
ldi r17,(1<<SPE)|(1<<MSTR)|(1<<SPR0)
out SPCR,r17
ret
SPI_MasterTransmit:
; Start transmission of data (r16)
out SPDR,r16
Wait_Transmit:
; Wait for transmission complete
sbis SPSR,SPIF
rjmp Wait_Transmit
ret
C Code Example(1)
void SPI_MasterInit(void)
{
/* Set MOSI and SCK output, all others input */
DDR_SPI = (1<<DD_MOSI)|(1<<DD_SCK);
/* Enable SPI, Master, set clock rate fck/16 */
SPCR = (1<<SPE)|(1<<MSTR)|(1<<SPR0);
}
void SPI_MasterTransmit(char cData)
{
/* Start transmission */
SPDR = cData;
/* Wait for transmission complete */
while(!(SPSR & (1<<SPIF)))
;
}
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The following code examples show how to initialize the SPI as a slave and how to perform a simple reception.
Note: 1. The example code assumes that the part specific header file is included.
5.16.1 SS Pin Functionality
5.16.1.1 Slave Mode
When the SPI is configured as a slave, the slave select (SS) pin is always input. When SS is held low, the SPI is activated,
and MISO becomes an output if configured so by the user. All other pins are inputs. When SS is driven high, all pins are
inputs, and the SPI is passive, which means that it will not receive incoming data. Note that the SPI logic will be reset once
the SS pin is driven high.
The SS pin is useful for packet/byte synchronization to keep the slave bit counter synchronous with the master clock
generator. When the SS pin is driven high, the SPI slave will immediately reset the send and receive logic, and drop any
partially received data in the shift register.
Assembly Code Example(1)
SPI_SlaveInit:
; Set MISO output, all others input
ldi r17,(1<<DD_MISO)
out DDR_SPI,r17
; Enable SPI
ldi r17,(1<<SPE)
out SPCR,r17
ret
SPI_SlaveReceive:
; Wait for reception complete
sbis SPSR,SPIF
rjmp SPI_SlaveReceive
; Read received data and return
in r16,SPDR
ret
C Code Example(1)
void SPI_SlaveInit(void)
{
/* Set MISO output, all others input */
DDR_SPI = (1<<DD_MISO);
/* Enable SPI */
SPCR = (1<<SPE);
}
char SPI_SlaveReceive(void)
{
/* Wait for reception complete */
while(!(SPSR & (1<<SPIF)))
;
/* Return Data Register */
return SPDR;
}
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5.16.1.2 Master Mode
When the SPI is configured as a master (MSTR in SPCR is set), the user can determine the direction of the SS pin.
If SS is configured as an output, the pin is a general output pin which does not affect the SPI system. Typically, the pin will be
driving the SS pin of the SPI slave.
If SS is configured as an input, it must be held high to ensure master SPI operation. If the SS pin is driven low by peripheral
circuitry when the SPI is configured as a master with the SS pin defined as an input, the SPI system interprets this as
another master selecting the SPI as a slave and starting to send data to it. To avoid bus contention, the SPI system takes the
following actions:
1. The MSTR bit in SPCR is cleared and the SPI system becomes a slave. As a result of the SPI becoming a slave,
the MOSI and SCK pins become inputs.
2. The SPIF flag in SPSR is set, and if the SPI interrupt is enabled, and the I-bit in SREG is set, the interrupt routine
will be executed.
Thus, when interrupt-driven SPI transmission is used in master mode, and there exists a possibility that SS is driven low, the
interrupt should always check that the MSTR bit is still set. If the MSTR bit has been cleared by a slave select, it must be set
by the user to re-enable SPI master mode.
5.16.1.3 SPI Control Register – SPCR
• Bit 7 – SPIE: SPI Interrupt Enable
This bit causes the SPI interrupt to be executed if SPIF bit in the SPSR register is set and the if the global interrupt enable bit
in SREG is set.
• Bit 6 – SPE: SPI Enable
When the SPE bit is written to one, the SPI is enabled. This bit must be set to enable any SPI operations.
• Bit 5 – DORD: Data Order
When the DORD bit is written to one, the LSB of the data word is transmitted first.
When the DORD bit is written to zero, the MSB of the data word is transmitted first.
• Bit 4 – MSTR: Master/Slave Select
This bit selects master SPI mode when written to one, and slave SPI mode when written logic zero. If SS is configured as an
input and is driven low while MSTR is set, MSTR will be cleared, and SPIF in SPSR will become set. The user will then have
to set MSTR to re-enable SPI master mode.
• Bit 3 – CPOL: Clock Polarity
When this bit is written to one, SCK is high when idle. When CPOL is written to zero, SCK is low when idle. Refer to
Figure 5-67 on page 163 and Figure 5-68 on page 164 for an example. The CPOL functionality is summarized below:
Bit 76543210
SPIE SPE DORD MSTR CPOL CPHA SPR1 SPR0 SPCR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 5-68. CPOL Functionality
CPOL Leading Edge Trailing Edge
0Rising Falling
1Falling Rising
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• Bit 2 – CPHA: Clock Phase
The settings of the clock phase bit (CPHA) determine if data is sampled on the leading (first) or trailing (last) edge of SCK.
Refer to Figure 5-67 on page 163 and Figure 5-68 on page 164 for an example. The CPOL functionality is summarized
below:
• Bits 1, 0 – SPR1, SPR0: SPI Clock Rate Select 1 and 0
These two bits control the SCK rate of the device configured as a master. SPR1 and SPR0 have no effect on the slave. The
relationship between SCK and the oscillator clock frequency fosc is shown in the following table:
5.16.1.4 SPI Status Register – SPSR
• Bit 7 – SPIF: SPI Interrupt Flag
When a serial transfer is complete, the SPIF flag is set. An interrupt is generated if SPIE in SPCR is set and global interrupts
are enabled. If SS is an input and is driven low when the SPI is in master mode, this will also set the SPIF flag. SPIF is
cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, the SPIF bit is cleared by
first reading the SPI status register with SPIF set, then accessing the SPI data register (SPDR).
• Bit 6 – WCOL: Write COLlision Flag
The WCOL bit is set if the SPI data register (SPDR) is written during a data transfer. The WCOL bit (and the SPIF bit) are
cleared by first reading the SPI status register with WCOL set, and then accessing the SPI data register.
• Bit 5..1 – Res: Reserved Bits
These bits are reserved bits in the Atmel® ATA6612C/ATA6613C and will always read as zero.
Table 5-69. CPHA Functionality
CPHA Leading Edge Trailing Edge
0Sample Setup
1Setup Sample
Table 5-70. Relationship Between SCK and the Oscillator Frequency
SPI2X SPR1 SPR0 SCK Frequency
0 0 0 fosc/4
0 0 1 fosc/16
0 1 0 fosc/64
0 1 1 fosc/128
1 0 0 fosc/2
1 0 1 fosc/8
1 1 0 fosc/32
1 1 1 fosc/64
Bit 76543210
SPIFWCOL–––––SPI2XSPSR
Read/Write RRRRRRRR/W
Initial Value00000000
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• Bit 0 – SPI2X: Double SPI Speed Bit
When this bit is written logic one the SPI speed (SCK frequency) will be doubled when the SPI is in master mode
(see Table 5-70 on page 162). This means that the minimum SCK period will be two CPU clock periods. When the SPI is
configured as slave, the SPI is only guaranteed to work at fosc/4 or lower.
The SPI interface on the Atmel® ATA6612C/ATA6613C is also used for program memory and EEPROM downloading or
uploading. See Section 5.24.8 “Serial Downloading” on page 267 for serial programming and verification.
5.16.1.5 SPI Data Register – SPDR
The SPI data register is a read/write register used for data transfer between the register file and the SPI shift register. Writing
to the register initiates data transmission. Reading the register causes the shift register receive buffer to be read.
5.16.2 Data Modes
There are four combinations of SCK phase and polarity with respect to serial data, which are determined by control bits
CPHA and CPOL. The SPI data transfer formats are shown in Figure 5-67 and Figure 5-68 on page 164. Data bits are
shifted out and latched in on opposite edges of the SCK signal, ensuring sufficient time for data signals to stabilize. This is
clearly seen by summarizing Table 5-68 on page 161 and Table 5-69 on page 162, as done below.
Figure 5-67. SPI Transfer Format with CPHA = 0
Bit 76543210
MSB LSB SPDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial ValueXXXXXXXXUndefined
Table 5-71. CPOL Functionality
Leading Edge Trailing eDge SPI Mode
CPOL = 0, CPHA = 0 Sample (rising) Setup (falling) 0
CPOL = 0, CPHA = 1 Setup (rising) Sample (falling) 1
CPOL = 1, CPHA = 0 Sample (falling) Setup (rising) 2
CPOL = 1, CPHA = 1 Setup (falling) Sample (rising) 3
LSB
MSB
Bit 1
Bit 6
Bit 2
Bit 5
Bit 3
Bit 4
Bit 4
Bit 3
Bit 5
Bit 2
Bit 6
Bit 1
MSB
LSB
MSB first (DORD = 0)
LSB first (DORD =1)
SCK (CPOL = 0)
Mode 0
SCK (CPOL = 1)
Mode 2
SS
SAMPLE I
MOSI/MISO
CHANGE 0
MOSI PIN
CHANGE 0
MISO PIN
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Figure 5-68. SPI Transfer Format with CPHA = 1
5.17 USART0
The universal synchronous and asynchronous serial receiver and transmitter (USART) is a highly flexible serial
communication device. The main features are:
●Full duplex operation (independent serial receive and transmit registers)
●Asynchronous or synchronous operation
●Master or slave clocked synchronous operation
●High resolution baud rate generator
●Supports serial frames with 5, 6, 7, 8, or 9 data bits and 1 or 2 stop bits
●Odd or even parity generation and parity check supported by hardware
●Data overrun detection
●Framing error detection
●Noise filtering includes false start bit detection and digital low pass filter
●Three separate interrupts on TX complete, TX data register empty and RX complete
●Multi-processor communication mode
●Double speed asynchronous communication mode
The USART can also be used in master SPI mode (see Section 5.18 “USART in SPI Mode” on page 186. The power
reduction USART bit, PRUSART0, in Section 5.7.7.1 “Power Reduction Register - PRR” on page 58 must be disabled by
writing a logical zero to it.
LSB
MSB
Bit 1
Bit 6
Bit 2
Bit 5
Bit 3
Bit 4
Bit 4
Bit 3
Bit 5
Bit 2
Bit 6
Bit 1
MSB
LSB
MSB first (DORD = 0)
LSB first (DORD =1)
SCK (CPOL = 0)
Mode 1
SCK (CPOL = 1)
Mode 3
SS
SAMPLE I
MOSI/MISO
CHANGE 0
MOSI PIN
CHANGE 0
MISO PIN
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5.17.1 Overview
A simplified block diagram of the USART transmitter is shown in Figure 5-69. CPU accessible I/O registers and I/O pins are
shown in bold.
Figure 5-69. USART Block Diagram(1)
Note: 1. Refer to Table 5-38 on page 89 for USART0 pin placement.
The dashed boxes in the block diagram separate the three main parts of the USART (listed from the top): Clock generator,
transmitter and receiver. Control registers are shared by all units. The clock generation logic consists of synchronization
logic for external clock input used by synchronous slave operation, and the baud rate generator. The XCKn (transfer clock)
pin is only used by synchronous transfer mode. The transmitter consists of a single write buffer, a serial shift register, parity
generator and control logic for handling different serial frame formats. The write buffer allows a continuous transfer of data
without any delay between frames. The receiver is the most complex part of the USART module due to its clock and data
recovery units. The recovery units are used for asynchronous data reception. In addition to the recovery units, the receiver
includes a parity checker, control logic, a shift register and a two level receive buffer (UDRn). The receiver supports the
same frame formats as the transmitter, and can detect frame error, data overrun and parity errors.
Transmit Shift Register
Receive Shift Register Data
Recovery
Clock
Recovery
Parity
Checker
Parity
Generator
Pin
Control
TX
Control
Pin
Control
Pin
Control
RX
Control
UDRn (Transmit)
Transmitter
Clock Generator
Receiver
UCSRnA UCSRnB UCSRnC
Sync Logic
OSC
UDR (Receive)
DATA BUS
Baud Rate Generator
UBRR[H:L]
XCKn
RxDn
TxDn
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5.17.2 Clock Generation
The clock generation logic generates the base clock for the transmitter and receiver. The USART supports four modes of
clock operation: Normal asynchronous, double speed asynchronous, master synchronous and slave synchronous mode.
The UMSELn bit in USART control and status register C (UCSRnC) selects between asynchronous and synchronous
operation. Double speed (asynchronous mode only) is controlled by the U2Xn found in the UCSRnA register. When using
synchronous mode (UMSELn = 1), the data direction register for the XCKn pin (DDR_XCKn) controls whether the clock
source is internal (master mode) or external (slave mode). The XCKn pin is only active when using synchronous mode.
Figure 5-70 shows a block diagram of the clock generation logic.
Figure 5-70. Clock Generation Logic, Block Diagram
Signal description:
txclk Transmitter clock (internal signal).
rxclk Receiver base clock (internal signal).
xcki Input from XCK pin (internal signal). Used for synchronous slave operation.
xcko Clock output to XCK pin (internal signal). Used for synchronous master operation.
fosc XTAL pin frequency (system clock).
5.17.2.1 Internal Clock Generation – The Baud Rate Generator
Internal clock generation is used for the asynchronous and the synchronous master modes of operation. The description in
this section refers to Figure 5-70.
The USART baud rate register (UBRRn) and the down-counter connected to it function as a programmable prescaler or
baud rate generator. The down-counter, running at system clock (fosc), is loaded with the UBRRn value each time the
counter has counted down to zero or when the UBRRnL register is written. A clock is generated each time the counter
reaches zero. This clock is the baud rate generator clock output (= fosc/(UBRRn+1)). The transmitter divides the baud rate
generator clock output by 2, 8 or 16 depending on mode. The baud rate generator output is used directly by the receiver’s
clock and data recovery units. However, the recovery units use a state machine that uses 2, 8 or 16 states depending on
mode set by the state of the UMSELn, U2Xn and DDR_XCKn bits.
Sync
Register
Edge
Detector
Prescaling
Down-Counter /2
XCKn
Pin
/4 0
0
1
1
0
1
0
1
/2
UBRRn
DDR_XCKn UCPOLn
U2Xn
DDR_XCKn
UBRRn+1
txclk
rxclk
UMSELn
foscn
OSC
xcki
xcko
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Table 5-72 contains equations for calculating the baud rate (in bits per second) and for calculating the UBRRn value for each
mode of operation using an internally generated clock source.
BAUD Baud rate (in bits per second, bps)
fOSC System Oscillator clock frequency
UBRRn Contents of the UBRRnH and UBRRnL Registers, (0-4095)
Some examples of UBRRn values for some system clock frequencies are found in Table 5-80 on page 184 (see Section 5-80
“Examples of UBRRn Settings for Commonly Used Oscillator Frequencies” on page 184).
5.17.2.2 Double Speed Operation (U2Xn)
The transfer rate can be doubled by setting the U2Xn bit in UCSRnA. Setting this bit only has effect for the asynchronous
operation. Set this bit to zero when using synchronous operation.Setting this bit will reduce the divisor of the baud rate
divider from 16 to 8, effectively doubling the transfer rate for asynchronous communication.
Note however that the receiver will in this case only use half the number of samples (reduced from 16 to 8) for data sampling
and clock recovery, and therefore a more accurate baud rate setting and system clock are required when this mode is used.
For the transmitter, there are no downsides.
5.17.2.3 External Clock
External clocking is used by the synchronous slave modes of operation. The description in this section refers to
Figure 5-70 on page 166 for details.
External clock input from the XCKn pin is sampled by a synchronization register to minimize the chance of meta-stability.
The output from the synchronization register must then pass through an edge detector before it can be used by the
transmitter and receiver. This process introduces a two CPU clock period delay and therefore the maximum external XCKn
clock frequency is limited by the following equation:
Note that fosc depends on the stability of the system clock source. It is therefore recommended to add some margin to avoid
possible loss of data due to frequency variations.
Table 5-72. Equations for Calculating Baud Rate Register Setting
Operating Mode Equation for Calculating Baud Rate(1) Equation for Calculating UBRRn Value
Asynchronous normal mode
(U2Xn = 0)
Asynchronous double speed
mode (U2Xn = 1)
Synchronous master mode
Note: 1. The baud rate is defined to be the transfer rate in bit per second (bps)
BAUD fOSC
16 UBRRn 1+()
---------------------------------------
=
UBRRn fOSC
16BAUD
-----------------------1–=
BAUD fOSC
8 UBRRn 1+()
------------------------------------
=
UBRRn fOSC
8BAUD
--------------------1–=
BAUD fOSC
2 UBRRn 1+()
------------------------------------
=
UBRRn fOSC
2BAUD
--------------------1–=
fXCK
fOSC
4
-----------
<
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5.17.2.4 Synchronous Clock Operation
When synchronous mode is used (UMSELn = 1), the XCKn pin will be used as either clock input (slave) or clock output
(master). The dependency between the clock edges and data sampling or data change is the same. The basic principle is
that data input (on RxDn) is sampled at the opposite XCKn clock edge of the edge the data output (TxDn) is changed.
Figure 5-71. Synchronous Mode XCKn Timing
The UCPOLn bit UCRSC selects which XCKn clock edge is used for data sampling and which is used for data change. As
Figure 5-71 shows, when UCPOLn is zero the data will be changed at rising XCKn edge and sampled at falling XCKn edge.
If UCPOLn is set, the data will be changed at falling XCKn edge and sampled at rising XCKn edge.
5.17.3 Frame Formats
A serial frame is defined to be one character of data bits with synchronization bits (start and stop bits), and optionally a parity
bit for error checking. The USART accepts all 30 combinations of the following as valid frame formats:
●1 start bit
●5, 6, 7, 8, or 9 data bits
●no, even or odd parity bit
●1 or 2 stop bits
A frame starts with the start bit followed by the least significant data bit. Then the next data bits, up to a total of nine, are
succeeding, ending with the most significant bit. If enabled, the parity bit is inserted after the data bits, before the stop bits.
When a complete frame is transmitted, it can be directly followed by a new frame, or the communication line can be set to an
idle (high) state. Figure 5-72 illustrates the possible combinations of the frame formats. Bits inside brackets are optional.
Figure 5-72. Frame Formats
St Start bit, always low.
(n) Data bits (0 to 8).
PParity bit. Can be odd or even.
Sp Stop bit, always high.
IDLE No transfers on the communication line (RxDn or TxDn). An IDLE line must be high.
The frame format used by the USART is set by the UCSZn2:0, UPMn1:0 and USBSn bits in UCSRnB and UCSRnC. The
receiver and transmitter use the same setting. Note that changing the setting of any of these bits will corrupt all ongoing
communication for both the receiver and transmitter.
XCK
RxD/TxD
XCK
UCPOL = 1
UCPOL = 0
RxD/TxD
Sample
Sample
ST 0 1 2 3 4 [5] [6] [7] [8] (St/IDLE)(IDLE)
FRAME
[P] Sp1 [Sp2]
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The USART character size (UCSZn2:0) bits select the number of data bits in the frame. The USART parity mode (UPMn1:0)
bits enable and set the type of parity bit. The selection between one or two stop bits is done by the USART stop bit select
(USBSn) bit. The Receiver ignores the second stop bit. An FE (frame error) will therefore only be detected in the cases
where the first stop bit is zero.
5.17.3.1 Parity Bit Calculation
The parity bit is calculated by doing an exclusive-or of all the data bits. If odd parity is used, the result of the exclusive or is
inverted. The relation between the parity bit and data bits is as follows:
Peven Parity bit using even parity
Podd Parity bit using odd parity
dnData bit n of the character
If used, the parity bit is located between the last data bit and first stop bit of a serial frame.
5.17.4 USART Initialization
The USART has to be initialized before any communication can take place. The initialization process normally consists of
setting the baud rate, setting frame format and enabling the transmitter or the receiver depending on the usage. For interrupt
driven USART operation, the global interrupt flag should be cleared (and interrupts globally disabled) when doing the
initialization.
Before doing a re-initialization with changed baud rate or frame format, be sure that there are no ongoing transmissions
during the period the registers are changed. The TXCn flag can be used to check that the transmitter has completed all
transfers, and the RXC flag can be used to check that there are no unread data in the receive buffer. Note that the TXCn flag
must be cleared before each transmission (before UDRn is written) if it is used for this purpose.
Peven dn1–…d3d2d1d00
Podd
⊕⊕⊕⊕⊕⊕
dn1–…d3d2d1d01⊕⊕⊕⊕⊕⊕
=
=
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The following simple USART initialization code examples show one assembly and one C function that are equal in
functionality. The examples assume asynchronous operation using polling (no interrupts enabled) and a fixed frame format.
The baud rate is given as a function parameter. For the assembly code, the baud rate parameter is assumed to be stored in
the r17:r16 registers.
Note: 1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must
be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with
“SBRS”, “SBRC”, “SBR”, and “CBR”.
More advanced initialization routines can be made that include frame format as parameters, disable interrupts and so on.
However, many applications use a fixed setting of the baud and control registers, and for these types of applications the
initialization code can be placed directly in the main routine, or be combined with initialization code for other I/O modules.
5.17.5 Data Transmission – The USART Transmitter
The USART transmitter is enabled by setting the transmit enable (TXEN) bit in the UCSRnB register. When the transmitter is
enabled, the normal port operation of the TxDn pin is overridden by the USART and given the function as the transmitter’s
serial output. The baud rate, mode of operation and frame format must be set up once before doing any transmissions. If
synchronous operation is used, the clock on the XCKn pin will be overridden and used as transmission clock.
5.17.5.1 Sending Frames with 5 to 8 Data Bit
A data transmission is initiated by loading the transmit buffer with the data to be transmitted. The CPU can load the transmit
buffer by writing to the UDRn I/O location. The buffered data in the transmit buffer will be moved to the shift register when the
shift register is ready to send a new frame. The shift register is loaded with new data if it is in idle state (no ongoing
transmission) or immediately after the last stop bit of the previous frame is transmitted. When the shift register is loaded with
new data, it will transfer one complete frame at the rate given by the baud register, U2Xn bit or by XCKn depending on mode
of operation.
Assembly Code Example(1)
USART_Init:
; Set baud rate
out UBRRnH, r17
out UBRRnL, r16
; Enable receiver and transmitter
ldi r16, (1<<RXENn)|(1<<TXENn)
out UCSRnB,r16
; Set frame format: 8data, 2stop bit
ldi r16, (1<<USBSn)|(3<<UCSZn0)
out UCSRnC,r16
ret
C Code Example(1)
void USART_Init(unsigned int baud)
{
/* Set baud rate */
UBRRnH = (unsigned char)(baud>>8);
UBRRnL = (unsigned char)baud;
/* Enable receiver and transmitter */
UCSRnB = (1<<RXENn)|(1<<TXENn);
/* Set frame format: 8data, 2stop bit */
UCSRnC = (1<<USBSn)|(3<<UCSZn0);
}
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The following code examples show a simple USART transmit function based on polling of the data register empty (UDREn)
flag. When using frames with less than eight bits, the most significant bits written to the UDRn are ignored. The USART has
to be initialized before the function can be used. For the assembly code, the data to be sent is assumed to be stored in
register R16.
Note: 1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must
be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with
“SBRS”, “SBRC”, “SBR”, and “CBR”.
The function simply waits for the transmit buffer to be empty by checking the UDREn flag, before loading it with new data to
be transmitted. If the data register empty interrupt is utilized, the interrupt routine writes the data into the buffer.
Assembly Code Example(1)
USART_Transmit:
; Wait for empty transmit buffer
sbis UCSRnA,UDREn
rjmp USART_Transmit
; Put data (r16) into buffer, sends the data
out UDRn,r16
ret
C Code Example(1)
void USART_Transmit (unsigned char data)
{
/* Wait for empty transmit buffer */
while (!(UCSRnA & (1<<UDREn)))
;
/* Put data into buffer, sends the data */
UDRn = data;
}
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5.17.5.2 Sending Frames with 9 Data Bit
If 9-bit characters are used (UCSZn = 7), the ninth bit must be written to the TXB8 bit in UCSRnB before the low byte of the
character is written to UDRn. The following code examples show a transmit function that handles 9-bit characters. For the
assembly code, the data to be sent is assumed to be stored in registers R17:R16.
Notes: 1. These transmit functions are written to be general functions. They can be optimized if the contents of the UCS-
RnB is static. For example, only the TXB8 bit of the UCSRnB register is used after initialization.
2. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must
be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with
“SBRS”, “SBRC”, “SBR”, and “CBR”.
The ninth bit can be used for indicating an address frame when using multi processor communication mode or for other
protocol handling as for example synchronization.
5.17.5.3 Transmitter Flags and Interrupts
The USART transmitter has two flags that indicate its state: USART data register empty (UDREn) and transmit complete
(TXCn). Both flags can be used for generating interrupts.
The data register empty (UDREn) flag indicates whether the transmit buffer is ready to receive new data. This bit is set when
the transmit buffer is empty, and cleared when the transmit buffer contains data to be transmitted that has not yet been
moved into the shift register. For compatibility with future devices, always write this bit to zero when writing the UCSRnA
register.
When the data register empty interrupt enable (UDRIEn) bit in UCSRnB is written to one, the USART data register empty
interrupt will be executed as long as UDREn is set (provided that global interrupts are enabled). UDREn is cleared by writing
UDRn. When interrupt-driven data transmission is used, the data register empty interrupt routine must either write new data
to UDRn in order to clear UDREn or disable the data register empty interrupt, otherwise a new interrupt will occur once the
interrupt routine terminates.
The transmit complete (TXCn) flag bit is set one when the entire frame in the transmit shift register has been shifted out and
there are no new data currently present in the transmit buffer. The TXCn flag bit is automatically cleared when a transmit
complete interrupt is executed, or it can be cleared by writing a one to its bit location. The TXCn flag is useful in half-duplex
communication interfaces (like the RS-485 standard), where a transmitting application must enter receive mode and free the
communication bus immediately after completing the transmission.
Assembly Code Example(1)(2)
USART_Transmit:
; Wait for empty transmit buffer
sbis UCSRnA,UDREn
rjmp USART_Transmit
; Copy 9th bit from r17 to TXB8
cbi UCSRnB,TXB8
sbrc r17,0
sbi UCSRnB,TXB8
; Put LSB data (r16) into buffer, sends the data
out UDRn,r16
ret
C Code Example(1)(2)
void USART_Transmit (unsigned int data)
{
/* Wait for empty transmit buffer */
while (!(UCSRnA & (1<<UDREn))))
;
/* Copy 9th bit to TXB8 */
UCSRnB &= ~(1<<TXB8);
if (data & 0x0100)
UCSRnB |= (1<<TXB8);
/* Put data into buffer, sends the data */
UDRn = data;
}
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When the transmit compete interrupt enable (TXCIEn) bit in UCSRnB is set, the USART transmit complete interrupt will be
executed when the TXCn flag becomes set (provided that global interrupts are enabled). When the transmit complete
interrupt is used, the interrupt handling routine does not have to clear the TXCn flag, this is done automatically when the
interrupt is executed.
5.17.5.4 Parity Generator
The parity generator calculates the parity bit for the serial frame data. When parity bit is enabled (UPMn1 = 1), the
transmitter control logic inserts the parity bit between the last data bit and the first stop bit of the frame that is sent.
5.17.5.5 Disabling the Transmitter
The disabling of the transmitter (setting the TXEN to zero) will not become effective until ongoing and pending transmissions
are completed, i.e., when the transmit shift register and transmit buffer register do not contain data to be transmitted. When
disabled, the transmitter will no longer override the TxDn pin.
5.17.6 Data Reception – The USART Receiver
The USART receiver is enabled by writing the receive enable (RXENn) bit in the
UCSRnB register to one. When the receiver is enabled, the normal pin operation of the RxDn pin is overridden by the
USART and given the function as the receiver’s serial input. The baud rate, mode of operation and frame format must be set
up once before any serial reception can be done. If synchronous operation is used, the clock on the XCKn pin will be used as
transfer clock.
5.17.6.1 Receiving Frames with 5 to 8 Data Bits
The receiver starts data reception when it detects a valid start bit. Each bit that follows the start bit will be sampled at the
baud rate or XCKn clock, and shifted into the receive shift register until the first stop bit of a frame is received. A second stop
bit will be ignored by the receiver. When the first stop bit is received, i.e., a complete serial frame is present in the receive
shift register, the contents of the shift register will be moved into the receive buffer. The receive buffer can then be read by
reading the UDRn I/O location.
The following code example shows a simple USART receive function based on polling of the receive complete (RXCn) flag.
When using frames with less than eight bits the most significant bits of the data read from the UDRn will be masked to zero.
The USART has to be initialized before the function can be used.
Note: 1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must
be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with
“SBRS”, “SBRC”, “SBR”, and “CBR”.
The function simply waits for data to be present in the receive buffer by checking the RXCn flag, before reading the buffer
and returning the value.
Assembly Code Example(1)
USART_Receive:
; Wait for data to be received
sbis UCSRnA, RXCn
rjmp USART_Receive
; Get and return received data from buffer
in r16, UDRn
ret
C Code Example(1)
unsigned char USART_Receive(void)
{
/* Wait for data to be received */
while (!(UCSRnA & (1<<RXCn)))
;
/* Get and return received data from buffer */
return UDRn;
}
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5.17.6.2 Receiving Frames with 9 Data Bits
If 9-bit characters are used (UCSZn=7) the ninth bit must be read from the RXB8n bit in UCSRnB before reading the low bits
from the UDRn. This rule applies to the FEn, DORn and UPEn status flags as well. Read status from UCSRnA, then data
from UDRn. Reading the UDRn I/O location will change the state of the receive buffer FIFO and consequently the TXB8n,
FEn, DORn and UPEn bits, which all are stored in the FIFO, will change.
The following code example shows a simple USART receive function that handles both nine bit characters and the status
bits.
Note: 1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must
be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with
“SBRS”, “SBRC”, “SBR”, and “CBR”.
The receive function example reads all the I/O registers into the register file before any computation is done. This gives an
optimal receive buffer utilization since the buffer location read will be free to accept new data as early as possible.
Assembly Code Example(1)
USART_Receive:
; Wait for data to be received
sbis UCSRnA, RXCn
rjmp USART_Receive
; Get status and 9th bit, then data from buffer
in r18, UCSRnA
in r17, UCSRnB
in r16, UDRn
; If error, return -1
andi r18,(1<<FEn)|(1<<DORn)|(1<<UPEn)
breq USART_ReceiveNoError
ldi r17, HIGH(-1)
ldi r16, LOW(-1)
USART_ReceiveNoError:
; Filter the 9th bit, then return
lsr r17
andi r17, 0x01
ret
C Code Example(1)
unsigned int USART_Receive( void )
{
unsigned char status, resh, resl;
/* Wait for data to be received */
while (!(UCSRnA & (1<<RXCn)))
;
/* Get status and 9th bit, then data */
/* from buffer */
status = UCSRnA;
resh = UCSRnB;
resl = UDRn;
/* If error, return -1 */
if (status & (1<<FEn)|(1<<DORn)|(1<<UPEn))
return -1;
/* Filter the 9th bit, then return */
resh = (resh >> 1) & 0x01;
return ((resh << 8) | resl);
}
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5.17.6.3 Receive Compete Flag and Interrupt
The USART receiver has one flag that indicates the receiver state.
The receive complete (RXCn) flag indicates if there are unread data present in the receive buffer. This flag is one when
unread data exist in the receive buffer, and zero when the receive buffer is empty (i.e., does not contain any unread data). If
the receiver is disabled (RXENn = 0), the receive buffer will be flushed and consequently the RXCn bit will become zero.
When the receive complete Interrupt enable (RXCIEn) in UCSRnB is set, the USART receive complete interrupt will be
executed as long as the RXCn flag is set (provided that global interrupts are enabled). When interrupt-driven data reception
is used, the receive complete routine must read the received data from UDRn in order to clear the RXCn flag, otherwise a
new interrupt will occur once the interrupt routine terminates.
5.17.6.4 Receiver Error Flags
The USART receiver has three error flags: Frame error (FEn), data overrun (DORn) and parity error (UPEn). All can be
accessed by reading UCSRnA. Common for the error flags is that they are located in the receive buffer together with the
frame for which they indicate the error status. Due to the buffering of the error flags, the UCSRnA must be read before the
receive buffer (UDRn), since reading the UDRn I/O location changes the buffer read location. Another equality for the error
flags is that they can not be altered by software doing a write to the flag location. However, all flags must be set to zero when
the UCSRnA is written for upward compatibility of future USART implementations. None of the error flags can generate
interrupts.
The frame error (FEn) flag indicates the state of the first stop bit of the next readable frame stored in the receive buffer. The
FEn flag is zero when the stop bit was correctly read (as one), and the FEn flag will be one when the stop bit was incorrect
(zero). This flag can be used for detecting out-of-sync conditions, detecting break conditions and protocol handling. The FEn
flag is not affected by the setting of the USBSn bit in UCSRnC since the receiver ignores all, except for the first, stop bits. For
compatibility with future devices, always set this bit to zero when writing to UCSRnA.
The data overrun (DORn) flag indicates data loss due to a receiver buffer full condition. A data overrun occurs when the
receive buffer is full (two characters), it is a new character waiting in the receive shift register, and a new start bit is detected.
If the DORn flag is set there was one or more serial frame lost between the frame last read from UDRn, and the next frame
read from UDRn. For compatibility with future devices, always write this bit to zero when writing to UCSRnA. The DORn flag
is cleared when the frame received was successfully moved from the shift register to the receive buffer.
The parity error (UPEn) flag indicates that the next frame in the receive buffer had a parity error when received. If parity
check is not enabled the UPEn bit will always be read zero. For compatibility with future devices, always set this bit to zero
when writing to UCSRnA. For more details see Section 5.17.3.1 “Parity Bit Calculation” on page 169 and
Section 5.17.6.5 “Parity Checker” on page 175.
5.17.6.5 Parity Checker
The parity checker is active when the high USART parity mode (UPMn1) bit is set. Type of parity check to be performed (odd
or even) is selected by the UPMn0 bit. When enabled, the parity checker calculates the parity of the data bits in incoming
frames and compares the result with the parity bit from the serial frame. The result of the check is stored in the receive buffer
together with the received data and stop bits. The parity error (UPEn) flag can then be read by software to check if the frame
had a parity error.
The UPEn bit is set if the next character that can be read from the receive buffer had a parity error when received and the
parity checking was enabled at that point (UPMn1 = 1). This bit is valid until the receive buffer (UDRn) is read.
5.17.6.6 Disabling the Receiver
In contrast to the transmitter, disabling of the receiver will be immediate. Data from ongoing receptions will therefore be lost.
When disabled (i.e., the RXENn is set to zero) the receiver will no longer override the normal function of the RxDn port pin.
The receiver buffer FIFO will be flushed when the receiver is disabled. Remaining data in the buffer will be lost.
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5.17.6.7 Flushing the Receive Buffer
The receiver buffer FIFO will be flushed when the receiver is disabled, i.e., the buffer will be emptied of its contents. Unread
data will be lost. If the buffer has to be flushed during normal operation, due to for instance an error condition, read the UDRn
I/O location until the RXCn flag is cleared. The following code example shows how to flush the receive buffer.
Note: 1. The example code assumes that the part specific header file is included.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must
be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with
“SBRS”, “SBRC”, “SBR”, and “CBR”.
5.17.7 Asynchronous Data Reception
The USART includes a clock recovery and a data recovery unit for handling asynchronous data reception. The clock
recovery logic is used for synchronizing the internally generated baud rate clock to the incoming asynchronous serial frames
at the RxDn pin. The data recovery logic samples and low pass filters each incoming bit, thereby improving the noise
immunity of the receiver. The asynchronous reception operational range depends on the accuracy of the internal baud rate
clock, the rate of the incoming frames, and the frame size in number of bits.
5.17.7.1 Asynchronous Clock Recovery
The clock recovery logic synchronizes internal clock to the incoming serial frames. Figure 5-73 illustrates the sampling
process of the start bit of an incoming frame. The sample rate is 16 times the baud rate for normal mode, and eight times the
baud rate for double speed mode. The horizontal arrows illustrate the synchronization variation due to the sampling process.
Note the larger time variation when using the double speed mode (U2Xn = 1) of operation. Samples denoted zero are
samples done when the RxDn line is idle (i.e., no communication activity).
Figure 5-73. Start Bit Sampling
When the clock recovery logic detects a high (idle) to low (start) transition on the RxDn line, the start bit detection sequence
is initiated. Let sample 1 denote the first zero-sample as shown in the figure. The clock recovery logic then uses samples 8,
9, and 10 for normal mode, and samples 4, 5, and 6 for double speed mode (indicated with sample numbers inside boxes on
the figure), to decide if a valid start bit is received. If two or more of these three samples have logical high levels (the majority
wins), the start bit is rejected as a noise spike and the receiver starts looking for the next high to low-transition. If however, a
valid start bit is detected, the clock recovery logic is synchronized and the data recovery can begin. The synchronization
process is repeated for each start bit.
Assembly Code Example(1)
USART_Flush:
sbis UCSRnA, RXCn
ret
in r16, UDRn
rjmp USART_Flush
C Code Example(1)
void USART_Flush (void)
{
unsigned char dummy;
while (UCSRnA & (1<<RXCn)) dummy = UDRn;
}
0
IDLERxD
Sample
(U2X = 0)
Sample
(U2X = 1)
START BIT 0
0 1 2 3 4 5 6 7 8 1 2
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 2 3
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5.17.7.2 Asynchronous Data Recovery
When the receiver clock is synchronized to the start bit, the data recovery can begin. The data recovery unit uses a state
machine that has 16 states for each bit in normal mode and eight states for each bit in double speed mode. Figure 5-74
shows the sampling of the data bits and the parity bit. Each of the samples is given a number that is equal to the state of the
recovery unit.
Figure 5-74. Sampling of Data and Parity Bit
The decision of the logic level of the received bit is taken by doing a majority voting of the logic value to the three samples in
the center of the received bit. The center samples are emphasized on the figure by having the sample number inside boxes.
The majority voting process is done as follows: If two or all three samples have high levels, the received bit is registered to
be a logic 1. If two or all three samples have low levels, the received bit is registered to be a logic 0. This majority voting
process acts as a low pass filter for the incoming signal on the RxDn pin. The recovery process is then repeated until a
complete frame is received. Including the first stop bit. Note that the receiver only uses the first stop bit of a frame.
Figure 5-75 shows the sampling of the stop bit and the earliest possible beginning of the start bit of the next frame.
Figure 5-75. Stop Bit Sampling and Next Start Bit Sampling
The same majority voting is done to the stop bit as done for the other bits in the frame. If the stop bit is registered to have a
logic 0 value, the frame error (FEn) flag will be set.
A new high to low transition indicating the start bit of a new frame can come right after the last of the bits used for majority
voting. For normal speed mode, the first low level sample can be at point marked (A) in Figure 5-75. For double speed mode
the first low level must be delayed to (B). (C) marks a stop bit of full length. The early start bit detection influences the
operational range of the receiver.
RxD
Sample
(U2X = 0)
Sample
(U2X = 1)
Bit n
1 2 3 4 5 6 7 8 1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
RxD
Sample
(U2X = 0)
Sample
(U2X = 1)
STOP 1
1 2 3 4 5 6 0/1
1 2 3 4 5 6 7 8 9 10 0/1 0/1 0/1
(A) (B) (C)
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5.17.7.3 Asynchronous Operational Range
The operational range of the receiver is dependent on the mismatch between the received bit rate and the internally
generated baud rate. If the transmitter is sending frames at too fast or too slow bit rates, or the internally generated baud rate
of the receiver does not have a similar (see Table 5-73) base frequency, the receiver will not be able to synchronize the
frames to the start bit.
The following equations can be used to calculate the ratio of the incoming data rate and internal receiver baud rate.
DSum of character size and parity size (D = 5 to 10 bit)
SSamples per bit. S = 16 for normal speed mode and S = 8 for double speed
mode.
SFFirst sample number used for majority voting. SF = 8 for normal speed and
SF= 4 for double speed mode.
SMMiddle sample number used for majority voting. SM = 9 for normal speed and
SM= 5 for double speed mode.
Rslow is the ratio of the slowest incoming data rate that can be accepted in relation to
the receiver baud rate. Rfast is the ratio of the fastest incoming data rate that can
be accepted in relation to the receiver baud rate.
Table 5-73 and Table 5-74 on page 178 list the maximum receiver baud rate error that can be tolerated. Note that normal
speed mode has higher toleration of baud rate variations.
The recommendations of the maximum receiver baud rate error was made under the assumption that the receiver and
transmitter equally divides the maximum total error.
Table 5-73. Recommended Maximum Receiver Baud Rate Error for Normal Speed Mode (U2Xn = 0)
D
# (Data+Parity Bit) Rslow (%) Rfast (%) Max Total Error (%)
Recommended Max Receiver
Error (%)
593.20 106.67 +6.67/–6.8 ±3.0
694.12 105.79 +5.79/–5.88 ±2.5
794.81 105.11 +5.11/–5.19 ±2.0
895.36 104.58 +4.58/–4.54 ±2.0
995.81 104.14 +4.14/–4.19 ±1.5
10 96.17 103.78 +3.78/–3.83 ±1.5
Table 5-74. Recommended Maximum Receiver Baud Rate Error for Double Speed Mode (U2Xn = 1)
D
# (Data+Parity Bit) Rslow (%) Rfast (%) Max Total Error (%)
Recommended Max Receiver
Error (%)
594.12 105.66 +5.66/–5.88 ±2.5
694.92 104.92 +4.92/–5.08 ±2.0
795.52 104,35 +4.35/–4.48 ±1.5
896.00 103.90 +3.90/–4.00 ±1.5
996.39 103.53 +3.53/–3.61 ±1.5
10 96.70 103.23 +3.23/–3.30 ±1.0
Rslow
D1+()S
S1D+SS
F
+×–
---------------------------------------------
=
Rfast
D2+()S
D1+()SS
M
+
------------------------------------
=
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There are two possible sources for the receivers baud rate error. The receiver’s system clock (XTAL) will always have some
minor instability over the supply voltage range and the temperature range. When using a crystal to generate the system
clock, this is rarely a problem, but for a resonator the system clock may differ more than 2% depending of the resonators
tolerance. The second source for the error is more controllable. The baud rate generator can not always do an exact division
of the system frequency to get the baud rate wanted. In this case an UBRRn value that gives an acceptable low error can be
used if possible.
5.17.8 Multi-processor Communication Mode
Setting the multi-processor communication mode (MPCMn) bit in UCSRnA enables a filtering function of incoming frames
received by the USART receiver. Frames that do not contain address information will be ignored and not put into the receive
buffer. This effectively reduces the number of incoming frames that has to be handled by the CPU, in a system with multiple
MCUs that communicate via the same serial bus. The transmitter is unaffected by the MPCMn setting, but has to be used
differently when it is a part of a system utilizing the multi-processor communication mode.
If the receiver is set up to receive frames that contain 5 to 8 data bits, then the first stop bit indicates if the frame contains
data or address information. If the receiver is set up for frames with nine data bits, then the ninth bit (RXB8n) is used for
identifying address and data frames. When the frame type bit (the first stop or the ninth bit) is one, the frame contains an
address. When the frame type bit is zero the frame is a data frame.
The multi-processor communication mode enables several slave MCUs to receive data from a master MCU. This is done by
first decoding an address frame to find out which MCU has been addressed. If a particular slave MCU has been addressed,
it will receive the following data frames as normal, while the other slave MCUs will ignore the received frames until another
address frame is received.
5.17.8.1 Using MPCMn
For an MCU to act as a master MCU, it can use a 9-bit character frame format (UCSZn = 7). The ninth bit (TXB8n) must be
set when an address frame (TXB8n = 1) or cleared when a data frame (TXB = 0) is being transmitted. The slave MCUs must
in this case be set to use a 9-bit character frame format.
The following procedure should be used to exchange data in multi-processor communication mode:
1. All slave MCUs are in multi-processor communication mode (MPCMn in UCSRnA is set).
2. The master MCU sends an address frame, and all slaves receive and read this frame. In the slave MCUs, the
RXCn flag in UCSRnA will be set as normal.
3. Each slave MCU reads the UDRn register and determines if it has been selected. If so, it clears the MPCMn bit in
UCSRnA, otherwise it waits for the next address byte and keeps the MPCMn setting.
4. The addressed MCU will receive all data frames until a new address frame is received. The other slave MCUs,
which still have the MPCMn bit set, will ignore the data frames.
5. When the last data frame is received by the addressed MCU, the addressed MCU sets the MPCMn bit and waits
for a new address frame from master. The process then repeats from 2.
Using any of the 5- to 8-bit character frame formats is possible, but impractical since the receiver must change between
using n and n+1 character frame formats. This makes full-duplex operation difficult since the transmitter and receiver uses
the same character size setting. If 5- to 8-bit character frames are used, the transmitter must be set to use two stop bit
(USBSn = 1) since the first stop bit is used for indicating the frame type.
Do not use read-modify-write instructions (SBI and CBI) to set or clear the MPCMn bit. The MPCMn bit shares the same I/O
location as the TXCn flag and this might accidentally be cleared when using SBI or CBI instructions.
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5.17.9 USART Register Description
5.17.9.1 USART I/O Data Register n– UDRn
The USART transmit data buffer register and USART receive data buffer registers share the same I/O address referred to as
USART data register or UDRn. The transmit data buffer register (TXB) will be the destination for data written to the UDRn
register location. Reading the UDRn register location will return the contents of the receive data buffer register (RXB).
For 5-, 6-, or 7-bit characters the upper unused bits will be ignored by the transmitter and set to zero by the receiver.
The transmit buffer can only be written when the UDREn flag in the UCSRnA register is set. Data written to UDRn when the
UDREn flag is not set, will be ignored by the USART transmitter. When data is written to the transmit buffer, and the
transmitter is enabled, the transmitter will load the data into the transmit shift register when the shift register is empty. Then
the data will be serially transmitted on the TxDn pin.
The receive buffer consists of a two level FIFO. The FIFO will change its state whenever the receive buffer is accessed. Due
to this behavior of the receive buffer, do not use read-modify-write instructions (SBI and CBI) on this location. Be careful
when using bit test instructions (SBIC and SBIS), since these also will change the state of the FIFO.
5.17.9.2 USART Control and Status Register n A – UCSRnA
• Bit 7 – RXCn: USART Receive Complete
This flag bit is set when there are unread data in the receive buffer and cleared when the receive buffer is empty (i.e., does
not contain any unread data). If the receiver is disabled, the receive buffer will be flushed and consequently the RXCn bit will
become zero. The RXCn flag can be used to generate a receive complete interrupt (see description of the RXCIEn bit).
• Bit 6 – TXCn: USART Transmit Complete
This flag bit is set when the entire frame in the transmit shift register has been shifted out and there are no new data currently
present in the transmit buffer (UDRn). The TXCn flag bit is automatically cleared when a transmit complete interrupt is
executed, or it can be cleared by writing a one to its bit location. The TXCn flag can generate a transmit complete interrupt
(see description of the TXCIEn bit).
• Bit 5 – UDREn: USART Data Register Empty
The UDREn flag indicates if the transmit buffer (UDRn) is ready to receive new data. If UDREn is one, the buffer is empty,
and therefore ready to be written. The UDREn flag can generate a data register empty interrupt (see description of the
UDRIEn bit).
UDREn is set after a reset to indicate that the Transmitter is ready.
• Bit 4 – FEn: Frame Error
This bit is set if the next character in the receive buffer had a frame error when received. I.e., when the first stop bit of the
next character in the receive buffer is zero. This bit is valid until the receive buffer (UDRn) is read. The FEn bit is zero when
the stop bit of received data is one. Always set this bit to zero when writing to UCSRnA.
• Bit 3 – DORn: Data OverRun
This bit is set if a data overrun condition is detected. A data overrun occurs when the receive buffer is full (two characters), it
is a new character waiting in the receive shift register, and a new start bit is detected. This bit is valid until the receive buffer
(UDRn) is read. Always set this bit to zero when writing to UCSRnA.
Bit 76543210
RXB[7:0] UDRn (Read)
TXB[7:0] UDRn (Write)
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
RXCn TXCn UDREn FEn DORn UPEn U2Xn MPCMn UCSRnA
Read/Write R R/W R R R R R/W R/W
Initial Value00100000
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• Bit 2 – UPEn: USART Parity Error
This bit is set if the next character in the receive buffer had a parity error when received and the parity checking was enabled
at that point (UPMn1 = 1). This bit is valid until the receive buffer (UDRn) is read. Always set this bit to zero when writing to
UCSRnA.
• Bit 1 – U2Xn: Double the USART Transmission Speed
This bit only has effect for the asynchronous operation. Write this bit to zero when using synchronous operation.
Writing this bit to one will reduce the divisor of the baud rate divider from 16 to 8 effectively doubling the transfer rate for
asynchronous communication.
• Bit 0 – MPCMn: Multi-processor Communication Mode
This bit enables the Multi-processor Communication mode. When the MPCMn bit is written to one, all the incoming frames
received by the USART receiver that do not contain address information will be ignored. The transmitter is unaffected by the
MPCMn setting. For more detailed information see Section 5.17.8 “Multi-processor Communication Mode” on page 179.
5.17.9.3 USART Control and Status Register n B – UCSRnB
• Bit 7 – RXCIEn: RX Complete Interrupt Enable n
Writing this bit to one enables interrupt on the RXCn flag. A USART receive complete interrupt will be generated only if the
RXCIEn bit is written to one, the global interrupt flag in SREG is written to one and the RXCn bit in UCSRnA is set.
• Bit 6 – TXCIEn: TX Complete Interrupt Enable n
Writing this bit to one enables interrupt on the TXCn flag. A USART transmit complete interrupt will be generated only if the
TXCIEn bit is written to one, the global interrupt flag in SREG is written to one and the TXCn bit in UCSRnA is set.
• Bit 5 – UDRIEn: USART Data Register Empty Interrupt Enable n
Writing this bit to one enables interrupt on the UDREn flag. A data register empty interrupt will be generated only if the
UDRIEn bit is written to one, the global interrupt flag in SREG is written to one and the UDREn bit in UCSRnA is set.
• Bit 4 – RXENn: Receiver Enable n
Writing this bit to one enables the USART receiver. The receiver will override normal port operation for the RxDn pin when
enabled. Disabling the receiver will flush the receive buffer invalidating the FEn, DORn, and UPEn flags.
• Bit 3 – TXENn: Transmitter Enable n
Writing this bit to one enables the USART transmitter. The transmitter will override normal port operation for the TxDn pin
when enabled. The disabling of the transmitter (writing TXENn to zero) will not become effective until ongoing and pending
transmissions are completed, i.e., when the transmit shift register and transmit buffer register do not contain data to be
transmitted. When disabled, the transmitter will no longer override the TxDn port.
• Bit 2 – UCSZn2: Character Size n
The UCSZn2 bits combined with the UCSZn1:0 bit in UCSRnC sets the number of data bits (Character SiZe) in a frame the
receiver and transmitter use.
• Bit 1 – RXB8n: Receive Data Bit 8 n
RXB8n is the ninth data bit of the received character when operating with serial frames with nine data bits. Must be read
before reading the low bits from UDRn.
Bit 76543210
RXCIEn TXCIEn UDRIEn RXENn TXENn UCSZn2 RXB8n TXB8n UCSRnB
Read/Write R/W R/W R/W R/W R/W R/W R R/W
Initial Value 0 0 0 0 0 0 0 0
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• Bit 0 – TXB8n: Transmit Data Bit 8 n
TXB8n is the ninth data bit in the character to be transmitted when operating with serial frames with nine data bits. Must be
written before writing the low bits to UDRn.
5.17.9.4 USART Control and Status Register n C – UCSRnC
• Bits 7:6 – UMSELn1:0 USART Mode Select
These bits select the mode of operation of the USARTn as shown in Table 5-75.
• Bits 5:4 – UPMn1:0: Parity Mode
These bits enable and set type of parity generation and check. If enabled, the transmitter will automatically generate and
send the parity of the transmitted data bits within each frame. The receiver will generate a parity value for the incoming data
and compare it to the UPMn setting. If a mismatch is detected, the UPEn flag in UCSRnA will be set.
• Bit 3 – USBSn: Stop Bit Select
This bit selects the number of stop bits to be inserted by the transmitter. The receiver ignores this setting.
• Bit 2:1 – UCSZn1:0: Character Size
The UCSZn1:0 bits combined with the UCSZn2 bit in UCSRnB sets the number of data bits (Character SiZe) in a frame the
receiver and transmitter use.
Bit 7 6 5 4 3 2 1 0
UMSELn1 UMSELn0 UPMn1 UPMn0 USBSn UCSZn1 UCSZn0 UCPOLn UCSRnC
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 1 1 0
Table 5-75. UMSELn Bits Settings
UMSELn1 UMSELn0 Mode
0 0 Asynchronous USART
0 1 Synchronous USART
1 0 (Reserved)
1 1 Master SPI (MSPIM)(1)
Note: 1. See Section 5.18 “USART in SPI Mode” on page 186 for full description of the Master SPI Mode (MSPIM)
operation
Table 5-76. UPMn Bits Settings
UPMn1 UPMn0 Parity Mode
0 0 Disabled
0 1 Reserved
1 0 Enabled, even parity
1 1 Enabled, odd parity
Table 5-77. USBS Bit Settings
USBSn Stop Bit(s)
01-bit
12-bit
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• Bit 0 – UCPOLn: Clock Polarity
This bit is used for synchronous mode only. Write this bit to zero when asynchronous mode is used. The UCPOLn bit sets
the relationship between data output change and data input sample, and the synchronous clock (XCKn).
5.17.9.5 USART Baud Rate Registers – UBRRnL and UBRRnH
• Bit 15:12 – Reserved Bits
These bits are reserved for future use. For compatibility with future devices, these bit must be written to zero when UBRRnH
is written.
• Bit 11:0 – UBRR11:0: USART Baud Rate Register
This is a 12-bit register which contains the USART baud rate. The UBRRnH contains the four most significant bits, and the
UBRRnL contains the eight least significant bits of the USART baud rate. Ongoing transmissions by the transmitter and
receiver will be corrupted if the baud rate is changed. Writing UBRRnL will trigger an immediate update of the baud rate
prescaler.
5.17.10 Examples of Baud Rate Setting
For standard crystal and resonator frequencies, the most commonly used baud rates for asynchronous operation can be
generated by using the UBRRn settings in Table 5-80 on page 184. UBRRn values which yield an actual baud rate differing
less than 0.5% from the target baud rate, are bold in the table. Higher error ratings are acceptable, but the receiver will have
less noise resistance when the error ratings are high, especially for large serial frames (see Section 5.17.7.3 “Asynchronous
Operational Range” on page 178). The error values are calculated using the following equation:
Table 5-78. UCSZn Bits Settings
UCSZn2 UCSZn1 UCSZn0 Character Size
0 0 0 5-bit
0 0 1 6-bit
0 1 0 7-bit
0 1 1 8-bit
1 0 0 Reserved
1 0 1 Reserved
1 1 0 Reserved
1 1 1 9-bit
Table 5-79. UCPOLn Bit Settings
UCPOLn Transmitted Data Changed (Output of TxDn Pin) Received Data Sampled (Input on RxDn Pin)
0Rising XCKn edge Falling XCKn edge
1Falling XCKn edge Rising XCKn edge
Bit 151413121110 9 8
–––– UBRRn[11:8] UBRRnH
UBRRn[7:0] UBRRnL
76543210
Read/Write RRRRR/WR/WR/WR/W
R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 00000000
00000000
Error %[] BaudRateCloses Match
BaudRate
-------------------------------------------------1–


100%×=
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Table 5-80. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies
Baud
Rate
(bps)
fosc = 1.0000MHz fosc = 1.8432MHz fosc = 2.0000MHz
U2Xn = 0 U2Xn = 1 U2Xn = 0 U2Xn = 1 U2Xn = 0 U2Xn = 1
UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error
2400 25 0.2% 51 0.2% 47 0.0% 95 0.0% 51 0.2% 103 0.2%
4800 12 0.2% 25 0.2% 23 0.0% 47 0.0% 25 0.2% 51 0.2%
9600 6–7.0% 12 0.2% 11 0.0% 23 0.0% 12 0.2% 25 0.2%
14.4k 38.5% 8–3.5% 70.0% 15 0.0% 8–3.5% 16 2.1%
19.2k 28.5% 6–7.0% 50.0% 11 0.0% 6–7.0% 12 0.2%
28.8k 18.5% 38.5% 30.0% 70.0% 38.5% 8–3.5%
38.4k 1–18.6% 28.5% 20.0% 50.0% 28.5% 6–7.0%
57.6k 08.5% 18.5% 10.0% 30.0% 18.5% 38.5%
76.8k ––1–18.6% 1–25.0% 20.0% 1–18.6% 28.5%
115.2k ––08.5% 00.0% 10.0% 08.5% 18.5%
230.4k ––––––00.0% – – – –
250k ––––––––––00.0%
Max.(1) 62.5kbps 125kbps 115.2kbps 230.4kbps 125kbps 250kbps
Note: 1. UBRRn = 0, Error = 0.0%
Table 5-81. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies (Continued)
Baud
Rate
(bps)
fosc = 3.6864MHz fosc = 4.0000MHz fosc = 7.3728MHz
U2Xn = 0 U2Xn = 1 U2Xn = 0 U2Xn = 1 U2Xn = 0 U2Xn = 1
UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error
2400 95 0.0% 191 0.0% 103 0.2% 207 0.2% 191 0.0% 383 0.0%
4800 47 0.0% 95 0.0% 51 0.2% 103 0.2% 95 0.0% 191 0.0%
9600 23 0.0% 47 0.0% 25 0.2% 51 0.2% 47 0.0% 95 0.0%
14.4k 15 0.0% 31 0.0% 16 2.1% 34 –0.8% 31 0.0% 63 0.0%
19.2k 11 0.0% 23 0.0% 12 0.2% 25 0.2% 23 0.0% 47 0.0%
28.8k 70.0% 15 0.0% 8–3.5% 16 2.1% 15 0.0% 31 0.0%
38.4k 50.0% 11 0.0% 6–7.0% 12 0.2% 11 0.0% 23 0.0%
57.6k 30.0% 70.0% 38.5% 8–3.5% 70.0% 15 0.0%
76.8k 20.0% 50.0% 28.5% 6–7.0% 50.0% 11 0.0%
115.2k 10.0% 30.0% 18.5% 38.5% 30.0% 70.0%
230.4k 00.0% 10.0% 08.5% 18.5% 10.0% 30.0%
250k 0–7.8% 1–7.8% 00.0% 10.0% 1–7.8% 3–7.8%
0.5M ––0–7.8% – – 0 0.0% 0–7.8% 1–7.8%
1M ––––––––––0–7.8%
Max.(1) 230.4kbps 460.8kbps 250kbps 0.5Mbps 460.8kbps 921.6kbps
Note: 1. UBRRn = 0, Error = 0.0%
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Table 5-82. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies (Continued)
Baud
Rate
(bps)
fosc = 8.0000MHz fosc = 11.0592MHz fosc = 14.7456MHz
U2Xn = 0 U2Xn = 1 U2Xn = 0 U2Xn = 1 U2Xn = 0 U2Xn = 1
UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error
2400 207 0.2% 416 –0.1% 287 0.0% 575 0.0% 383 0.0% 767 0.0%
4800 103 0.2% 207 0.2% 143 0.0% 287 0.0% 191 0.0% 383 0.0%
9600 51 0.2% 103 0.2% 71 0.0% 143 0.0% 95 0.0% 191 0.0%
14.4k 34 –0.8% 68 0.6% 47 0.0% 95 0.0% 63 0.0% 127 0.0%
19.2k 25 0.2% 51 0.2% 35 0.0% 71 0.0% 47 0.0% 95 0.0%
28.8k 16 2.1% 34 –0.8% 23 0.0% 47 0.0% 31 0.0% 63 0.0%
38.4k 12 0.2% 25 0.2% 17 0.0% 35 0.0% 23 0.0% 47 0.0%
57.6k 8–3.5% 16 2.1% 11 0.0% 23 0.0% 15 0.0% 31 0.0%
76.8k 6–7.0% 12 0.2% 80.0% 17 0.0% 11 0.0% 23 0.0%
115.2k 38.5% 8–3.5% 50.0% 11 0.0% 70.0% 15 0.0%
230.4k 18.5% 38.5% 20.0% 50.0% 30.0% 70.0%
250k 10.0% 30.0% 2–7.8% 5–7.8% 3–7.8% 65.3%
0.5M 00.0% 10.0% – – 2 –7.8% 1–7.8% 3–7.8%
1M ––00.0% ––––0–7.8% 1–7.8%
Max.(1) 0.5Mbps 1Mbps 691.2kbps 1.3824Mbps 921.6kbps 1.8432Mbps
Note: 1. UBRRn = 0, Error = 0.0%
Table 5-83. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies (Continued)
Baud
Rate
(bps)
fosc = 16.0000MHz fosc = 18.4320MHz fosc = 20.0000MHz
U2Xn = 0 U2Xn = 1 U2Xn = 0 U2Xn = 1 U2Xn = 0 U2Xn = 1
UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error
2400 416 –0.1% 832 0.0% 479 0.0% 959 0.0% 520 0.0% 1041 0.0%
4800 207 0.2% 416 –0.1% 239 0.0% 479 0.0% 259 0.2% 520 0.0%
9600 103 0.2% 207 0.2% 119 0.0% 239 0.0% 129 0.2% 259 0.2%
14.4k 68 0.6% 138 –0.1% 79 0.0% 159 0.0% 86 –0.2% 173 –0.2%
19.2k 51 0.2% 103 0.2% 59 0.0% 119 0.0% 64 0.2% 129 0.2%
28.8k 34 –0.8% 68 0.6% 39 0.0% 79 0.0% 42 0.9% 86 –0.2%
38.4k 25 0.2% 51 0.2% 29 0.0% 59 0.0% 32 –1.4% 64 0.2%
57.6k 16 2.1% 34 –0.8% 19 0.0% 39 0.0% 21 –1.4% 42 0.9%
76.8k 12 0.2% 25 0.2% 14 0.0% 29 0.0% 15 1.7% 32 –1.4%
115.2k 8–3.5% 16 2.1% 90.0% 19 0.0% 10 –1.4% 21 –1.4%
230.4k 38.5% 8–3.5% 40.0% 90.0% 48.5% 10 –1.4%
250k 30.0% 70.0% 4–7.8% 82.4% 40.0% 90.0%
0.5M 10.0% 30.0% – – 4 –7.8% – – 4 0.0%
1M 00.0% 10.0% – – – – – – – –
Max.(1) 1Mbps 2Mbps 1.152Mbps 2.304Mbps 1.25Mbps 2.5Mbps
Note: 1. UBRRn = 0, Error = 0.0%
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5.18 USART in SPI Mode
The universal synchronous and asynchronous serial receiver and transmitter (USART) can be set to a master SPI compliant
mode of operation. The master SPI mode (MSPIM) has the following features:
●Full duplex, three-wire synchronous data transfer
●Master operation
●Supports all four SPI modes of operation (mode 0, 1, 2, and 3)
●LSB first or MSB first data transfer (configurable data order)
●Queued operation (double buffered)
●High resolution baud rate generator
●High speed operation (fXCKmax = fCK/2)
●Flexible interrupt generation
5.18.1 Overview
Setting both UMSELn1:0 bits to one enables the USART in MSPIM logic. In this mode of operation the SPI master control
logic takes direct control over the USART resources. These resources include the transmitter and receiver shift register and
buffers, and the baud rate generator. The parity generator and checker, the data and clock recovery logic, and the RX and
TX control logic is disabled. The USART RX and TX control logic is replaced by a common SPI transfer control logic.
However, the pin control logic and interrupt generation logic is identical in both modes of operation.
The I/O register locations are the same in both modes. However, some of the functionality of the control registers changes
when using MSPIM.
5.18.2 Clock Generation
The clock generation logic generates the base clock for the transmitter and receiver. For USART MSPIM mode of operation
only internal clock generation (i.e. master operation) is supported. The data direction register for the XCKn pin (DDR_XCKn)
must therefore be set to one (i.e. as output) for the USART in MSPIM to operate correctly. Preferably the DDR_XCKn should
be set up before the USART in MSPIM is enabled (i.e. TXENn and RXENn bit set to one).
The internal clock generation used in MSPIM mode is identical to the USART synchronous master mode. The baud rate or
UBRRn setting can therefore be calculated using the same equations (see Table 5-84).
BAUD Baud rate (in bits per second, bps)
fOSC System oscillator clock frequency
UBRRn Contents of the UBRRnH and UBRRnL registers, (0-4095)
Table 5-84. Equations for Calculating Baud Rate Register Setting
Operating Mode Equation for Calculating Baud Rate(1) Equation for Calculating UBRRn Value
Synchronous master mode
Note: 1. The baud rate is defined to be the transfer rate in bit per second (bps)
BAUD fOSC
2 UBRRn 1+()
------------------------------------
=
UBRRn fOSC
2BAUD
--------------------1–=
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5.18.3 SPI Data Modes and Timing
There are four combinations of XCKn (SCK) phase and polarity with respect to serial data, which are determined by control
bits UCPHAn and UCPOLn. The data transfer timing diagrams are shown in Figure 5-76. Data bits are shifted out and
latched in on opposite edges of the XCKn signal, ensuring sufficient time for data signals to stabilize. The UCPOLn and
UCPHAn functionality is summarized in Table 5-85. Note that changing the setting of any of these bits will corrupt all ongoing
communication for both the receiver and transmitter.
Figure 5-76. UCPHAn and UCPOLn Data Transfer Timing Diagrams
5.18.4 Frame Formats
A serial frame for the MSPIM is defined to be one character of 8 data bits. The USART in MSPIM mode has two valid frame
formats:
●8-bit data with MSB first
●8-bit data with LSB first
A frame starts with the least or most significant data bit. Then the next data bits, up to a total of eight, are succeeding, ending
with the most or least significant bit accordingly. When a complete frame is transmitted, a new frame can directly follow it, or
the communication line can be set to an idle (high) state.
The UDORDn bit in UCSRnC sets the frame format used by the USART in MSPIM mode. The receiver and transmitter use
the same setting. Note that changing the setting of any of these bits will corrupt all ongoing communication for both the
receiver and transmitter.
16-bit data transfer can be achieved by writing two data bytes to UDRn. A UART transmit complete interrupt will then signal
that the 16-bit value has been shifted out.
Table 5-85. UCPOLn and UCPHAn Functionality-
UCPOLn UCPHAn SPI Mode Leading Edge Trailing Edge
000Sample (rising) Setup (falling)
011Setup (rising) Sample (falling)
102Sample (falling) Setup (rising)
113Setup (falling) Sample (rising)
XCK
UCPOL=0 UCPOL=1
UCPHA=1UCPHA=0
Data setup (TXD)
Data sample (RXD)
XCK
Data setup (TXD)
Data sample (RXD)
XCK
Data setup (TXD)
Data sample (RXD)
XCK
Data setup (TXD)
Data sample (RXD)
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5.18.4.1 USART MSPIM Initialization
The USART in MSPIM mode has to be initialized before any communication can take place. The initialization process
normally consists of setting the baud rate, setting master mode of operation (by setting DDR_XCKn to one), setting frame
format and enabling the transmitter and the receiver. Only the transmitter can operate independently. For interrupt driven
USART operation, the global interrupt flag should be cleared (and thus interrupts globally disabled) when doing the
initialization.
Note: To ensure immediate initialization of the XCKn output the baud-rate register (UBRRn) must be zero at the time
the transmitter is enabled. Contrary to the normal mode USART operation the UBRRn must then be written to
the desired value after the transmitter is enabled, but before the first transmission is started. Setting UBRRn to
zero before enabling the transmitter is not necessary if the initialization is done immediately after a reset since
UBRRn is reset to zero.
Before doing a re-initialization with changed baud rate, data mode, or frame format, be sure that there is no ongoing
transmissions during the period the registers are changed. The TXCn flag can be used to check that the transmitter has
completed all transfers, and the RXCn flag can be used to check that there are no unread data in the receive buffer. Note
that the TXCn flag must be cleared before each transmission (before UDRn is written) if it is used for this purpose.
The following simple USART initialization code examples show one assembly and one C function that are equal in
functionality. The examples assume polling (no interrupts enabled). The baud rate is given as a function parameter. For the
assembly code, the baud rate parameter is assumed to be stored in the r17:r16 registers.
Assembly Code Example(1)
USART_Init:
clr r18
out UBRRnH,r18
out UBRRnL,r18
; Setting the XCKn port pin as output, enables master mode.
sbi XCKn_DDR, XCKn
; Set MSPI mode of operation and SPI data mode 0.
ldi r18, (1<<UMSELn1)|(1<<UMSELn0)|(0<<UCPHAn)|(0<<UCPOLn)
out UCSRnC,r18
; Enable receiver and transmitter.
ldi r18, (1<<RXENn)|(1<<TXENn)
out UCSRnB,r18
; Set baud rate.
; IMPORTANT: The Baud Rate must be set after the transmitter is enabled!
out UBRRnH, r17
out UBRRnL, r18
ret
C Code Example(1)
void USART_Init(unsigned int baud)
{
UBRRn = 0;
/* Setting the XCKn port pin as output, enables master mode. */
XCKn_DDR |= (1<<XCKn);
/* Set MSPI mode of operation and SPI data mode 0. */
UCSRnC = (1<<UMSELn1)|(1<<UMSELn0)|(0<<UCPHAn)|(0<<UCPOLn);
/* Enable receiver and transmitter. */
UCSRnB = (1<<RXENn)|(1<<TXENn);
/* Set baud rate. */
/* IMPORTANT: The Baud Rate must be set after the transmitter is enabled
*/
UBRRn = baud;
}
Note: 1. The example code assumes that the part specific header file is included. For I/O registers located in
extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must be replaced with
instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with “SBRS”,
“SBRC”, “SBR”, and “CBR”.
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5.18.5 Data Transfer
Using the USART in MSPI mode requires the transmitter to be enabled, i.e. the TXENn bit in the UCSRnB register is set to
one. When the transmitter is enabled, the normal port operation of the TxDn pin is overridden and given the function as the
transmitter's serial output. Enabling the receiver is optional and is done by setting the RXENn bit in the UCSRnB register to
one. When the receiver is enabled, the normal pin operation of the RxDn pin is overridden and given the function as the
Receiver's serial input. The XCKn will in both cases be used as the transfer clock.
After initialization the USART is ready for doing data transfers. A data transfer is initiated by writing to the UDRn I/O location.
This is the case for both sending and receiving data since the transmitter controls the transfer clock. The data written to
UDRn is moved from the transmit buffer to the shift register when the shift register is ready to send a new frame.
Note: To keep the input buffer in sync with the number of data bytes transmitted, the UDRn register must be read
once for each byte transmitted. The input buffer operation is identical to normal USART mode, i.e. if an
overflow occurs the character last received will be lost, not the first data in the buffer. This means that if four
bytes are transferred, byte 1 first, then byte 2, 3, and 4, and the UDRn is not read before all transfers are
completed, then byte 3 to be received will be lost, and not byte 1.
The following code examples show a simple USART in MSPIM mode transfer function based on polling of the data register
empty (UDREn) flag and the receive complete (RXCn) flag. The USART has to be initialized before the function can be used.
For the assembly code, the data to be sent is assumed to be stored in register R16 and the data received will be available in
the same register (R16) after the function returns.
The function simply waits for the transmit buffer to be empty by checking the UDREn flag, before loading it with new data to
be transmitted. The function then waits for data to be present in the receive buffer by checking the RXCn flag, before reading
the buffer and returning the value.
Assembly Code Example(1)
USART_MSPIM_Transfer:
; Wait for empty transmit buffer
sbis UCSRnA, UDREn
rjmp USART_MSPIM_Transfer
; Put data (r16) into buffer, sends the data
out UDRn,r16
; Wait for data to be received
USART_MSPIM_Wait_RXCn:
sbis UCSRnA, RXCn
rjmp USART_MSPIM_Wait_RXCn
; Get and return received data from buffer
in r16, UDRn
ret
C Code Example(1)
unsigned char USART_Receive(void)
{
/* Wait for empty transmit buffer */
while (!(UCSRnA & (1<<UDREn)));
/* Put data into buffer, sends the data */
UDRn = data;
/* Wait for data to be received */
while (!(UCSRnA & (1<<RXCn)));
/* Get and return received data from buffer */
return UDRn;
}
Note: 1. The example code assumes that the part specific header file is included. For I/O registers
located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions
must be replaced with instructions that allow access to extended I/O. Typically “LDS” and
“STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
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5.18.5.1 Transmitter and Receiver Flags and Interrupts
The RXCn, TXCn, and UDREn flags and corresponding interrupts in USART in MSPIM mode are identical in function to the
normal USART operation. However, the receiver error status flags (FE, DOR, and PE) are not in use and is always read as
zero.
5.18.5.2 Disabling the Transmitter or Receiver
The disabling of the transmitter or receiver in USART in MSPIM mode is identical in function to the normal USART operation.
5.18.6 USART MSPIM Register Description
The following section describes the registers used for SPI operation using the USART.
5.18.6.1 USART MSPIM I/O Data Register - UDRn
The function and bit description of the USART data register (UDRn) in MSPI mode is identical to normal USART operation
(see Section 5.17.9.1 “USART I/O Data Register n– UDRn” on page 180).
5.18.6.2 USART MSPIM Control and Status Register n A - UCSRnA
• Bit 7 - RXCn: USART Receive Complete
This flag bit is set when there are unread data in the receive buffer and cleared when the receive buffer is empty (i.e., does
not contain any unread data). If the receiver is disabled, the receive buffer will be flushed and consequently the RXCn bit will
become zero. The RXCn flag can be used to generate a receive complete interrupt (see description of the RXCIEn bit).
• Bit 6 - TXCn: USART Transmit Complete
This flag bit is set when the entire frame in the transmit shift register has been shifted out and there are no new data currently
present in the transmit buffer (UDRn). The TXCn flag bit is automatically cleared when a transmit complete interrupt is
executed, or it can be cleared by writing a one to its bit location. The TXCn flag can generate a transmit complete interrupt
(see description of the TXCIEn bit).
• Bit 5 - UDREn: USART Data Register Empty
The UDREn flag indicates if the transmit buffer (UDRn) is ready to receive new data. If UDREn is one, the buffer is empty,
and therefore ready to be written. The UDREn flag can generate a data register empty interrupt (see description of the
UDRIE bit). UDREn is set after a reset to indicate that the transmitter is ready.
• Bit 4:0 - Reserved Bits in MSPI mode
When in MSPI mode, these bits are reserved for future use. For compatibility with future devices, these bits must be written
to zero when UCSRnA is written.
5.18.6.3 USART MSPIM Control and Status Register n B - UCSRnB
• Bit 7 - RXCIEn: RX Complete Interrupt Enable
Writing this bit to one enables interrupt on the RXCn flag. A USART receive complete interrupt will be generated only if the
RXCIEn bit is written to one, the global interrupt flag in SREG is written to one and the RXCn bit in UCSRnA is set.
Bit 7 6 5 4 3 2 1 0
RXCn TXCn UDREn - - - - - UCSRnA
Read/Write R/W R/W R/W R R R R R
Initial Value 0 0 0 0 0 1 1 0
Bit 7 6543210
RXCIEn TXCIEn UDRIE RXENn TXENn - - - UCSRnB
Read/Write R/W R/W R/W R/W R/W R R R
Initial Value 0 0 0 0 0 1 1 0
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• Bit 6 - TXCIEn: TX Complete Interrupt Enable
Writing this bit to one enables interrupt on the TXCn flag. A USART transmit complete interrupt will be generated only if the
TXCIEn bit is written to one, the global interrupt flag in SREG is written to one and the TXCn bit in UCSRnA is set.
• Bit 5 - UDRIE: USART Data Register Empty Interrupt Enable
Writing this bit to one enables interrupt on the UDREn flag. A data register empty interrupt will be generated only if the
UDRIE bit is written to one, the global interrupt flag in SREG is written to one and the UDREn bit in UCSRnA is set.
• Bit 4 - RXENn: Receiver Enable
Writing this bit to one enables the USART receiver in MSPIM mode. The receiver will override normal port operation for the
RxDn pin when enabled. Disabling the receiver will flush the receive buffer. Only enabling the receiver in MSPI mode (i.e.
setting RXENn=1 and TXENn=0) has no meaning since it is the transmitter that controls the transfer clock and since only
master mode is supported.
• Bit 3 - TXENn: Transmitter Enable
Writing this bit to one enables the USART transmitter. The transmitter will override normal port operation for the TxDn pin
when enabled. The disabling of the transmitter (writing TXENn to zero) will not become effective until ongoing and pending
transmissions are completed, i.e., when the transmit shift register and transmit buffer register do not contain data to be
transmitted. When disabled, the transmitter will no longer override the TxDn port.
• Bit 2:0 - Reserved Bits in MSPI mode
When in MSPI mode, these bits are reserved for future use. For compatibility with future devices, these bits must be written
to zero when UCSRnB is written.
5.18.6.4 USART MSPIM Control and Status Register n C - UCSRnC
• Bit 7:6 - UMSELn1:0: USART Mode Select
These bits select the mode of operation of the USART as shown in Table 5-86. See Section 5.17.9.4 “USART Control and
Status Register n C – UCSRnC” on page 182 for full description of the normal USART operation. The MSPIM is enabled
when both UMSELn bits are set to one. The UDORDn, UCPHAn, and UCPOLn can be set in the same write operation where
the MSPIM is enabled.
• Bit 5:3 - Reserved Bits in MSPI mode
When in MSPI mode, these bits are reserved for future use. For compatibility with future devices, these bits must be written
to zero when UCSRnC is written.
• Bit 2 - UDORDn: Data Order
When set to one the LSB of the data word is transmitted first. When set to zero the MSB of the data word is transmitted first.
Refer to the Section 5.17.3 “Frame Formats” on page 168 for details.
Bit 7 6 543 2 1 0
UMSELn1 UMSELn0 - - - UDORDn UCPHAn UCPOLn UCSRnC
Read/Write R/W R/W R R R R/W R/W R/W
Initial Value 0 0 0 0 0 1 1 0
Table 5-86. UMSELn Bits Settings
UMSELn1 UMSELn0 Mode
0 0 Asynchronous USART
0 1 Synchronous USART
1 0 (Reserved)
1 1 Master SPI (MSPIM)
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• Bit 1 - UCPHAn: Clock Phase
The UCPHAn bit setting determine if data is sampled on the leasing edge (first) or tailing (last) edge of XCKn. Refer to the
section Section 5.18.3 “SPI Data Modes and Timing” on page 187 for details.
• Bit 0 - UCPOLn: Clock Polarity
The UCPOLn bit sets the polarity of the XCKn clock. The combination of the UCPOLn and UCPHAn bit settings determine
the timing of the data transfer. Refer to the section Section 5.18.3 “SPI Data Modes and Timing” on page 187 for details.
USART MSPIM baud rate registers - UBRRnL and UBRRnH
The function and bit description of the baud rate registers in MSPI mode is identical to normal USART operation (see Section
5.17.9.5 “USART Baud Rate Registers – UBRRnL and UBRRnH” on page 183).
5.18.7 AVR USART MSPIM versus AVR SPI
The USART in MSPIM mode is fully compatible with the AVR® SPI regarding:
●Master mode timing diagram.
●The UCPOLn bit functionality is identical to the SPI CPOL bit.
●The UCPHAn bit functionality is identical to the SPI CPHA bit.
●The UDORDn bit functionality is identical to the SPI DORD bit.
However, since the USART in MSPIM mode reuses the USART resources, the use of the USART in MSPIM mode is
somewhat different compared to the SPI. In addition to differences of the control register bits, and that only master operation
is supported by the USART in MSPIM mode, the following features differ between the two modules:
●The USART in MSPIM mode includes (double) buffering of the transmitter. The SPI has no buffer.
●The USART in MSPIM mode receiver includes an additional buffer level.
●The SPI WCOL (Write Collision) bit is not included in USART in MSPIM mode.
●The SPI double speed mode (SPI2X) bit is not included. However, the same effect is achieved by setting UBRRn
accordingly.
●Interrupt timing is not compatible.
●Pin control differs due to the master only operation of the USART in MSPIM mode.
A comparison of the USART in MSPIM mode and the SPI pins is shown in Table 5-87.
Table 5-87. Comparison of USART in MSPIM Mode and SPI Pins.
USART_MSPIM SPI Comment
TxDn MOSI Master out only
RxDn MISO Master in only
XCKn SCK (Functionally identical)
(N/A) SS Not supported by USART in MSPIM
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5.19 2-wire Serial Interface
5.19.1 Features
●Simple yet powerful and flexible communication interface, only two bus lines needed
●Both master and slave operation supported
●Device can operate as transmitter or receiver
●7-bit Address space allows up to 128 different slave addresses
●Multi-master arbitration support
●Up to 400kHz data transfer speed
●Slew-rate limited output drivers
●Noise suppression circuitry rejects spikes on bus lines
●Fully programmable slave address with general call support
●Address recognition causes wake-up When AVR is in sleep mode
5.19.2 2-wire Serial Interface Bus Definition
The 2-wire serial interface (TWI) is ideally suited for typical microcontroller applications. The TWI protocol allows the
systems designer to interconnect up to 128 different devices using only two bi-directional bus lines, one for clock (SCL) and
one for data (SDA). The only external hardware needed to implement the bus is a single pull-up resistor for each of the TWI
bus lines. All devices connected to the bus have individual addresses, and mechanisms for resolving bus contention are
inherent in the TWI protocol.
Figure 5-77. TWI Bus Interconnection
5.19.2.1 TWI Terminology
The following definitions are frequently encountered in this section.
The PRTWI bit in Section 5.7.7.1 “Power Reduction Register - PRR” on page 58 must be written to zero to enable the 2-wire
serial interface.
Device 1
SDA
SCL
VCC
Device 2 Device 3 Device n........ R1 R2
Table 5-88. TWI Terminology
Term Description
Master The device that initiates and terminates a transmission. The master also generates the SCL clock.
Slave The device addressed by a Master.
Transmitter The device placing data on the bus.
Receiver The device reading data from the bus.
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5.19.2.2 Electrical Interconnection
As depicted in Figure 5-77 on page 193, both bus lines are connected to the positive supply voltage through pull-up
resistors. The bus drivers of all TWI-compliant devices are open-drain or open-collector. This implements a wired-AND
function which is essential to the operation of the interface. A low level on a TWI bus line is generated when one or more TWI
devices output a zero. A high level is output when all TWI devices tri-state their outputs, allowing the pull-up resistors to pull
the line high. Note that all AVR® devices connected to the TWI bus must be powered in order to allow any bus operation.
The number of devices that can be connected to the bus is only limited by the bus capacitance limit of 400pF and the 7-bit
slave address space. A detailed specification of the electrical characteristics of the TWI is given in Section 6. “2-wire Serial
Interface Characteristics” on page 276. Two different sets of specifications are presented there, one relevant for bus speeds
below 100kHz, and one valid for bus speeds up to 400kHz.
5.19.3 Data Transfer and Frame Format
5.19.3.1 Transferring Bits
Each data bit transferred on the TWI bus is accompanied by a pulse on the clock line. The level of the data line must be
stable when the clock line is high. The only exception to this rule is for generating start and stop conditions.
Figure 5-78. Data Validity
5.19.3.2 START and STOP Conditions
The master initiates and terminates a data transmission. The transmission is initiated when the master issues a START
condition on the bus, and it is terminated when the master issues a STOP condition. Between a START and a STOP
condition, the bus is considered busy, and no other master should try to seize control of the bus. A special case occurs when
a new START condition is issued between a START and STOP condition. This is referred to as a REPEATED START
condition, and is used when the master wishes to initiate a new transfer without relinquishing control of the bus. After a
REPEATED START, the bus is considered busy until the next STOP. This is identical to the START behavior, and therefore
START is used to describe both START and REPEATED START for the remainder of this datasheet, unless otherwise
noted. As depicted below, START and STOP conditions are signalled by changing the level of the SDA line when the SCL
line is high.
Figure 5-79. START, REPEATED START and STOP Conditions
SDA
SCL
Data Stable
Data Change
Data Stable
SDA
SCL
START START REPEATED STARTSTOP STOP
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5.19.3.3 Address Packet Format
All address packets transmitted on the TWI bus are 9 bits long, consisting of 7 address bits, one READ/WRITE control bit
and an acknowledge bit. If the READ/WRITE bit is set, a read operation is to be performed, otherwise a write operation
should be performed. When a slave recognizes that it is being addressed, it should acknowledge by pulling SDA low in the
ninth SCL (ACK) cycle. If the addressed Slave is busy, or for some other reason can not service the master’s request, the
SDA line should be left high in the ACK clock cycle. The master can then transmit a STOP condition, or a REPEATED
START condition to initiate a new transmission. An address packet consisting of a slave address and a READ or a WRITE
bit is called SLA+R or SLA+W, respectively.
The MSB of the address byte is transmitted first. Slave addresses can freely be allocated by the designer, but the address
0000 000 is reserved for a general call.
When a general call is issued, all slaves should respond by pulling the SDA line low in the ACK cycle. A general call is used
when a master wishes to transmit the same message to several slaves in the system. When the general call address
followed by a Write bit is transmitted on the bus, all slaves set up to acknowledge the general call will pull the SDA line low in
the ack cycle. The following data packets will then be received by all the slaves that acknowledged the general call. Note that
transmitting the general call address followed by a read bit is meaningless, as this would cause contention if several slaves
started transmitting different data.
All addresses of the format 1111 xxx should be reserved for future purposes.
Figure 5-80. Address Packet Format
5.19.3.4 Data Packet Format
All data packets transmitted on the TWI bus are nine bits long, consisting of one data byte and an acknowledge bit. During a
data transfer, the master generates the clock and the START and STOP conditions, while the receiver is responsible for
acknowledging the reception. An acknowledge (ACK) is signalled by the receiver pulling the SDA line low during the ninth
SCL cycle. If the receiver leaves the SDA line high, a NACK is signalled. When the receiver has received the last byte, or for
some reason cannot receive any more bytes, it should inform the transmitter by sending a NACK after the final byte. The
MSB of the data byte is transmitted first.
Figure 5-81. Data Packet Format
SDA
SCL
START
Addr MSB Addr LSB R/W ACK
12 789
Aggregate
SDA
SDA from
Transmitter
SDA from
Receiver
SCL from
Master
Data MSB Data LSB ACK
12 7
Data Byte STOP, REPEATED
START or next
Data Byte
SLA + R/W
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5.19.3.5 Combining Address and Data Packets into a Transmission
A transmission basically consists of a START condition, a SLA+R/W, one or more data packets and a STOP condition. An
empty message, consisting of a START followed by a STOP condition, is illegal. Note that the Wired-ANDing of the SCL line
can be used to implement handshaking between the master and the slave. The slave can extend the SCL low period by
pulling the SCL line low. This is useful if the clock speed set up by the master is too fast for the slave, or the slave needs
extra time for processing between the data transmissions. The slave extending the SCL low period will not affect the SCL
high period, which is determined by the master. As a consequence, the Slave can reduce the TWI data transfer speed by
prolonging the SCL duty cycle.
Figure 5-82 shows a typical data transmission. Note that several data bytes can be transmitted between the SLA+R/W and
the STOP condition, depending on the software protocol implemented by the application software.
Figure 5-82. Typical Data Transmission
5.19.4 Multi-master Bus Systems, Arbitration and Synchronization
The TWI protocol allows bus systems with several masters. Special concerns have been taken in order to ensure that
transmissions will proceed as normal, even if two or more masters initiate a transmission at the same time. Two problems
arise in multi-master systems:
●An algorithm must be implemented allowing only one of the masters to complete the transmission. All other masters
should cease transmission when they discover that they have lost the selection process. This selection process is
called arbitration. When a contending master discovers that it has lost the arbitration process, it should immediately
switch to Slave mode to check whether it is being addressed by the winning master. The fact that multiple masters
have started transmission at the same time should not be detectable to the slaves, i.e. the data being transferred on
the bus must not be corrupted.
●Different masters may use different SCL frequencies. A scheme must be devised to synchronize the serial clocks
from all masters, in order to let the transmission proceed in a lockstep fashion. This will facilitate the arbitration
process.
The wired-ANDing of the bus lines is used to solve both these problems. The serial clocks from all masters will be
wired-ANDed, yielding a combined clock with a high period equal to the one from the master with the shortest high period.
The low period of the combined clock is equal to the low period of the master with the longest low period. Note that all
masters listen to the SCL line, effectively starting to count their SCL high and low time-out periods when the combined SCL
line goes high or low, respectively.
SDA
SCL
STOP
START SLA + R/W Data Byte
Addr MSB Addr LSB Data MSB Data LSB ACKR/W ACK
12 789 12 789
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Figure 5-83. SCL Synchronization Between Multiple Masters
Arbitration is carried out by all masters continuously monitoring the SDA line after outputting data. If the value read from the
SDA line does not match the value the master had output, it has lost the arbitration. Note that a master can only lose
arbitration when it outputs a high SDA value while another master outputs a low value. The losing master should
immediately go to slave mode, checking if it is being addressed by the winning master. The SDA line should be left high, but
losing masters are allowed to generate a clock signal until the end of the current data or address packet. Arbitration will
continue until only one master remains, and this may take many bits. If several masters are trying to address the same slave,
arbitration will continue into the data packet.
Figure 5-84. Arbitration Between Two Masters
Note that arbitration is not allowed between:
●A REPEATED START condition and a data bit.
●A STOP condition and a data bit.
●A REPEATED START and a STOP condition.
It is the user software’s responsibility to ensure that these illegal arbitration conditions never occur. This implies that in
multi-master systems, all data transfers must use the same composition of SLA+R/W and data packets. In other words: All
transmissions must contain the same number of data packets, otherwise the result of the arbitration is undefined.
SCL from
Master A
SCL from
Master B
SCL Bus
Line
Masters Start
Counting Low Period
Masters Start
Counting High Period
TA
low
TA
high
TB
low
TB
high
SDA from
Master A
SDA from
Master B
Synchronized
SCL Line
SDA Line
START Master A Loses
Arbitration, SDAA ≠ SDA
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5.19.5 Overview of the TWI Module
The TWI module is comprised of several submodules, as shown in Figure 5-85. All registers drawn in a thick line are
accessible through the AVR® data bus.
Figure 5-85. Overview of the TWI Module
5.19.5.1 SCL and SDA Pins
These pins interface the AVR TWI with the rest of the MCU system. The output drivers contain a slew-rate limiter in order to
conform to the TWI specification. The input stages contain a spike suppression unit removing spikes shorter than 50ns. Note
that the internal pull-ups in the AVR pads can be enabled by setting the PORT bits corresponding to the SCL and SDA pins,
as explained in the I/O port section. The internal pull-ups can in some systems eliminate the need for external ones.
5.19.5.2 Bit Rate Generator Unit
This unit controls the period of SCL when operating in a master mode. The SCL period is controlled by settings in the TWI Bit
rate register (TWBR) and the prescaler bits in the TWI status register (TWSR). Slave operation does not depend on bit rate
or prescaler settings, but the CPU clock frequency in the slave must be at least 16 times higher than the SCL frequency.
Note that slaves may prolong the SCL low period, thereby reducing the average TWI bus clock period. The SCL frequency is
generated according to the following equation:
●TWBR = Value of the TWI Bit rate register.
●Prescaler value = Value of the prescaler (see Table 5-89 on page 201).
Note: TWBR should be 10 or higher if the TWI operates in Master mode. If TWBR is lower than 10, the master may
produce an incorrect output on SDA and SCL for the reminder of the byte. The problem occurs when operating
the TWI in Master mode, sending Start + SLA + R/W to a slave (a slave does not need to be connected to the
bus for the condition to happen).
START/STOP
Control
Spike
Filter
Slew-rate
Control
Address/Data Shift
Register (TWDR)
Arbitration Detection
Spike Suppression
Bit Rate Register
(TWBR)
Prescaler
Ack
Bus Interface Unit
SCL
Spike
Filter
Slew-rate
Control
SDA
Bit Rate Generator
Address Register
(TWAR)
Address Comparator
Address Match Unit
Status Register
(TWSR)
Control Register
(TWCR)
State Machine and
Status Control
Control Unit
TWI Unit
SCL frequency CPU Clock frequency
16 2 TWBR()Prescaler Value()×+
--------------------------------------------------------------------------------------
=
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5.19.5.3 Bus Interface Unit
This unit contains the data and address shift register (TWDR), a START/STOP controller and arbitration detection hardware.
The TWDR contains the address or data bytes to be transmitted, or the address or data bytes received. In addition to the
8-bit TWDR, the bus interface unit also contains a register containing the (N)ACK bit to be transmitted or received. This
(N)ACK register is not directly accessible by the application software. However, when receiving, it can be set or cleared by
manipulating the TWI control register (TWCR). When in transmitter mode, the value of the received (N)ACK bit can be
determined by the value in the TWSR.
The START/STOP controller is responsible for generation and detection of START, REPEATED START, and STOP
conditions. The START/STOP controller is able to detect START and STOP conditions even when the AVR® MCU is in one
of the sleep modes, enabling the MCU to wake up if addressed by a master.
If the TWI has initiated a transmission as master, the arbitration detection hardware continuously monitors the transmission
trying to determine if arbitration is in process. If the TWI has lost an arbitration, the control unit is informed. Correct action
can then be taken and appropriate status codes generated.
5.19.5.4 Address Match Unit
The address match unit checks if received address bytes match the seven-bit address in the TWI address register (TWAR).
If the TWI general call recognition enable (TWGCE) bit in the TWAR is written to one, all incoming address bits will also be
compared against the general call address. Upon an address match, the control unit is informed, allowing correct action to
be taken. The TWI may or may not acknowledge its address, depending on settings in the TWCR. The address match unit is
able to compare addresses even when the AVR MCU is in sleep mode, enabling the MCU to wake up if addressed by a
Master. If another interrupt (e.g., INT0) occurs during TWI power-down address match and wakes up the CPU, the TWI
aborts operation and return to it’s idle state. If this cause any problems, ensure that TWI address match is the only enabled
interrupt when entering power-down.
5.19.5.5 Control Unit
The control unit monitors the TWI bus and generates responses corresponding to settings in the TWI control register
(TWCR). When an event requiring the attention of the application occurs on the TWI bus, the TWI interrupt flag (TWINT) is
asserted. In the next clock cycle, the TWI status register (TWSR) is updated with a status code identifying the event. The
TWSR only contains relevant status information when the TWI interrupt flag is asserted. At all other times, the TWSR
contains a special status code indicating that no relevant status information is available. As long as the TWINT flag is set, the
SCL line is held low. This allows the application software to complete its tasks before allowing the TWI transmission to
continue.
The TWINT flag is set in the following situations:
●After the TWI has transmitted a START/REPEATED START condition.
●After the TWI has transmitted SLA+R/W.
●After the TWI has transmitted an address byte.
●After the TWI has lost arbitration.
●After the TWI has been addressed by own slave address or general call.
●After the TWI has received a data byte.
●After a STOP or REPEATED START has been received while still addressed as a slave.
●When a bus error has occurred due to an illegal START or STOP condition.
5.19.6 TWI Register Description
5.19.6.1 TWI Bit Rate Register – TWBR
• Bits 7..0 – TWI Bit Rate Register
TWBR selects the division factor for the bit rate generator. The bit rate generator is a frequency divider which generates the
SCL clock frequency in the master modes. See Section 5.19.5.2 “Bit Rate Generator Unit” on page 198 for calculating bit
rates.
Bit 76543210
TWBR7 TWBR6 TWBR5 TWBR4 TWBR3 TWBR2 TWBR1 TWBR0 TWBR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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5.19.6.2 TWI Control Register – TWCR
The TWCR is used to control the operation of the TWI. It is used to enable the TWI, to initiate a master access by applying a
START condition to the bus, to generate a receiver acknowledge, to generate a stop condition, and to control halting of the
bus while the data to be written to the bus are written to the TWDR. It also indicates a write collision if data is attempted
written to TWDR while the register is inaccessible.
• Bit 7 – TWINT: TWI Interrupt Flag
This bit is set by hardware when the TWI has finished its current job and expects application software response. If the I-bit in
SREG and TWIE in TWCR are set, the MCU will jump to the TWI interrupt vector.
While the TWINT flag is set, the SCL low period is stretched. The TWINT flag must be cleared by software by writing a logic
one to it. Note that this flag is not automatically cleared by hardware when executing the interrupt routine. Also note that
clearing this flag starts the operation of the TWI, so all accesses to the TWI address register (TWAR), TWI status register
(TWSR), and TWI data register (TWDR) must be complete before clearing this flag.
• Bit 6 – TWEA: TWI Enable Acknowledge Bit
The TWEA bit controls the generation of the acknowledge pulse. If the TWEA bit is written to one, the ACK pulse is
generated on the TWI bus if the following conditions are met:
The device’s own slave address has been received.
A general call has been received, while the TWGCE bit in the TWAR is set.
A data byte has been received in master receiver or slave receiver mode.
By writing the TWEA bit to zero, the device can be virtually disconnected from the 2-wire serial bus temporarily. Address
recognition can then be resumed by writing the TWEA bit to one again.
• Bit 5 – TWSTA: TWI START Condition Bit
The application writes the TWSTA bit to one when it desires to become a master on the 2-wire serial bus. The TWI hardware
checks if the bus is available, and generates a START condition on the bus if it is free. However, if the bus is not free, the
TWI waits until a STOP condition is detected, and then generates a new START condition to claim the bus master status.
TWSTA must be cleared by software when the START condition has been transmitted.
• Bit 4 – TWSTO: TWI STOP Condition Bit
Writing the TWSTO bit to one in master mode will generate a STOP condition on the 2-wire serial bus. When the STOP
condition is executed on the bus, the TWSTO bit is cleared automatically. In slave mode, setting the TWSTO bit can be used
to recover from an error condition. This will not generate a STOP condition, but the TWI returns to a well-defined
unaddressed slave mode and releases the SCL and SDA lines to a high impedance state.
• Bit 3 – TWWC: TWI Write Collision Flag
The TWWC bit is set when attempting to write to the TWI data register – TWDR when TWINT is low. This flag is cleared by
writing the TWDR register when TWINT is high.
• Bit 2 – TWEN: TWI Enable Bit
The TWEN bit enables TWI operation and activates the TWI interface. When TWEN is written to one, the TWI takes control
over the I/O pins connected to the SCL and SDA pins, enabling the slew-rate limiters and spike filters. If this bit is written to
zero, the TWI is switched off and all TWI transmissions are terminated, regardless of any ongoing operation.
Bit 76543210
TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE TWCR
Read/Write R/W R/W R/W R/W R R/W R R/W
Initial Value00000000
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• Bit 1 – Res: Reserved Bit
This bit is a reserved bit and will always read as zero.
• Bit 0 – TWIE: TWI Interrupt Enable
When this bit is written to one, and the I-bit in SREG is set, the TWI interrupt request will be activated for as long as the
TWINT flag is high.
5.19.6.3 TWI Status Register – TWSR
• Bits 7..3 – TWS: TWI Status
These 5 bits reflect the status of the TWI logic and the 2-wire serial bus. The different status codes are described later in this
section. Note that the value read from TWSR contains both the 5-bit status value and the 2-bit prescaler value. The
application designer should mask the prescaler bits to zero when checking the status bits. This makes status checking
independent of prescaler setting. This approach is used in this datasheet, unless otherwise noted.
• Bit 2 – Res: Reserved Bit
This bit is reserved and will always read as zero.
• Bits 1..0 – TWPS: TWI Prescaler Bits
These bits can be read and written, and control the bit rate prescaler.
To calculate bit rates, see Section 5.19.5.2 “Bit Rate Generator Unit” on page 198. The value of TWPS1..0 is used in the
equation.
5.19.6.4 TWI Data Register – TWDR
In transmit mode, TWDR contains the next byte to be transmitted. In receive mode, the TWDR contains the last byte
received. It is writable while the TWI is not in the process of shifting a byte. This occurs when the TWI interrupt flag (TWINT)
is set by hardware. Note that the data register cannot be initialized by the user before the first interrupt occurs. The data in
TWDR remains stable as long as TWINT is set. While data is shifted out, data on the bus is simultaneously shifted in. TWDR
always contains the last byte present on the bus, except after a wake up from a sleep mode by the TWI interrupt. In this
case, the contents of TWDR is undefined. In the case of a lost bus arbitration, no data is lost in the transition from master to
slave. Handling of the ACK bit is controlled automatically by the TWI logic, the CPU cannot access the ACK bit directly.
• Bits 7..0 – TWD: TWI Data Register
These eight bits constitute the next data byte to be transmitted, or the latest data byte received on the 2-wire serial bus.
Bit 76543210
TWS7 TWS6 TWS5 TWS4 TWS3 – TWPS1 TWPS0 TWSR
Read/Write RRRRRRR/WR/W
Initial Value11111000
Table 5-89. TWI Bit Rate Prescaler
TWPS1 TWPS0 Prescaler Value
0 0 1
0 1 4
1 0 16
1 1 64
Bit 76543210
TWD7 TWD6 TWD5 TWD4 TWD3 TWD2 TWD1 TWD0 TWDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value11111111
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5.19.6.5 TWI (Slave) Address Register – TWAR
The TWAR should be loaded with the 7-bit slave address (in the seven most significant bits of TWAR) to which the TWI will
respond when programmed as a slave transmitter or receiver, and not needed in the master modes. In multi master
systems, TWAR must be set in masters which can be addressed as slaves by other masters.
The LSB of TWAR is used to enable recognition of the general call address (0x00). There is an associated address
comparator that looks for the slave address (or general call address if enabled) in the received serial address. If a match is
found, an interrupt request is generated.
• Bits 7..1 – TWA: TWI (Slave) Address Register
These seven bits constitute the slave address of the TWI unit.
• Bit 0 – TWGCE: TWI General Call Recognition Enable Bit
If set, this bit enables the recognition of a General Call given over the 2-wire Serial Bus.
5.19.6.6 TWI (Slave) Address Mask Register – TWAMR
• Bits 7..1 – TWAM: TWI Address Mask
The TWAMR can be loaded with a 7-bit Slave address mask. Each of the bits in TWAMR can mask (disable) the
corresponding address bits in the TWI address register (TWAR). If the mask bit is set to one then the address match logic
ignores the compare between the incoming address bit and the corresponding bit in TWAR. Figure 5-86 shown the address
match logic in detail.
Figure 5-86. TWI Address Match Logic, Block Diagram
• Bit 0 – Res: Reserved Bit
This bit is an unused bit in the Atmel® ATA6612C/ATA6613C, and will always read as zero.
Bit 76543210
TWA6 TWA5 TWA4 TWA3 TWA2 TWA1 TWA0 TWGCE TWAR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value11111110
Bit 76543210
TWAM[6:0] – TWAMR
Read/Write R/W R/W R/W R/W R/W R/W R/W R
Initial Value00000000
TWAR0
Address
Match
TWAMR0
Address Bit Comparator 6..1
Address Bit Comparator 0
Address
Bit 0
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5.19.7 Using the TWI
The AVR® TWI is byte-oriented and interrupt based. Interrupts are issued after all bus events, like reception of a byte or
transmission of a START condition. Because the TWI is interrupt-based, the application software is free to carry on other
operations during a TWI byte transfer. Note that the TWI interrupt enable (TWIE) bit in TWCR together with the global
interrupt enable bit in SREG allow the application to decide whether or not assertion of the TWINT flag should generate an
interrupt request. If the TWIE bit is cleared, the application must poll the TWINT flag in order to detect actions on the TWI
bus.
When the TWINT flag is asserted, the TWI has finished an operation and awaits application response. In this case, the TWI
status register (TWSR) contains a value indicating the current state of the TWI bus. The application software can then
decide how the TWI should behave in the next TWI bus cycle by manipulating the TWCR and TWDR registers.
Figure 5-87 is a simple example of how the application can interface to the TWI hardware. In this example, a master wishes
to transmit a single data byte to a slave. This description is quite abstract, a more detailed explanation follows later in this
section. A simple code example implementing the desired behavior is also presented.
Figure 5-87. Interfacing the Application to the TWI in a Typical Transmission
1. The first step in a TWI transmission is to transmit a START condition. This is done by writing a specific value into
TWCR, instructing the TWI hardware to transmit a START condition. Which value to write is described later on.
However, it is important that the TWINT bit is set in the value written. Writing a one to TWINT clears the flag. The
TWI will not start any operation as long as the TWINT bit in TWCR is set. Immediately after the application has
cleared TWINT, the TWI will initiate transmission of the START condition.
2. When the START condition has been transmitted, the TWINT flag in TWCR is set, and TWSR is updated with a
status code indicating that the START condition has successfully been sent.
3. The application software should now examine the value of TWSR, to make sure that the START condition was
successfully transmitted. If TWSR indicates otherwise, the application software might take some special action,
like calling an error routine. Assuming that the status code is as expected, the application must load SLA+W into
TWDR. Remember that TWDR is used both for address and data. After TWDR has been loaded with the desired
SLA+W, a specific value must be written to TWCR, instructing the TWI hardware to transmit the SLA+W present in
TWDR. Which value to write is described later on. However, it is important that the TWINT bit is set in the value
written. Writing a one to TWINT clears the flag. The TWI will not start any operation as long as the TWINT bit in
TWCR is set. Immediately after the application has cleared TWINT, the TWI will initiate transmission of the
address packet.
4. When the address packet has been transmitted, the TWINT flag in TWCR is set, and TWSR is updated with a
status code indicating that the address packet has successfully been sent. The status code will also reflect
whether a slave acknowledged the packet or not.
START
TWI
Hardware
Action
Application
Action
TWI bus
Indicates
TWINT set
SLA+W A A STOPData
1. Application
writes to TWCR to
initiate
transmission of
START
2. TWINT set.
Status code indicates
START condition sent
4. TWINT set.
Status code indicates
SLA+W sent,
ACK received
6. TWINT set.
Status code indicates
data sent, ACK received
3. Check TWSR to see if START was
sent. Application loads SLA+W into
TWDR, and loads appropriate control
signals into TWCR, makin sure that
TWINT is written to one,
and TWSTA is written to zero.
5. Check TWSR to see if SLA+W was
sent and ACK received.
Application loads data intoTWDR, and
loads appropriate control signals into
TWCR, makin sure that TWINT is
written to one
7. Check TWSR to see if data was sent
and ACK received.
Application loads appropriate control
signals to send STOP into TWCR,
makin sure that TWINT is
written to one
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5. The application software should now examine the value of TWSR, to make sure that the address packet was
successfully transmitted, and that the value of the ACK bit was as expected. If TWSR indicates otherwise, the
application software might take some special action, like calling an error routine. Assuming that the status code is
as expected, the application must load a data packet into TWDR. Subsequently, a specific value must be written to
TWCR, instructing the TWI hardware to transmit the data packet present in TWDR. Which value to write is
described later on. However, it is important that the TWINT bit is set in the value written. Writing a one to TWINT
clears the flag. The TWI will not start any operation as long as the TWINT bit in TWCR is set. Immediately after the
application has cleared TWINT, the TWI will initiate transmission of the data packet.
6. When the data packet has been transmitted, the TWINT flag in TWCR is set, and TWSR is updated with a status
code indicating that the data packet has successfully been sent. The status code will also reflect whether a slave
acknowledged the packet or not.
7. The application software should now examine the value of TWSR, to make sure that the data packet was
successfully transmitted, and that the value of the ACK bit was as expected. If TWSR indicates otherwise, the
application software might take some special action, like calling an error routine. Assuming that the status code is
as expected, the application must write a specific value to TWCR, instructing the TWI hardware to transmit a
STOP condition. Which value to write is described later on. However, it is important that the TWINT bit is set in the
value written. Writing a one to TWINT clears the flag. The TWI will not start any operation as long as the TWINT bit
in TWCR is set. Immediately after the application has cleared TWINT, the TWI will initiate transmission of the
STOP condition. Note that TWINT is NOT set after a STOP condition has been sent.
Even though this example is simple, it shows the principles involved in all TWI transmissions. These can be summarized as
follows:
●When the TWI has finished an operation and expects application response, the TWINT flag is set. The SCL line is
pulled low until TWINT is cleared.
●When the TWINT flag is set, the user must update all TWI registers with the value relevant for the next TWI bus cycle.
As an example, TWDR must be loaded with the value to be transmitted in the next bus cycle.
●After all TWI register updates and other pending application software tasks have been completed, TWCR is written.
When writing TWCR, the TWINT bit should be set. Writing a one to TWINT clears the flag. The TWI will then
commence executing whatever operation was specified by the TWCR setting.
In the following an assembly and C implementation of the example is given. Note that the code below assumes that several
definitions have been made, for example by using include-files.
Table 5-90. Assembly Code Example
Assembly Code Example C Example Comments
1
ldi r16, (1<<TWINT)|(1<<TWSTA)|
(1<<TWEN)
out TWCR, r16
TWCR = (1<<TWINT)|(1<<TWSTA)|
(1<<TWEN) Send START condition
2
wait1:
in r16,TWCR
sbrs r16,TWINT
rjmp wait1
while (!(TWCR & (1<<TWINT)))
;Wait for TWINT flag set. This
indicates that the START
condition has been transmitted
3
in r16,TWSR
andi r16, 0xF8
cpi r16, START
‘brne ERROR
if ((TWSR & 0xF8) != START)
ERROR();
Check value of TWI status
register. Mask prescaler bits. If
status different from START go
to ERROR
ldi r16, SLA_W
out TWDR, r16
ldi r16, (1<<TWINT) | (1<<TWEN)
out TWCR, r16
TWDR = SLA_W;
TWCR = (1<<TWINT) | (1<<TWEN);
Load SLA_W into TWDR
register. Clear TWINT bit in
TWCR to start transmission of
address
4
wait2:
in r16,TWCR
sbrs r16,TWINT
rjmp wait2
while (!(TWCR & (1<<TWINT)))
;
Wait for TWINT flag set. This
indicates that the SLA+W has
been transmitted, and
ACK/NACK has been received.
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5.19.8 Transmission Modes
The TWI can operate in one of four major modes. These are named master transmitter (MT), master receiver (MR), slave
transmitter (ST) and slave receiver (SR). Several of these modes can be used in the same application. As an example, the
TWI can use MT mode to write data into a TWI EEPROM, MR mode to read the data back from the EEPROM. If other
masters are present in the system, some of these might transmit data to the TWI, and then SR mode would be used. It is the
application software that decides which modes are legal.
The following sections describe each of these modes. Possible status codes are described along with figures detailing data
transmission in each of the modes. These figures contain the following abbreviations:
S: START condition
Rs: REPEATED START condition
R: Read bit (high level at SDA)
W: Write bit (low level at SDA)
A: Acknowledge bit (low level at SDA)
A: Not acknowledge bit (high level at SDA)
Data: 8-bit data byte
P: STOP condition
SLA: Slave Address
In Figure 5-89 on page 208 to Figure 5-95 on page 218, circles are used to indicate that the TWINT flag is set. The numbers
in the circles show the status code held in TWSR, with the prescaler bits masked to zero. At these points, actions must be
taken by the application to continue or complete the TWI transfer. The TWI transfer is suspended until the TWINT flag is
cleared by software.
When the TWINT flag is set, the status code in TWSR is used to determine the appropriate software action. For each status
code, the required software action and details of the following serial transfer are given in Table 5-91 on page 207 to
Table 5-94 on page 217. Note that the prescaler bits are masked to zero in these tables.
5
in r16,TWSR
andi r16, 0xF8
cpi r16, MT_SLA_ACK
brne ERROR
if ((TWSR & 0xF8) != MT_SLA_ACK)
ERROR();
Check value of TWI status
register. Mask prescaler bits. If
status different from
MT_SLA_ACK go to ERROR
ldi r16, DATA
out TWDR, r16
ldi r16, (1<<TWINT) | (1<<TWEN)
out TWCR, r16
TWDR = DATA;
TWCR = (1<<TWINT) | (1<<TWEN); Load DATA into TWDR register.
Clear TWINT bit in TWCR to
start transmission of data
6
wait3:
in r16,TWCR
sbrs r16,TWINT
rjmp wait3
while (!(TWCR & (1<<TWINT)))
;
Wait for TWINT flag set. This
indicates that the DATA has
been transmitted, and
ACK/NACK has been received.
7
in r16,TWSR
andi r16, 0xF8
cpi r16, MT_DATA_ACK
brne ERROR
if ((TWSR & 0xF8) != MT_DATA_ACK)
ERROR();
Check value of TWI status
register. Mask prescaler bits. If
status different from
MT_DATA_ACK go to ERROR
ldi r16, (1<<TWINT)|(1<<TWEN)|
(1<<TWSTO)
out TWCR, r16
TWCR = (1<<TWINT)|(1<<TWEN)|
(1<<TWSTO); Transmit STOP condition
Table 5-90. Assembly Code Example (Continued)
Assembly Code Example C Example Comments
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5.19.8.1 Master Transmitter Mode
In the master transmitter mode, a number of data bytes are transmitted to a slave receiver (see Figure 5-88). In order to
enter a master mode, a START condition must be transmitted. The format of the following address packet determines
whether master transmitter or master receiver mode is to be entered. If SLA+W is transmitted, MT mode is entered, if SLA+R
is transmitted, MR mode is entered. All the status codes mentioned in this section assume that the prescaler bits are zero or
are masked to zero.
Figure 5-88. Data Transfer in Master Transmitter Mode
A START condition is sent by writing the following value to TWCR:
TWEN must be set to enable the 2-wire serial interface, TWSTA must be written to one to transmit a START condition and
TWINT must be written to one to clear the TWINT flag. The TWI will then test the 2-wire serial bus and generate a START
condition as soon as the bus becomes free. After a START condition has been transmitted, the TWINT flag is set by
hardware, and the status code in TWSR will be 0x08 (see Table 5-91 on page 207). In order to enter MT mode, SLA+W must
be transmitted. This is done by writing SLA+W to TWDR. Thereafter the TWINT bit should be cleared (by writing it to one) to
continue the transfer. This is accomplished by writing the following value to TWCR:
When SLA+W have been transmitted and an acknowledgement bit has been received, TWINT is set again and a number of
status codes in TWSR are possible. Possible status codes in master mode are 0x18, 0x20, or 0x38. The appropriate action
to be taken for each of these status codes is detailed in Table 5-91 on page 207.
When SLA+W has been successfully transmitted, a data packet should be transmitted. This is done by writing the data byte
to TWDR. TWDR must only be written when TWINT is high. If not, the access will be discarded, and the write collision bit
(TWWC) will be set in the TWCR register. After updating TWDR, the TWINT bit should be cleared (by writing it to one) to
continue the transfer. This is accomplished by writing the following value to TWCR:
This scheme is repeated until the last byte has been sent and the transfer is ended by generating a STOP condition or a
repeated START condition. A STOP condition is generated by writing the following value to TWCR:
TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN –TWIE
value 1 X10X10 X
TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN –TWIE
value 1 X00X10 X
TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN –TWIE
value 1 X00X10 X
TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN –TWIE
value 1 X01X10 X
Device 1
Master
Transmitter
SDA
SCL
V
CC
Device 3 Device n........ R1 R2
Device 2
Slave
Receiver
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A REPEATED START condition is generated by writing the following value to TWCR:
After a repeated START condition (state 0x10) the 2-wire serial interface can access the same slave again, or a new slave
without transmitting a STOP condition. Repeated START enables the master to switch between slaves, master transmitter
mode and master receiver mode without losing control of the bus.
TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN –TWIE
value 1 X10X10 X
Table 5-91. Status codes for Master Transmitter Mode
Status Code
(TWSR)
Prescaler
Bits
are 0
Status of the 2-wire
Serial Bus and 2-wire
Serial Interface
Hardware
Application Software Response
Next Action Taken by TWI HardwareTo/from TWDR
To TWCR
STA STO TWINT TWEA
0x08 A START condition has
been transmitted
Load SLA+W 001 X SLA+W will be transmitted;
ACK or NOT ACK will be received
0x10
A repeated START
condition has been
transmitted
Load SLA+W or
Load SLA+R
0
0
0
0
1
1
X
X
SLA+W will be transmitted; ACK or NOT
ACK will be received
SLA+R will be transmitted; logic will switch
to master receiver mode
0x18
SLA+W has been
transmitted; ACK has
been received
Load data byte or
No TWDR action or
No TWDR action or
No TWDR action
0
1
0
1
0
0
1
1
1
1
1
1
X
X
X
X
Data byte will be transmitted and ACK or
NOT ACK will be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO flag will be reset
STOP condition followed by a START
condition will be transmitted and TWSTO
flag will be reset
0x20
SLA+W has been
transmitted; NOT ACK
has been received
Load data byte or
No TWDR action or
No TWDR action or
No TWDR action
0
1
0
1
0
0
1
1
1
1
1
1
X
X
X
X
Data byte will be transmitted and ACK or
NOT ACK will be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO flag will be reset
STOP condition followed by a START
condition will be transmitted and TWSTO
flag will be reset
0x28
Data byte has been
transmitted; ACK has
been received
Load data byte or
No TWDR action or
No TWDR action or
No TWDR action
0
1
0
1
0
0
1
1
1
1
1
1
X
X
X
X
Data byte will be transmitted and ACK or
NOT ACK will be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO flag will be reset
STOP condition followed by a START
condition will be transmitted and TWSTO
flag will be reset
0x30
Data byte has been
transmitted; NOT ACK
has been received
Load data byte or
No TWDR action or
No TWDR action or
No TWDR action
0
1
0
1
0
0
1
1
1
1
1
1
X
X
X
X
Data byte will be transmitted and ACK or
NOT ACK will be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO flag will be reset
STOP condition followed by a START
condition will be transmitted and TWSTO
flag will be reset
0x38
Arbitration lost in SLA+W
or data bytes
No TWDR action or
No TWDR action
0
1
0
0
1
1
X
X
2-wire serial bus will be released and not
addressed Slave mode entered
A START condition will be transmitted when
the bus becomes free
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Figure 5-89. Formats and States in the Master Transmitter Mode
S
Successfull
transmission
to a slave
receiver
Next transfer
started with a
repeated start
condition
Not acknowledge
received after the
slave address
Not acknowledge
received after a
data byte
Arbitration lost and
addressed as slave
From master to slave Any number of data bytes
and their associated acknowledge bits
This number (contained in TWSR) corresponds
to a defined state of the 2-wire serial bus.
The prescaler bits are zero or masked to zero
From slave to master
Arbitration lost in slave
address or data byte
SLA W
RSSLA W
AAP
AP R
MR
MT
DATA
ADATA
$08 $18
$20
$38
$28
AP
$30
$38
$10
A or A Other master
continues
$68 $78
n
AOther master
continues
To corresponding
states in slave mode
A or A Other master
continues
$B0
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5.19.8.2 Master Receiver Mode
In the master receiver mode, a number of data bytes are received from a slave transmitter (slave see Figure 5-90). In order
to enter a master mode, a START condition must be transmitted. The format of the following address packet determines
whether master transmitter or master receiver mode is to be entered. If SLA+W is transmitted, MT mode is entered, if SLA+R
is transmitted, MR mode is entered. All the status codes mentioned in this section assume that the prescaler bits are zero or
are masked to zero.
Figure 5-90. Data Transfer in Master Receiver Mode
A START condition is sent by writing the following value to TWCR:
TWEN must be written to one to enable the 2-wire serial interface, TWSTA must be written to one to transmit a START
condition and TWINT must be set to clear the TWINT flag. The TWI will then test the 2-wire serial bus and generate a
START condition as soon as the bus becomes free. After a START condition has been transmitted, the TWINT flag is set by
hardware, and the status code in TWSR will be 0x08 (see Table 5-91 on page 207). In order to enter MR mode, SLA+R must
be transmitted. This is done by writing SLA+R to TWDR. Thereafter the TWINT bit should be cleared (by writing it to one) to
continue the transfer. This is accomplished by writing the following value to TWCR:
When SLA+R have been transmitted and an acknowledgement bit has been received, TWINT is set again and a number of
status codes in TWSR are possible. Possible status codes in master mode are 0x38, 0x40, or 0x48. The appropriate action
to be taken for each of these status codes is detailed in Table 5-92 on page 210. Received data can be read from the TWDR
register when the TWINT flag is set high by hardware. This scheme is repeated until the last byte has been received. After
the last byte has been received, the MR should inform the ST by sending a NACK after the last received data byte. The
transfer is ended by generating a STOP condition or a repeated START condition. A STOP condition is generated by writing
the following value to TWCR:
A REPEATED START condition is generated by writing the following value to TWCR:
TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN –TWIE
value 1 X10X10 X
TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN –TWIE
value 1 X00X10 X
TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN –TWIE
value 1 X01X10 X
TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN –TWIE
value 1 X10X10 X
Device 1
Master
Receiver
SDA
SCL
V
CC
Device 3 Device n........ R1 R2
Device 2
Slave
Transmitter
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After a repeated START condition (state 0x10) the 2-wire serial interface can access the same slave again, or a new slave
without transmitting a STOP condition. Repeated START enables the Master to switch between slaves, master transmitter
mode and master receiver mode without losing control over the bus.
Table 5-92. Status codes for Master Receiver Mode
Status Code
(TWSR)
Prescaler
Bits
are 0
Status of the 2-wire
Serial Bus and 2-wire
Serial Interface
Hardware
Application Software Response
Next Action Taken by TWI HardwareTo/from TWDR
To TWCR
STA STO TWINT TWEA
0x08 A START condition has
been transmitted
Load SLA+R 0 0 1 X SLA+R will be transmitted ACK or NOT
ACK will be received
0x10
A repeated START
condition has been
transmitted
Load SLA+R or
Load SLA+W
0
0
0
0
1
1
X
X
SLA+R will be transmitted ACK or NOT
ACK will be received
SLA+W will be transmitted logic will switch
to master transmitter mode
0x38
Arbitration lost in SLA+R
or NOT ACK bit
No TWDR action or
No TWDR action
0
1
0
0
1
1
X
X
2-wire serial bus will be released and not
addressed slave mode will be entered
A START condition will be transmitted when
the bus becomes free
0x40
SLA+R has been
transmitted; ACK has
been received
No TWDR action or
No TWDR action
0
0
0
0
1
1
0
1
Data byte will be received and NOT ACK
will be returned
Data byte will be received and ACK will be
returned
0x48
SLA+R has been
transmitted; NOT ACK
has been received
No TWDR action or
No TWDR action or
No TWDR action
1
0
1
0
1
1
1
1
1
X
X
X
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO flag will be reset
STOP condition followed by a START
condition will be transmitted and TWSTO
flag will be reset
0x50
Data byte has been
received; ACK has been
returned
Read data byte or
Read data byte
0
0
0
0
1
1
0
1
Data byte will be received and NOT ACK
will be returned
Data byte will be received and ACK will be
returned
0x58
Data byte has been
received; NOT ACK has
been returned
Read data byte or
Read data byte or
Read data byte
1
0
1
0
1
1
1
1
1
X
X
X
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO flag will be reset
STOP condition followed by a START
condition will be transmitted and TWSTO
flag will be reset
211
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Figure 5-91. Formats and States in the Master Receiver Mode
S
Successfull
reception
from a slave
receiver
Next transfer
started with a
repeated start
condition
Not acknowledge
received after the
slave address
Arbitration lost and
addressed as slave
Arbitration lost in slave
address or data byte
From master to slave Any number of data bytes
and their associated acknowledge bits
This number (contained in TWSR) corresponds
to a defined state of the 2-wire serial bus.
The prescaler bits are zero or masked to zero
From slave to master
SLA R
RSSLA R
ADATAAP
AP W
MT
MR
DATA
ADATA
$08 $40
$48
$38
$50 $58
$38
$10
A
A or A Other master
continues
$68 $78
n
AOther master
continues
To corresponding
states in slave mode
A or A Other master
continues
$B0
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5.19.8.3 Slave Receiver Mode
In the slave receiver mode, a number of data bytes are received from a Master Transmitter (see Figure 5-92). All the status
codes mentioned in this section assume that the prescaler bits are zero or are masked to zero.
Figure 5-92. Data Transfer in Slave Receiver Mode
To initiate the slave receiver mode, TWAR and TWCR must be initialized as follows:
The upper 7 bits are the address to which the 2-wire serial interface will respond when addressed by a master. If the LSB is
set, the TWI will respond to the general call address (0x00), otherwise it will ignore the general call address.
TWEN must be written to one to enable the TWI. The TWEA bit must be written to one to enable the acknowledgement of
the device’s own slave address or the general call address. TWSTA and TWSTO must be written to zero.
When TWAR and TWCR have been initialized, the TWI waits until it is addressed by its own slave address (or the general
call address if enabled) followed by the data direction bit. If the direction bit is “0” (write), the TWI will operate in SR mode,
otherwise ST mode is entered. After its own slave address and the write bit have been received, the TWINT flag is set and a
valid status code can be read from TWSR. The status code is used to determine the appropriate software action. The
appropriate action to be taken for each status code is detailed in Table 5-93 on page 213. The slave receiver mode may also
be entered if arbitration is lost while the TWI is in the master mode (see states 0x68 and 0x78).
If the TWEA bit is reset during a transfer, the TWI will return a “Not Acknowledge” (“1”) to SDA after the next received data
byte. This can be used to indicate that the slave is not able to receive any more bytes. While TWEA is zero, the TWI does not
acknowledge its own slave address. However, the 2-wire serial bus is still monitored and address recognition may resume at
any time by setting TWEA. This implies that the TWEA bit may be used to temporarily isolate the TWI from the 2-wire serial
bus.
In all sleep modes other than Idle mode, the clock system to the TWI is turned off. If the TWEA bit is set, the interface can
still acknowledge its own slave address or the general call address by using the 2-wire serial bus clock as a clock source.
The part will then wake up from sleep and the TWI will hold the SCL clock low during the wake up and until the TWINT flag is
cleared (by writing it to one). Further data reception will be carried out as normal, with the AVR® clocks running as normal.
Observe that if the AVR is set up with a long start-up time, the SCL line may be held low for a long time, blocking other data
transmissions.
Note that the 2-wire serial interface data register – TWDR does not reflect the last byte present on the bus when waking up
from these sleep modes.
TWAR TWA6 TWA5 TWA4 TWA3 TWA2 TWA1 TWA0 TWGCE
value Device’s Own Slave Address
TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN –TWIE
value 0100010 X
Device 1
Slave
Receiver
SDA
SCL
V
CC
Device 3 Device n........ R1 R2
Device 2
Master
Transmitter
213
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Table 5-93. Status Codes for Slave Receiver Mode
Status
Code
(TWSR)
Prescaler
Bits
are 0
Status of the 2-wire Serial
Bus and 2-wire Serial
Interface Hardware
Application Software Response
Next Action Taken by TWI HardwareTo/from TWDR
To TWCR
STA STO TWINT TWEA
0x60
Own SLA+W has been
received; ACK has been
returned
No TWDR action or
No TWDR action
X
X
0
0
1
1
0
1
Data byte will be received and NOT ACK
will be returned
Data byte will be received and ACK will be
returned
0x68
Arbitration lost in SLA+R/W
as master; own SLA+W has
been received; ACK has
been returned
No TWDR action or
No TWDR action
X
X
0
0
1
1
0
1
Data byte will be received and NOT ACK
will be returned
Data byte will be received and ACK will be
returned
0x70
General call address has
been received; ACK has
been returned
No TWDR action or
No TWDR action
X
X
0
0
1
1
0
1
Data byte will be received and NOT ACK
will be returned
Data byte will be received and ACK will be
returned
0x78
Arbitration lost in SLA+R/W
as Master; General call
address has been received;
ACK has been returned
No TWDR action or
No TWDR action
X
X
0
0
1
1
0
1
Data byte will be received and NOT ACK
will be returned
Data byte will be received and ACK will be
returned
0x80
Previously addressed with
own SLA+W; data has been
received; ACK has been
returned
Read data byte or
Read data byte
X
X
0
0
1
1
0
1
Data byte will be received and NOT ACK
will be returned
Data byte will be received and ACK will be
returned
0x88
Previously addressed with
own SLA+W; data has been
received; NOT ACK has
been returned
Read data byte or
Read data byte or
Read data byte or
Read data byte
0
0
1
1
0
0
0
0
1
1
1
1
0
1
0
1
Switched to the not addressed slave mode;
no recognition of own SLA or GCA
Switched to the not addressed slave mode;
own SLA will be recognized; GCA will be
recognized if TWGCE = “1”
Switched to the not addressed slave mode;
no recognition of own SLA or GCA; a
START condition will be transmitted when
the bus becomes free
Switched to the not addressed slave mode;
own SLA will be recognized; GCA will be
recognized if TWGCE = “1”; a START
condition will be transmitted when the bus
becomes free
0x90
Previously addressed with
general call; data has been
received; ACK has been
returned
Read data byte or
Read data byte
X
X
0
0
1
1
0
1
Data byte will be received and NOT ACK
will be returned
Data byte will be received and ACK will be
returned
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0x98
Previously addressed with
general call; data has been
received; NOT ACK has
been returned
Read data byte or
Read data byte or
Read data byte or
Read data byte
0
0
1
1
0
0
0
0
1
1
1
1
0
1
0
1
Switched to the not addressed slave mode;
no recognition of own SLA or GCA
Switched to the not addressed slave mode;
own SLA will be recognized; GCA will be
recognized if TWGCE = “1”
Switched to the not addressed slave mode;
no recognition of own SLA or GCA; a
START condition will be transmitted when
the bus becomes free
Switched to the not addressed slave mode;
own SLA will be recognized; GCA will be
recognized if TWGCE = “1”; a START
condition will be transmitted when the bus
becomes free
0xA0
A STOP condition or
repeated START condition
has been received while still
addressed as Slave
No action
0
0
1
1
0
0
0
0
1
1
1
1
0
1
0
1
Switched to the not addressed slave mode;
no recognition of own SLA or GCA
Switched to the not addressed slave mode;
own SLA will be recognized; GCA will be
recognized if TWGCE = “1”
Switched to the not addressed Slave mode;
no recognition of own SLA or GCA; a
START condition will be transmitted when
the bus becomes free
Switched to the not addressed Slave mode;
own SLA will be recognized; GCA will be
recognized if TWGCE = “1”;a START
condition will be transmitted when the bus
becomes free
Table 5-93. Status Codes for Slave Receiver Mode (Continued)
Status
Code
(TWSR)
Prescaler
Bits
are 0
Status of the 2-wire Serial
Bus and 2-wire Serial
Interface Hardware
Application Software Response
Next Action Taken by TWI HardwareTo/from TWDR
To TWCR
STA STO TWINT TWEA
215
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Figure 5-93. Formats and States in the Slave Receiver Mode
S
Reception of the own
slave address and one or
more data bytes. All are
acknowledged
Last data byte received
is not acknowledged
Last data byte received
is not acknowledged
Arbitration lost as master
and addressed as slave
Arbitration lost as master
and as slave by general call
From master to slave Any number of data bytes
and their associated acknowledge bits
This number (contained in TWSR) corresponds
to a defined state of the 2-wire serial bus.
The prescaler bits are zero or masked to zero
From slave to master
SLA W ADATAAP or S
A
DATA
ADATA
$60
$68
$80 $80 $A0
$88
A
P or SA
n
$90 $90 $A0
$98
P or SA
Reception of the general call
address and one or more
data bytes
A
$70
General Call DATAAP or S
A
DATA
$78
A
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5.19.8.4 Slave Transmitter Mode
In the slave transmitter mode, a number of data bytes are transmitted to a master receiver (see Figure 5-94). All the status
codes mentioned in this section assume that the prescaler bits are zero or are masked to zero.
Figure 5-94. Data Transfer in Slave Transmitter Mode
To initiate the slave transmitter mode, TWAR and TWCR must be initialized as follows:
The upper seven bits are the address to which the 2-wire serial interface will respond when addressed by a master. If the
LSB is set, the TWI will respond to the general call address (0x00), otherwise it will ignore the general call address.
TWEN must be written to one to enable the TWI. The TWEA bit must be written to one to enable the acknowledgement of
the device’s own slave address or the general call address. TWSTA and TWSTO must be written to zero.
When TWAR and TWCR have been initialized, the TWI waits until it is addressed by its own slave address (or the general
call address if enabled) followed by the data direction bit. If the direction bit is “1” (read), the TWI will operate in ST mode,
otherwise SR mode is entered. After its own slave address and the write bit have been received, the TWINT flag is set and a
valid status code can be read from TWSR. The status code is used to determine the appropriate software action. The
appropriate action to be taken for each status code is detailed in Table 5-94 on page 217. The slave transmitter mode may
also be entered if arbitration is lost while the TWI is in the master mode (see state 0xB0).
If the TWEA bit is written to zero during a transfer, the TWI will transmit the last byte of the transfer. State 0xC0 or state 0xC8
will be entered, depending on whether the master receiver transmits a NACK or ACK after the final byte. The TWI is
switched to the not addressed Slave mode, and will ignore the master if it continues the transfer. Thus the master receiver
receives all “1” as serial data. state 0xC8 is entered if the master demands additional data bytes (by transmitting ACK), even
though the Slave has transmitted the last byte (TWEA zero and expecting NACK from the master).
While TWEA is zero, the TWI does not respond to its own slave address. However, the 2-wire serial bus is still monitored
and address recognition may resume at any time by setting TWEA. This implies that the TWEA bit may be used to
temporarily isolate the TWI from the 2-wire serial bus.
In all sleep modes other than Idle mode, the clock system to the TWI is turned off. If the TWEA bit is set, the interface can
still acknowledge its own slave address or the general call address by using the 2-wire serial bus clock as a clock source.
The part will then wake up from sleep and the TWI will hold the SCL clock will low during the wake up and until the TWINT
flag is cleared (by writing it to one). Further data transmission will be carried out as normal, with the AVR® clocks running as
normal. Observe that if the AVR is set up with a long start-up time, the SCL line may be held low for a long time, blocking
other data transmissions.
Note that the 2-wire serial Interface data register – TWDR does not reflect the last byte present on the bus when waking up
from these sleep modes.
TWAR TWA6 TWA5 TWA4 TWA3 TWA2 TWA1 TWA0 TWGCE
value Device’s Own Slave Address
TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN –TWIE
value 0100010 X
Device 1
Slave
Transmitter
SDA
VCC
SCL
Device 3 Device n........ R1 R2
Device 2
Master
Receiver
217
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Table 5-94. Status Codes for Slave Transmitter Mode
Status
Code
(TWSR)
Prescaler
Bits
are 0
Status of the 2-wire Serial
Bus and 2-wire Serial
Interface Hardware
Application Software Response
Next Action Taken by TWI HardwareTo/from TWDR
To TWCR
STA STO TWINT TWEA
0xA8
Own SLA+R has been
received; ACK has been
returned
Load data byte or
Load data byte
X
X
0
0
1
1
0
1
Last data byte will be transmitted and
NOT ACK should be received
Data byte will be transmitted and ACK
should be received
0xB0
Arbitration lost in SLA+R/W
as Master; own SLA+R has
been received; ACK has
been returned
Load data byte or
Load data byte
X
X
0
0
1
1
0
1
Last data byte will be transmitted and
NOT ACK should be received
Data byte will be transmitted and ACK
should be received
0xB8
Data byte in TWDR has
been transmitted; ACK has
been received
Load data byte or
Load data byte
X
X
0
0
1
1
0
1
Last data byte will be transmitted and
NOT ACK should be received
Data byte will be transmitted and ACK
should be received
0xC0
Data byte in TWDR has
been transmitted; NOT
ACK has been received
No TWDR action or
No TWDR action or
No TWDR action or
No TWDR action
0
0
1
1
0
0
0
0
1
1
1
1
0
1
0
1
Switched to the not addressed slave
mode; no recognition of own SLA or GCA
Switched to the not addressed Slave
mode; own SLA will be recognized; GCA
will be recognized if TWGCE = “1”
Switched to the not addressed Slave
mode; no recognition of own SLA or GCA;
a START condition will be transmitted
when the bus becomes free
Switched to the not addressed Slave
mode; own SLA will be recognized; GCA
will be recognized if TWGCE = “1”; a
START condition will be transmitted when
the bus becomes free
0xC8
Last data byte in TWDR
has been transmitted
(TWEA = “0”); ACK has
been received
No TWDR action or
No TWDR action or
No TWDR action or
No TWDR action
0
0
1
1
0
0
0
0
1
1
1
1
0
1
0
1
Switched to the not addressed slave
mode; no recognition of own SLA or GCA
Switched to the not addressed slave
mode; own SLA will be recognized; GCA
will be recognized if TWGCE = “1”
Switched to the not addressed Slave
mode; no recognition of own SLA or GCA;
a START condition will be transmitted
when the bus becomes free
Switched to the not addressed slave
mode; own SLA will be recognized; GCA
will be recognized if TWGCE = “1”; a
START condition will be transmitted when
the bus becomes free
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218
Figure 5-95. Formats and States in the Slave Transmitter Mode
5.19.8.5 Miscellaneous States
There are two status codes that do not correspond to a defined TWI state (see Table 5-95).
Status 0xF8 indicates that no relevant information is available because the TWINT flag is not set. This occurs between other
states, and when the TWI is not involved in a serial transfer.
Status 0x00 indicates that a bus error has occurred during a 2-wire serial bus transfer. A bus error occurs when a START or
STOP condition occurs at an illegal position in the format frame. Examples of such illegal positions are during the serial
transfer of an address byte, a data byte, or an acknowledge bit. When a bus error occurs, TWINT is set. To recover from a
bus error, the TWSTO flag must set and TWINT must be cleared by writing a logic one to it. This causes the TWI to enter the
not addressed slave mode and to clear the TWSTO flag (no other bits in TWCR are affected). The SDA and SCL lines are
released, and no STOP condition is transmitted.
S
Reception of the own
slave address and one
or more data bytes
Last data byte transmitted.
Switched to not adressed
slave (TWEA = “0”)
A
rbitration lost as master
and addressed as slave
From master to slave Any number of data bytes
and their associated acknowledge bits
This number (contained in TWSR) corresponds
to a defined state of the 2-wire serial bus.
The prescaler bits are zero or masked to zero
From slave to master
SLA R ADATAAP or S
A
DATA
All 1’s
ADATA
$A8
$B0
$B8 $C0
$C8
A
P or SA
n
Table 5-95. Miscellaneous States
Status Code
(TWSR)
Prescaler
Bits
are 0
Status of the 2-wire
Serial Bus and 2-wire
Serial Interface
Hardware
Application Software Response
Next Action Taken by TWI HardwareTo/from TWDR
To TWCR
STA STO TWINT TWEA
0xF8
No relevant state
information available;
TWINT = “0”
No TWDR action No TWCR action Wait or proceed current transfer
0x00 Bus error due to an illegal
START or STOP condition No TWDR action 0 1 1 X
Only the internal hardware is affected, no
STOP condition is sent on the bus. In all
cases, the bus is released and TWSTO is
cleared.
219
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5.19.8.6 Combining Several TWI Modes
In some cases, several TWI modes must be combined in order to complete the desired action. Consider for example reading
data from a serial EEPROM. Typically, such a transfer involves the following steps:
1. The transfer must be initiated.
2. The EEPROM must be instructed what location should be read.
3. The reading must be performed.
4. The transfer must be finished.
Note that data is transmitted both from master to slave and vice versa. The master must instruct the slave what location it
wants to read, requiring the use of the MT mode. Subsequently, data must be read from the slave, implying the use of the
MR mode. Thus, the transfer direction must be changed. The master must keep control of the bus during all these steps, and
the steps should be carried out as an atomical operation. If this principle is violated in a multi master system, another master
can alter the data pointer in the EEPROM between steps 2 and 3, and the master will read the wrong data location. Such a
change in transfer direction is accomplished by transmitting a REPEATED START between the transmission of the address
byte and reception of the data. After a REPEATED START, the master keeps ownership of the bus. The following figure
shows the flow in this transfer.
Figure 5-96. Combining Several TWI Modes to Access a Serial EEPROM
5.19.9 Multi-master Systems and Arbitration
If multiple masters are connected to the same bus, transmissions may be initiated simultaneously by one or more of them.
The TWI standard ensures that such situations are handled in such a way that one of the masters will be allowed to proceed
with the transfer, and that no data will be lost in the process. An example of an arbitration situation is depicted below, where
two masters are trying to transmit data to a slave receiver.
Figure 5-97. An Arbitration Example
S
S = START P = STOPR
S
= REPEATED START
PR
S
ASLA + W A A AADDRESS
Master Transmitter
Transmitted from master to slave Transmitted from slave to master
Master Receiver
DATASLA + R
Device 1
Master
Transmitter
SDA
SCL
V
CC
Device n........ R1 R2
Device 2
Master
Transmitter
Device 3
Slave
Receiver
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Several different scenarios may arise during arbitration, as described below:
●Two or more masters are performing identical communication with the same slave. In this case, neither the slave nor
any of the masters will know about the bus contention.
●Two or more masters are accessing the same slave with different data or direction bit. In this case, arbitration will
occur, either in the READ/WRITE bit or in the data bits. The masters trying to output a one on SDA while another
master outputs a zero will lose the arbitration. Losing masters will switch to not addressed slave mode or wait until the
bus is free and transmit a new START condition, depending on application software action.
●Two or more masters are accessing different slaves. In this case, arbitration will occur in the SLA bits. Masters trying
to output a one on SDA while another master outputs a zero will lose the arbitration. Masters losing arbitration in SLA
will switch to slave mode to check if they are being addressed by the winning master. If addressed, they will switch to
SR or ST mode, depending on the value of the READ/WRITE bit. If they are not being addressed, they will switch to
not addressed slave mode or wait until the bus is free and transmit a new START condition, depending on application
software action.
This is summarized in Figure 5-98. Possible status values are given in circles.
Figure 5-98. Possible Status Codes Caused by Arbitration
Own
Address/General Call
received
Direction
TWI Bus will be released and not addressed slave mode will be entered
A START condition will be transmitted when the bus becomes free
Data byte will be received and NOT ACK will be returned
Data byte will be received and ACK will be returned
Last data byte will be transmitted and NOT ACK should be received
Data byte will be transmitted and ACK should be received
START SLA
No
Yes
Write
Read
38
68/78
Arbitration lost in SLA Arbitration lost in DATA
DATA STOP
B0
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5.20 Analog Comparator
The analog comparator compares the input values on the positive pin AIN0 and negative pin AIN1. When the voltage on the
positive pin AIN0 is higher than the voltage on the negative pin AIN1, the analog comparator output, ACO, is set. The
comparator’s output can be set to trigger the Timer/Counter1 input capture function. In addition, the comparator can trigger a
separate interrupt, exclusive to the analog comparator. The user can select interrupt triggering on comparator output rise, fall
or toggle. A block diagram of the comparator and its surrounding logic is shown in Figure 5-99.
The power reduction ADC bit, PRADC, in Section 5.7.7.1 “Power Reduction Register - PRR” on page 58 must be disabled by
writing a logical zero to be able to use the ADC input MUX.
Figure 5-99. Analog Comparator Block Diagram(2)
Notes: 1. See Table 5-97 on page 223.
2. Refer to Table 5-38 on page 89 for analog comparator pin placement.
5.20.1 ADC Control and Status Register B – ADCSRB
• Bit 6 – ACME: Analog Comparator Multiplexer Enable
When this bit is written logic one and the ADC is switched off (ADEN in ADCSRA is zero), the ADC multiplexer selects the
negative input to the analog comparator. When this bit is written logic zero, AIN1 is applied to the negative input of the
analog comparator. For a detailed description of this bit (see Section 5.20.3 “Analog Comparator Multiplexed Input” on page
223).
Bandgap
Reference
Interrupt
Select
AIN0
VCC
ACIS1
ADC Multiplexer
Output
(1)
ACIS0 ACIC
ACO
ACIE
Analog
Comparator
IRQ
ACI
To T/C1 Capture
Trigger MUX
ACBG
ACME
ADEN
ACD
+
-
AIN1
Bit 7 6543210
–ACME–––ADTS2 ADTS1 ADTS0 ADCSRB
Read/Write R R/W R R R R/W R/W R/W
Initial Value0 0000000
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5.20.2 Analog Comparator Control and Status Register – ACSR
• Bit 7 – ACD: Analog Comparator Disable
When this bit is written logic one, the power to the analog comparator is switched off. This bit can be set at any time to turn
off the analog comparator. This will reduce power consumption in active and idle mode. When changing the ACD bit, the
analog comparator interrupt must be disabled by clearing the ACIE bit in ACSR. Otherwise an interrupt can occur when the
bit is changed.
• Bit 6 – ACBG: Analog Comparator Bandgap Select
When this bit is set, a fixed bandgap reference voltage replaces the positive input to the analog comparator. When this bit is
cleared, AIN0 is applied to the positive input of the analog comparator (see Section 5.8.8 “Internal Voltage Reference” on
page 65).
• Bit 5 – ACO: Analog Comparator Output
The output of the analog comparator is synchronized and then directly connected to ACO. The synchronization introduces a
delay of 1 - 2 clock cycles.
• Bit 4 – ACI: Analog Comparator Interrupt Flag
This bit is set by hardware when a comparator output event triggers the interrupt mode defined by ACIS1 and ACIS0. The
analog comparator interrupt routine is executed if the ACIE bit is set and the I-bit in SREG is set. ACI is cleared by hardware
when executing the corresponding interrupt handling vector. Alternatively, ACI is cleared by writing a logic one to the flag.
• Bit 3 – ACIE: Analog Comparator Interrupt Enable
When the ACIE bit is written logic one and the I-bit in the status register is set, the analog comparator interrupt is activated.
When written logic zero, the interrupt is disabled.
• Bit 2 – ACIC: Analog Comparator Input Capture Enable
When written logic one, this bit enables the input capture function in Timer/Counter1 to be triggered by the analog
comparator. The comparator output is in this case directly connected to the input capture front-end logic, making the
comparator utilize the noise canceler and edge select features of the Timer/Counter1 input capture interrupt. When written
logic zero, no connection between the analog comparator and the input capture function exists. To make the comparator
trigger the Timer/Counter1 input capture interrupt, the ICIE1 bit in the timer interrupt mask register (TIMSK1) must be set.
• Bits 1, 0 – ACIS1, ACIS0: Analog Comparator Interrupt Mode Select
These bits determine which comparator events that trigger the analog comparator interrupt. The different settings are shown
in Table 5-96 on page 222.
When changing the ACIS1/ACIS0 bits, the analog comparator interrupt must be disabled by clearing its interrupt enable bit in
the ACSR register. Otherwise an interrupt can occur when the bits are changed.
Bit 76543210
ACD ACBG ACO ACI ACIE ACIC ACIS1 ACIS0 ACSR
Read/Write R/W R/W R R/W R/W R/W R/W R/W
Initial Value00N/A00000
Table 5-96. ACIS1/ACIS0 Settings
ACIS1 ACIS0 Interrupt Mode
0 0 Comparator interrupt on output toggle.
0 1 Reserved
1 0 Comparator interrupt on falling output edge.
1 1 Comparator interrupt on rising output edge.
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5.20.3 Analog Comparator Multiplexed Input
It is possible to select any of the ADC7..0 pins to replace the negative input to the analog comparator. The ADC multiplexer
is used to select this input, and consequently, the ADC must be switched off to utilize this feature. If the analog comparator
multiplexer enable bit (ACME in ADCSRB) is set and the ADC is switched off (ADEN in ADCSRA is zero), MUX2..0 in
ADMUX select the input pin to replace the negative input to the analog comparator, as shown in Table 5-97. If ACME is
cleared or ADEN is set, AIN1 is applied to the negative input to the analog comparator.
5.20.3.1 Digital Input Disable Register 1 – DIDR1
• Bit 7..2 – Res: Reserved Bits
These bits are unused bits in the Atmel® ATA6612C/ATA6613C, and will always read as zero.
• Bit 1, 0 – AIN1D, AIN0D: AIN1, AIN0 Digital Input Disable
When this bit is written logic one, the digital input buffer on the AIN1/0 pin is disabled. The corresponding PIN register bit will
always read as zero when this bit is set. When an analog signal is applied to the AIN1/0 pin and the digital input from this pin
is not needed, this bit should be written logic one to reduce power consumption in the digital input buffer.
Table 5-97. Analog Comparator Multiplexed Input
ACME ADEN MUX2..0 Analog Comparator Negative Input
0 x xxx AIN1
1 1 xxx AIN1
1 0 000 ADC0
1 0 001 ADC1
1 0 010 ADC2
1 0 011 ADC3
1 0 100 ADC4
1 0 101 ADC5
1 0 110 ADC6
1 0 111 ADC7
Bit 76543210
––––––AIN1DAIN0DDIDR1
Read/Write RRRRRRR/WR/W
Initial Value00000000
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5.21 Analog-to-Digital Converter
5.21.1 Features
●10-bit resolution
●0.5LSB integral non-linearity
●±2LSB absolute accuracy
●13 - 260µs conversion time
●Up to 15kSPS at maximum resolution
●6 multiplexed single ended input channels
●2 additional multiplexed single ended input channels (TQFP and QFN package only)
●Optional left adjustment for ADC result readout
●0 to VCC ADC input voltage range
●Selectable 1.1V ADC reference voltage
●Free running or single conversion mode
●Interrupt on ADC conversion complete
●Sleep mode noise canceler
The Atmel® ATA6612C/ATA6613C features a 10-bit successive approximation ADC. The ADC is connected to an 8-channel
analog multiplexer which allows eight single-ended voltage inputs constructed from the pins of Port A. The single-ended
voltage inputs refer to 0V (GND).
The ADC contains a sample and hold circuit which ensures that the input voltage to the ADC is held at a constant level
during conversion. A block diagram of the ADC is shown in Figure 5-100 on page 225.
The ADC has a separate analog supply voltage pin, AVCC. AVCC must not differ more than ± 0.3V from VCC. See the
paragraph Section 5.21.5 “ADC Noise Canceler” on page 231 on how to connect this pin.
Internal reference voltages of nominally 1.1V or AVCC are provided On-chip. The voltage reference may be externally
decoupled at the AREF pin by a capacitor for better noise performance.
The power reduction ADC bit, PRADC, in Section 5.7.7.1 “Power Reduction Register - PRR” on page 58 must be disabled by
writing a logical zero to enable the ADC.
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Figure 5-100.Analog to Digital Converter Block Schematic Operation
The ADC converts an analog input voltage to a 10-bit digital value through successive approximation. The minimum value
represents GND and the maximum value represents the voltage on the AREF pin minus 1LSB. Optionally, AVCC or an
internal 1.1V reference voltage may be connected to the AREF pin by writing to the REFSn bits in the ADMUX register. The
internal voltage reference may thus be decoupled by an external capacitor at the AREF pin to improve noise immunity.
The analog input channel is selected by writing to the MUX bits in ADMUX. Any of the ADC input pins, as well as GND and a
fixed bandgap voltage reference, can be selected as single ended inputs to the ADC. The ADC is enabled by setting the
ADC enable bit, ADEN in ADCSRA. Voltage reference and input channel selections will not go into effect until ADEN is set.
The ADC does not consume power when ADEN is cleared, so it is recommended to switch off the ADC before entering
power saving sleep modes.
Prescaler
-
+
15 0
ADC Multiplexer
Select (ADMUX)
MUX Decoder
AVCC
8-bit Data Bus
AREF
GND
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0
10-bit DAC
Input
MUX
Sample and Hold
Comparator
Internal 1.1V
Reference
Conversion Logic
ADC Conversion
Complete IRQ
ADC CTRL and Status
Register (ADCSRA)
ADC Data Register
(ADCH/ADCL)
ADIF
ADEN
REFS1
REFS0
ADLAR
MUX3
MUX2
MUX1
MUX0
Channel Selection
ADSC
ADIF
ADFR
ADPS2
ADPS1
ADPS0
ADIE
Bandgap
Reference
ADC[9:0]
ADC
Multiplexer
Output
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The ADC generates a 10-bit result which is presented in the ADC data registers, ADCH and ADCL. By default, the result is
presented right adjusted, but can optionally be presented left adjusted by setting the ADLAR bit in ADMUX.
If the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read ADCH. Otherwise, ADCL must
be read first, then ADCH, to ensure that the content of the data registers belongs to the same conversion. Once ADCL is
read, ADC access to data registers is blocked. This means that if ADCL has been read, and a conversion completes before
ADCH is read, neither register is updated and the result from the conversion is lost. When ADCH is read, ADC access to the
ADCH and ADCL registers is re-enabled.
The ADC has its own interrupt which can be triggered when a conversion completes. When ADC access to the data registers
is prohibited between reading of ADCH and ADCL, the interrupt will trigger even if the result is lost.
5.21.2 Starting a Conversion
A single conversion is started by disabling the power reduction ADC bit, PRADC, in Section 5.7.7.1 “Power Reduction
Register - PRR” on page 58 by writing a logical zero to it and writing a logical one to the ADC start conversion bit, ADSC.
This bit stays high as long as the conversion is in progress and will be cleared by hardware when the conversion is
completed. If a different data channel is selected while a conversion is in progress, the ADC will finish the current conversion
before performing the channel change.
Alternatively, a conversion can be triggered automatically by various sources. Auto triggering is enabled by setting the ADC
auto trigger enable bit, ADATE in ADCSRA. The trigger source is selected by setting the ADC trigger select bits, ADTS in
ADCSRB (See description of the ADTS bits for a list of the trigger sources). When a positive edge occurs on the selected
trigger signal, the ADC prescaler is reset and a conversion is started. This provides a method of starting conversions at fixed
intervals. If the trigger signal still is set when the conversion completes, a new conversion will not be started. If another
positive edge occurs on the trigger signal during conversion, the edge will be ignored. Note that an interrupt flag will be set
even if the specific interrupt is disabled or the global interrupt enable bit in SREG is cleared. A conversion can thus be
triggered without causing an interrupt. However, the interrupt flag must be cleared in order to trigger a new conversion at the
next interrupt event.
Figure 5-101. ADC Auto Trigger Logic
Using the ADC interrupt flag as a trigger source makes the ADC start a new conversion as soon as the ongoing conversion
has finished. The ADC then operates in free running mode, constantly sampling and updating the ADC data register. The
first conversion must be started by writing a logical one to the ADSC bit in ADCSRA. In this mode the ADC will perform
successive conversions independently of whether the ADC interrupt flag, ADIF is cleared or not.
If auto triggering is enabled, single conversions can be started by writing ADSC in ADCSRA to one. ADSC can also be used
to determine if a conversion is in progress. The ADSC bit will be read as one during a conversion, independently of how the
conversion was started.
Edge
Detector
Conversion
Logic
Prescaler
ADIF
ADSC
ADATE START CLK
ADC
ADTS[2:0]
.
.
.
.
SOURCE 1
SOURCE n
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5.21.3 Prescaling and Conversion Timing
Figure 5-102. ADC Prescaler
By default, the successive approximation circuitry requires an input clock frequency between 50kHz and 200kHz to get
maximum resolution. If a lower resolution than 10bits is needed, the input clock frequency to the ADC can be higher than
200kHz to get a higher sample rate.
The ADC module contains a prescaler, which generates an acceptable ADC clock frequency from any CPU frequency above
100kHz. The prescaling is set by the ADPS bits in ADCSRA. The prescaler starts counting from the moment the ADC is
switched on by setting the ADEN bit in ADCSRA. The prescaler keeps running for as long as the ADEN bit is set, and is
continuously reset when ADEN is low.
When initiating a single ended conversion by setting the ADSC bit in ADCSRA, the conversion starts at the following rising
edge of the ADC clock cycle.
A normal conversion takes 13 ADC clock cycles. The first conversion after the ADC is switched on (ADEN in ADCSRA is set)
takes 25 ADC clock cycles in order to initialize the analog circuitry.
The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conversion and 13.5 ADC clock
cycles after the start of an first conversion. When a conversion is complete, the result is written to the ADC data registers,
and ADIF is set. In single conversion mode, ADSC is cleared simultaneously. The software may then set ADSC again, and a
new conversion will be initiated on the first rising ADC clock edge.
When auto triggering is used, the prescaler is reset when the trigger event occurs. This assures a fixed delay from the trigger
event to the start of conversion. In this mode, the sample-and-hold takes place two ADC clock cycles after the rising edge on
the trigger source signal. Three additional CPU clock cycles are used for synchronization logic.
In free running mode, a new conversion will be started immediately after the conversion completes, while ADSC remains
high. For a summary of conversion times (see Table 5-98 on page 229).
7-bit ADC Prescaler
ADC Clock Source
ADEN
START
CK
IO
ADPS0
ADPS1
ADPS2
Reset
CK/2
CK/4
CK/8
CK/16
CK/32
CK/64
CK/128
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Figure 5-103. ADC Timing Diagram, First Conversion (Single Conversion Mode)
Figure 5-104. ADC Timing Diagram, Single Conversion
1 2 12 13 14 15 16 17 18 19 20 21 22 23 24 25 1 2 3
Cycle Number
First Conversion
Sign and MSB of Result
LSB of Result
Next
Conversion
MUX and REFS
Update
Conversion
Complete MUX and REFS
Update
ADC Clock
ADEN
ADSC
ADIF
ADCH
ADCL
Sample and Hold
12345678910111213 123
Cycle Number
One Conversion
Sign and MSB of Result
LSB of Result
Next Conversion
MUX and REFS
Update
Conversion
Complete MUX and REFS
Update
ADC Clock
ADSC
ADIF
ADCH
ADCL
Sample and Hold
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Figure 5-105. ADC Timing Diagram, Auto Triggered Conversion
Figure 5-106. ADC Timing Diagram, Free Running Conversion
Table 5-98. ADC Conversion Time
Condition
Sample and Hold (Cycles from
Start of Conversion) Conversion Time (Cycles)
First conversion 13.5 25
Normal conversions, single ended 1.5 13
Auto triggered conversions 213.5
12345678910111213 12
Cycle Number
One Conversion
Sign and MSB of Result
LSB of Result
Next Conversion
MUX and REFS
Update
Prescaler
Reset
Prescaler
Reset
Conversion
Complete
ADC Clock
Trigger
Source
ADIF
ADATE
ADCH
ADCL
Sample and Hold
11 12 13 1 2 3 4
Cycle Number
One Conversion
Sign and MSB of Result
LSB of Result
Next Conversion
MUX and REFS
Update
Conversion
Complete
ADC Clock
ADSC
ADIF
ADCH
ADCL
Sample and Hold
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5.21.4 Changing Channel or Reference Selection
The MUXn and REFS1:0 bits in the ADMUX register are single buffered through a temporary register to which the CPU has
random access. This ensures that the channels and reference selection only takes place at a safe point during the
conversion. The channel and reference selection is continuously updated until a conversion is started. Once the conversion
starts, the channel and reference selection is locked to ensure a sufficient sampling time for the ADC. Continuous updating
resumes in the last ADC clock cycle before the conversion completes (ADIF in ADCSRA is set). Note that the conversion
starts on the following rising ADC clock edge after ADSC is written. The user is thus advised not to write new channel or
reference selection values to ADMUX until one ADC clock cycle after ADSC is written.
If auto triggering is used, the exact time of the triggering event can be indeterministic. Special care must be taken when
updating the ADMUX register, in order to control which conversion will be affected by the new settings.
If both ADATE and ADEN is written to one, an interrupt event can occur at any time. If the ADMUX register is changed in this
period, the user cannot tell if the next conversion is based on the old or the new settings. ADMUX can be safely updated in
the following ways:
a. When ADATE or ADEN is cleared.
b. During conversion, minimum one ADC clock cycle after the trigger event.
c. After a conversion, before the Interrupt Flag used as trigger source is cleared.
When updating ADMUX in one of these conditions, the new settings will affect the next ADC conversion.
5.21.4.1 ADC Input Channels
When changing channel selections, the user should observe the following guidelines to ensure that the correct channel is
selected:
In Single Conversion mode, always select the channel before starting the conversion. The channel selection may be
changed one ADC clock cycle after writing one to ADSC. However, the simplest method is to wait for the conversion to
complete before changing the channel selection.
In free running mode, always select the channel before starting the first conversion. The channel selection may be changed
one ADC clock cycle after writing one to ADSC. However, the simplest method is to wait for the first conversion to complete,
and then change the channel selection. Since the next conversion has already started automatically, the next result will
reflect the previous channel selection. Subsequent conversions will reflect the new channel selection.
5.21.4.2 ADC Voltage Reference
The reference voltage for the ADC (VREF) indicates the conversion range for the ADC. Single ended channels that exceed
VREF will result in codes close to 0x3FF. VREF can be selected as either AVCC, internal 1.1V reference, or external AREF pin.
AVCC is connected to the ADC through a passive switch. The internal 1.1V reference is generated from the internal bandgap
reference (VBG) through an internal amplifier. In either case, the external AREF pin is directly connected to the ADC, and the
reference voltage can be made more immune to noise by connecting a capacitor between the AREF pin and ground. VREF
can also be measured at the AREF pin with a high impedant voltmeter. Note that VREF is a high impedant source, and only a
capacitive load should be connected in a system.
If the user has a fixed voltage source connected to the AREF pin, the user may not use the other reference voltage options
in the application, as they will be shorted to the external voltage. If no external voltage is applied to the AREF pin, the user
may switch between AVCC and 1.1V as reference selection. The first ADC conversion result after switching reference voltage
source may be inaccurate, and the user is advised to discard this result.
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5.21.5 ADC Noise Canceler
The ADC features a noise canceler that enables conversion during sleep mode to reduce noise induced from the CPU core
and other I/O peripherals. The noise canceler can be used with ADC noise reduction and Idle mode. To make use of this
feature, the following procedure should be used:
a. Make sure that the ADC is enabled and is not busy converting. Single conversion mode must be selected and the
ADC conversion complete interrupt must be enabled.
b. Enter ADC noise reduction mode (or idle mode). The ADC will start a conversion once the CPU has been halted.
c. If no other interrupts occur before the ADC conversion completes, the ADC interrupt will wake up the CPU and
execute the ADC conversion complete interrupt routine. If another interrupt wakes up the CPU before the ADC
conversion is complete, that interrupt will be executed, and an ADC conversion complete interrupt request will be
generated when the ADC conversion completes. The CPU will remain in active mode until a new sleep command
is executed.
Note that the ADC will not be automatically turned off when entering other sleep modes than idle mode and ADC noise
reduction mode. The user is advised to write zero to ADEN before entering such sleep modes to avoid excessive power
consumption.
5.21.5.1 Analog Input Circuitry
The analog input circuitry for single ended channels is illustrated in Figure 5-107 An analog source applied to ADCn is
subjected to the pin capacitance and input leakage of that pin, regardless of whether that channel is selected as input for the
ADC. When the channel is selected, the source must drive the S/H capacitor through the series resistance (combined
resistance in the input path).
The ADC is optimized for analog signals with an output impedance of approximately 10 kΩ or less. If such a source is used,
the sampling time will be negligible. If a source with higher impedance is used, the sampling time will depend on how long
time the source needs to charge the S/H capacitor, with can vary widely. The user is recommended to only use low impedant
sources with slowly varying signals, since this minimizes the required charge transfer to the S/H capacitor.
Signal components higher than the nyquist frequency (fADC/2) should not be present for either kind of channels, to avoid
distortion from unpredictable signal convolution. The user is advised to remove high frequency components with a low-pass
filter before applying the signals as inputs to the ADC.
Figure 5-107. Analog Input Circuitry
IIL
VCC/2
CS/H = 14pF
IIH
A
DCn
1 to 100kΩ
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5.21.5.2 Analog Noise Canceling Techniques
Digital circuitry inside and outside the device generates EMI which might affect the accuracy of analog measurements. If
conversion accuracy is critical, the noise level can be reduced by applying the following techniques:
a. Keep analog signal paths as short as possible. Make sure analog tracks run over the analog ground plane, and
keep them well away from high-speed switching digital tracks.
b. The AVCC pin on the device should be connected to the digital VCC supply voltage via an LC network as shown in
Figure 5-108.
c. Use the ADC noise canceler function to reduce induced noise from the CPU.
d. If any ADC [3..0] port pins are used as digital outputs, it is essential that these do not switch while a conversion is
in progress. However, using the 2-wire interface (ADC4 and ADC5) will only affect the conversion on ADC4 and
ADC5 and not the other ADC channels.
Figure 5-108. ADC Power Connections
GND
VCC
PC5 (ADC5/SCL)
PC4 (ADC4/SDA)
PC3 (ADC3)
PC2 (ADC2)
PC1 (ADC1)
Analog Ground Plane
PC0 (ADC0)
ADC7
ADC6
AREF
GND
100nF 10mH
AVCC
PB5
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5.21.5.3 ADC Accuracy Definitions
An n-bit single-ended ADC converts a voltage linearly between GND and VREF in 2n steps (LSBs). The lowest code is read
as 0, and the highest code is read as 2n-1.
Several parameters describe the deviation from the ideal behavior:
●Offset: The deviation of the first transition (0x000 to 0x001) compared to the ideal transition (at 0.5LSB). Ideal value: 0
LSB.
Figure 5-109. Offset Error
●Gain error: After adjusting for offset, the gain error is found as the deviation of the last transition (0x3FE to 0x3FF)
compared to the ideal transition (at 1.5LSB below maximum). Ideal value: 0LSB
Figure 5-110. Gain Error
Offset
Error
Output Code
Ideal ADC
Actual ADC
V
REF
Input Voltage
Output Code
Ideal ADC
Actual ADC
V
REF
Input Voltage
Gain
Error
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●Integral non-linearity (INL): After adjusting for offset and gain error, the INL is the maximum deviation of an actual
transition compared to an ideal transition for any code. Ideal value: 0LSB.
Figure 5-111. Integral Non-linearity (INL)
●Differential non-linearity (DNL): The maximum deviation of the actual code width (the interval between two adjacent
transitions) from the ideal code width (1LSB). Ideal value: 0LSB.
Figure 5-112. Differential Non-linearity (DNL)
●Quantization error: Due to the quantization of the input voltage into a finite number of codes, a range of input voltages
(1LSB wide) will code to the same value. Always ±0.5LSB.
●Absolute accuracy: The maximum deviation of an actual (unadjusted) transition compared to an ideal transition for
any code. This is the compound effect of offset, gain error, differential error, non-linearity, and quantization error. Ideal
value: ±0.5LSB.
Output Code
Ideal ADC
INL
Actual ADC
V
REF
Input Voltage
Output Code
0x3FF
0x000
0
1 LSB
DNL
VREF Input Voltage
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5.21.6 ADC Conversion Result
After the conversion is complete (ADIF is high), the conversion result can be found in the ADC result registers (ADCL,
ADCH).
For single ended conversion, the result is
where VIN is the voltage on the selected input pin and VREF the selected voltage reference (see Table 5-99 and Table 5-100
on page 236). 0x000 represents analog ground, and 0x3FF represents the selected reference voltage minus one LSB.
5.21.6.1 ADC Multiplexer Selection Register – ADMUX
• Bit 7:6 – REFS1:0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in Table 5-99. If these bits are changed during a conversion,
the change will not go in effect until this conversion is complete (ADIF in ADCSRA is set). The internal voltage reference
options may not be used if an external reference voltage is being applied to the AREF pin.
• Bit 5 – ADLAR: ADC Left Adjust Result
The ADLAR bit affects the presentation of the ADC conversion result in the ADC data register. Write one to ADLAR to left
adjust the result. Otherwise, the result is right adjusted. Changing the ADLAR bit will affect the ADC data register
immediately, regardless of any ongoing conversions. For a complete description of this bit (see Section 5.21.6.3 “The ADC
Data Register – ADCL and ADCH” on page 237).
• Bit 4 – Res: Reserved Bit
This bit is an unused bit in the Atmel® ATA6612C/ATA6613C, and will always read as zero.
• Bits 3:0 – MUX3:0: Analog Channel Selection Bits
The value of these bits selects which analog inputs are connected to the ADC. See Table 5-100 on page 236 for details. If
these bits are changed during a conversion, the change will not go in effect until this conversion is complete (ADIF in
ADCSRA is set).
ADC VIN 1024×
VREF
---------------------------
=
Bit 76543210
REFS1 REFS0 ADLAR – MUX3 MUX2 MUX1 MUX0 ADMUX
Read/Write R/W R/W R/W R R/W R/W R/W R/W
Initial Value00000000
Table 5-99. Voltage Reference Selections for ADC
REFS1 REFS0 Voltage Reference Selection
0 0 AREF, internal Vref turned off
0 1 AVCC with external capacitor at AREF pin
1 0 Reserved
1 1 Internal 1.1V voltage reference with external capacitor at AREF pin
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5.21.6.2 ADC Control and Status Register A – ADCSRA
• Bit 7 – ADEN: ADC Enable
Writing this bit to one enables the ADC. By writing it to zero, the ADC is turned off. Turning the ADC off while a conversion is
in progress, will terminate this conversion.
• Bit 6 – ADSC: ADC Start Conversion
In single conversion mode, write this bit to one to start each conversion. In free running mode, write this bit to one to start the
first conversion. The first conversion after ADSC has been written after the ADC has been enabled, or if ADSC is written at
the same time as the ADC is enabled, will take 25 ADC clock cycles instead of the normal 13. This first conversion performs
initialization of the ADC.
ADSC will read as one as long as a conversion is in progress. When the conversion is complete, it returns to zero. Writing
zero to this bit has no effect.
• Bit 5 – ADATE: ADC Auto Trigger Enable
When this bit is written to one, auto triggering of the ADC is enabled. The ADC will start a conversion on a positive edge of
the selected trigger signal. The trigger source is selected by setting the ADC trigger select bits, ADTS in ADCSRB.
• Bit 4 – ADIF: ADC Interrupt Flag
This bit is set when an ADC conversion completes and the data registers are updated. The ADC conversion complete
interrupt is executed if the ADIE bit and the I-bit in SREG are set. ADIF is cleared by hardware when executing the
corresponding interrupt handling vector. Alternatively, ADIF is cleared by writing a logical one to the flag. Beware that if
doing a read-modify-write on ADCSRA, a pending interrupt can be disabled. This also applies if the SBI and CBI instructions
are used.
Table 5-100. Input Channel Selections
MUX3..0 Single Ended Input
0000 ADC0
0001 ADC1
0010 ADC2
0011 ADC3
0100 ADC4
0101 ADC5
0110 ADC6
0111 ADC7
1000 (reserved)
1001 (reserved)
1010 (reserved)
1011 (reserved)
1100 (reserved)
1101 (reserved)
1110 1.1V (VBG)
1111 0V (GND)
Bit 76543210
ADEN ADSC ADATE ADIF ADIE ADPS2 ADPS1 ADPS0 ADCSRA
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
237
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• Bit 3 – ADIE: ADC Interrupt Enable
When this bit is written to one and the I-bit in SREG is set, the ADC Conversion Complete Interrupt is activated.
• Bits 2:0 – ADPS2:0: ADC Prescaler Select Bits
These bits determine the division factor between the system clock frequency and the input clock to the ADC.
5.21.6.3 The ADC Data Register – ADCL and ADCH
ADLAR = 0
ADLAR = 1
When an ADC conversion is complete, the result is found in these two registers.
When ADCL is read, the ADC data register is not updated until ADCH is read. Consequently, if the result is left adjusted and
no more than 8-bit precision is required, it is sufficient to read ADCH. Otherwise, ADCL must be read first, then ADCH.
The ADLAR bit in ADMUX, and the MUXn bits in ADMUX affect the way the result is read from the registers. If ADLAR is set,
the result is left adjusted. If ADLAR is cleared (default), the result is right adjusted.
• ADC9:0: ADC Conversion Result
These bits represent the result from the conversion, as detailed in Section 5.21.6 “ADC Conversion Result” on page 235.
Table 5-101. ADC Prescaler Selections
ADPS2 ADPS1 ADPS0 Division Factor
0 0 0 2
0 0 1 2
0 1 0 4
0 1 1 8
1 0 0 16
1 0 1 32
1 1 0 64
1 1 1 128
Bit 151413121110 9 8
––––––ADC9ADC8 ADCH
ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADC1 ADC0 ADCL
76543210
Read/Write RRRRRRRR
RRRRRRRR
Initial Value00000000
00000000
Bit 151413121110 9 8
ADC9 ADC8 ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADCH
ADC1ADC0––––––ADCL
76543210
Read/Write RRRRRRRR
RRRRRRRR
Initial Value00000000
00000000
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5.21.6.4 ADC Control and Status Register B – ADCSRB
• Bit 7, 5:3 – Res: Reserved Bits
These bits are reserved for future use. To ensure compatibility with future devices, these bits must be written to zero when
ADCSRB is written.
• Bit 2:0 – ADTS2:0: ADC Auto Trigger Source
If ADATE in ADCSRA is written to one, the value of these bits selects which source will trigger an ADC conversion. If ADATE
is cleared, the ADTS2:0 settings will have no effect. A conversion will be triggered by the rising edge of the selected interrupt
flag. Note that switching from a trigger source that is cleared to a trigger source that is set, will generate a positive edge on
the trigger signal. If ADEN in ADCSRA is set, this will start a conversion. Switching to free running mode (ADTS[2:0]=0) will
not cause a trigger event, even if the ADC interrupt flag is set.
5.21.6.5 Digital Input Disable Register 0 – DIDR0
• Bits 7:6 – Res: Reserved Bits
These bits are reserved for future use. To ensure compatibility with future devices, these bits must be written to zero when
DIDR0 is written.
• Bit 5..0 – ADC5D..ADC0D: ADC5..0 Digital Input Disable
When this bit is written logic one, the digital input buffer on the corresponding ADC pin is disabled. The corresponding PIN
register bit will always read as zero when this bit is set. When an analog signal is applied to the ADC5..0 pin and the digital
input from this pin is not needed, this bit should be written logic one to reduce power consumption in the digital input buffer.
Note that ADC pins ADC7 and ADC6 do not have digital input buffers, and therefore do not require digital input disable bits.
Bit 76543210
– ACME – – – ADTS2 ADTS1 ADTS0 ADCSRB
Read/Write R R/W R R R R/W R/W R/W
Initial Value00000000
Table 5-102. ADC Auto Trigger Source Selections
ADTS2 ADTS1 ADTS0 Trigger Source
000Free running mode
001Analog comparator
010External interrupt request 0
011Timer/Counter0 compare match A
100Timer/Counter0 overflow
101Timer/Counter1 compare match B
110Timer/Counter1 overflow
111Timer/Counter1 capture event
Bit 76543210
––ADC5D ADC4D ADC3D ADC2D ADC1D ADC0D DIDR0
Read/Write R R R/W R/W R/W R/W R/W R/W
Initial Value00000000
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5.22 debugWIRE On-chip Debug System
5.22.1 Features
●Complete program flow control
●Emulates all on-chip functions, both digital and analog, except RESET pin
●Real-time operation
●Symbolic debugging support (both at C and assembler source level, or for other HLLs)
●Unlimited number of program break points (using software break points)
●Non-intrusive operation
●Electrical characteristics identical to real device
●Automatic configuration system
●High-speed operation
●Programming of non-volatile memories
5.22.2 Overview
The debugWIRE on-chip debug system uses a one-wire, bi-directional interface to control the program flow, execute AVR®
instructions in the CPU and to program the different non-volatile memories.
5.22.3 Physical Interface
When the debugWIRE enable (DWEN) fuse is programmed and lock bits are unprogrammed, the debugWIRE system within
the target device is activated. The RESET port pin is configured as a wire-AND (open-drain) bi-directional I/O pin with pull-up
enabled and becomes the communication gateway between target and emulator.
Figure 5-113. The debugWIRE Setup
Figure 5-113 shows the schematic of a target MCU, with debugWIRE enabled, and the emulator connector. The system
clock is not affected by debugWIRE and will always be the clock source selected by the CKSEL fuses.
When designing a system where debugWIRE will be used, the following observations must be made for correct operation:
●Pull-up resistors on the dW/(RESET) line must not be smaller than 10kΩ. The pull-up resistor is not required for
debugWIRE functionality.
●Connecting the RESET pin directly to VCC will not work.
●Capacitors connected to the RESET pin must be disconnected when using debugWire.
●All external reset sources must be disconnected.
GND
2.7 - 5.5V
dW
VCC
dW (RESET)
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5.22.4 Software Break Points
debugWIRE supports program memory break points by the AVR® break instruction. Setting a break point in AVR Studio® will
insert a BREAK instruction in the program memory. The instruction replaced by the BREAK instruction will be stored. When
program execution is continued, the stored instruction will be executed before continuing from the program memory. A break
can be inserted manually by putting the BREAK instruction in the program.
The flash must be re-programmed each time a break point is changed. This is automatically handled by AVR studio through
the debugWIRE interface. The use of break points will therefore reduce the flash data retention. Devices used for debugging
purposes should not be shipped to end customers.
5.22.5 Limitations of debugWIRE
The debugWIRE communication pin (dW) is physically located on the same pin as external reset (RESET). An external reset
source is therefore not supported when the debugWIRE is enabled.
The debugWIRE system accurately emulates all I/O functions when running at full speed, i.e., when the program in the CPU
is running. When the CPU is stopped, care must be taken while accessing some of the I/O registers via the debugger (AVR
Studio).
A programmed DWEN fuse enables some parts of the clock system to be running in all sleep modes. This will increase the
power consumption while in sleep. Thus, the DWEN fuse should be disabled when debugWire is not used.
5.22.6 debugWIRE Related Register in I/O Memory
The following section describes the registers used with the debugWire.
5.22.6.1 debugWire Data Register – DWDR
The DWDR register provides a communication channel from the running program in the MCU to the debugger. This register
is only accessible by the debugWIRE and can therefore not be used as a general purpose register in the normal operations.
5.23 Boot Loader Support – Read-While-Write Self-Programming, Atmel ATA6612C and ATA6613C
In Atmel® ATA6612C and ATA6613C, the boot loader support provides a real read-while-write self-programming mechanism
for downloading and uploading program code by the MCU itself. This feature allows flexible application software updates
controlled by the MCU using a flash-resident boot loader program. The boot loader program can use any available data
interface and associated protocol to read code and write (program) that code into the flash memory, or read the code from
the program memory. The program code within the boot loader section has the capability to write into the entire flash,
including the boot loader memory. The boot loader can thus even modify itself, and it can also erase itself from the code if
the feature is not needed anymore. The size of the boot loader memory is configurable with fuses and the boot loader has
two separate sets of boot lock bits which can be set independently. This gives the user a unique flexibility to select different
levels of protection.
5.23.1 Boot Loader Features
●Read-while-write self-programming
●Flexible boot memory size
●High security (separate boot lock bits for a flexible protection)
●Separate fuse to select reset vector
●Optimized page(1) size
●Code efficient algorithm
●Efficient read-modify-write support
Note: 1. A page is a section in the flash consisting of several bytes (see Table 5-124 on page 258) used during
programming. The page organization does not affect normal operation.
Bit 76543210
DWDR[7:0] DWDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
241
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5.23.2 Application and Boot Loader Flash Sections
The flash memory is organized in two main sections, the application section and the boot loader section (see Figure 5-115
on page 242). The size of the different sections is configured by the BOOTSZ fuses as shown in Table 5-108 on page 251
and Figure 5-115 on page 242. These two sections can have different level of protection since they have different sets of lock
bits.
5.23.2.1 Application Section
The Application section is the section of the flash that is used for storing the application code. The protection level for the
application section can be selected by the application boot lock bits (boot lock bits 0), see Table 5-104 on page 243. The
application section can never store any boot loader code since the SPM instruction is disabled when executed from the
application section.
5.23.2.2 BLS – Boot Loader Section
While the application section is used for storing the application code, the The boot loader software must be located in the
BLS since the SPM instruction can initiate a programming when executing from the BLS only. The SPM instruction can
access the entire flash, including the BLS itself. The protection level for the boot loader section can be selected by the boot
loader lock bits (boot lock bits 1), see Table 5-105 on page 243.
5.23.3 Read-While-Write and No Read-While-Write Flash Sections
Whether the CPU supports read-while-write or if the CPU is halted during a boot loader software update is dependent on
which address that is being programmed. In addition to the two sections that are configurable by the BOOTSZ fuses as
described above, the flash is also divided into two fixed sections, the read-while-write (RWW) section and the No read-while-
write (NRWW) section. The limit between the RWW- and NRWW sections is given in Table 5-109 on page 251 and Figure 5-
115 on page 242. The main difference between the two sections is:
●When erasing or writing a page located inside the RWW section, the NRWW section can be read during the
operation.
●When erasing or writing a page located inside the NRWW section, the CPU is halted during the entire operation.
Note that the user software can never read any code that is located inside the RWW section during a boot loader software
operation. The syntax “read-while-write section” refers to which section that is being programmed (erased or written), not
which section that actually is being read during a boot loader software update.
5.23.3.1 RWW – Read-While-Write Section
If a boot loader software update is programming a page inside the RWW section, it is possible to read code from the flash,
but only code that is located in the NRWW section. During an on-going programming, the software must ensure that the
RWW section never is being read. If the user software is trying to read code that is located inside the RWW section (i.e., by
a call/jmp/lpm or an interrupt) during programming, the software might end up in an unknown state. To avoid this, the
interrupts should either be disabled or moved to the boot loader section. The boot loader section is always located in the
NRWW section. The RWW section busy bit (RWWSB) in the store program memory control and status register (SPMCSR)
will be read as logical one as long as the RWW section is blocked for reading. After a programming is completed, the
RWWSB must be cleared by software before reading code located in the RWW section. See Section 5.23.5.1 “Store
Program Memory Control and Status Register – SPMCSR” on page 244 for details on how to clear RWWSB.
5.23.3.2 NRWW – No Read-While-Write Section
The code located in the NRWW section can be read when the boot loader software is updating a page in the RWW section.
When the boot loader code updates the NRWW section, the CPU is halted during the entire page erase or page write
operation.
Table 5-103. Read-While-Write Features
Which Section does the Z-pointer Address
During the Programming?
Which Section Can be Read
During Programming?
Is the CPU
Halted?
Read-While-Write
Supported?
RWW section NRWW section No Ye s
NRWW section None Yes No
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Figure 5-114. Read-While-Write versus No Read-While-Write
Figure 5-115. Memory Sections
Note: 1. The parameters in the figure above are given in Table 5-108 on page 251.
Z-Pointer
Addresses RWW
Section
Code located in
NRWW Section
can be Read During
the Operation
Z-Pointer
Addresses NRWW
Section
CPU is Halted During
the Operation
Read While Write
(RWW) Section
No Read-While-Write
(RWW) Section
Program Memory
BOOTSZ = ’11’
0x0000
Flashend
Read-While-Write Section
No Read-While-
Write Section
End RWW
Start NRWW
End Application
Start Boot Loader
Program Memory
BOOTSZ = ’10’
0x0000
Flashend
Read-While-Write Section
No Read-While-
Write Section
End RWW
Start NRWW
End Application
Start Boot Loader
Program Memory
BOOTSZ = ’01’
0x0000
Flashend
Read-While-Write Section
No Read-While-
Write Section
End RWW
Start NRWW
End Application
Start Boot Loader
Program Memory
BOOTSZ = ’00’
0x0000
Flashend
Read-While-Write Section
No Read-While-
Write Section
End RWW, End Application
Start NRWW, Start Boot Loader
Application Flash Section
Application Flash Section
Boot Loader Flash Section Boot Loader Flash Section
Application Flash Section
Application Flash Section
Boot Loader Flash Section
Application Flash Section
Application Flash Section
Boot Loader Flash Section
Application Flash Section
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5.23.4 Boot Loader Lock Bits
If no boot loader capability is needed, the entire flash is available for application code. The boot loader has two separate sets
of boot lock bits which can be set independently. This gives the user a unique flexibility to select different levels of protection.
The user can select:
●To protect the entire flash from a software update by the MCU.
●To protect only the boot loader flash section from a software update by the MCU.
●To protect only the application flash section from a software update by the MCU.
●Allow software update in the entire flash.
See Table 5-104 and Table 5-105 for further details. The boot lock bits can be set in software and in serial or parallel
programming mode, but they can be cleared by a chip erase command only. The general write lock (Lock bit mode 2) does
not control the programming of the flash memory by SPM instruction. Similarly, the general read/write lock (Lock bit mode 1)
does not control reading nor writing by LPM/SPM, if it is attempted.
Table 5-104. Boot Lock Bit0 Protection Modes (Application Section)(1)
BLB0 Mode BLB02 BLB01 Protection
1 1 1 No restrictions for SPM or LPM accessing the application section.
2 1 0 SPM is not allowed to write to the application section.
3 0 0
SPM is not allowed to write to the application section, and LPM executing
from the boot loader section is not allowed to read from the application
section. If interrupt vectors are placed in the boot loader section, interrupts
are disabled while executing from the application section.
4 0 1
LPM executing from the boot loader section is not allowed to read from the
application section. If interrupt vectors are placed in the boot loader section,
interrupts are disabled while executing from the application section.
Note: 1. “1” means unprogrammed, “0” means programmed
Table 5-105. Boot Lock Bit1 Protection Modes (Boot Loader Section)(1)
BLB1 Mode BLB12 BLB11 Protection
1 1 1 No restrictions for SPM or LPM accessing the boot loader section.
2 1 0 SPM is not allowed to write to the boot loader section.
3 0 0
SPM is not allowed to write to the boot loader section, and LPM executing
from the application section is not allowed to read from the boot loader
section. If interrupt vectors are placed in the application section, interrupts
are disabled while executing from the boot loader section.
4 0 1
LPM executing from the application section is not allowed to read from the
boot loader section. If interrupt vectors are placed in the application section,
interrupts are disabled while executing from the boot loader section.
Note: 1. “1” means unprogrammed, “0” means programmed
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5.23.5 Entering the Boot Loader Program
Entering the boot loader takes place by a jump or call from the application program. This may be initiated by a trigger such
as a command received via USART, or SPI interface. Alternatively, the boot reset fuse can be programmed so that the reset
vector is pointing to the boot flash start address after a reset. In this case, the boot loader is started after a reset. After the
application code is loaded, the program can start executing the application code. Note that the fuses cannot be changed by
the MCU itself. This means that once the boot reset fuse is programmed, the reset vector will always point to the boot loader
reset and the fuse can only be changed through the serial or parallel programming interface.
5.23.5.1 Store Program Memory Control and Status Register – SPMCSR
The store program memory control and status register contains the control bits needed to control the boot loader operations.
• Bit 7 – SPMIE: SPM Interrupt Enable
When the SPMIE bit is written to one, and the I-bit in the status register is set (one), the SPM ready interrupt will be enabled.
The SPM ready interrupt will be executed as long as the SELFPRGEN bit in the SPMCSR register is cleared.
• Bit 6 – RWWSB: Read-While-Write Section Busy
When a self-programming (page erase or page write) operation to the RWW section is initiated, the RWWSB will be set
(one) by hardware. When the RWWSB bit is set, the RWW section cannot be accessed. The RWWSB bit will be cleared if
the RWWSRE bit is written to one after a self-programming operation is completed. Alternatively the RWWSB bit will
automatically be cleared if a page load operation is initiated.
• Bit 5 – Res: Reserved Bit
This bit is a reserved bit in the Atmel® ATA6612C/ATA6613C and always read as zero.
• Bit 4 – RWWSRE: Read-While-Write Section Read Enable
When programming (page erase or page write) to the RWW section, the RWW section is blocked for reading (the RWWSB
will be set by hardware). To re-enable the RWW section, the user software must wait until the programming is completed
(SELFPRGEN will be cleared). Then, if the RWWSRE bit is written to one at the same time as SELFPRGEN, the next SPM
instruction within four clock cycles re-enables the RWW section. The RWW section cannot be re-enabled while the flash is
busy with a page erase or a page write (SELFPRGEN is set). If the RWWSRE bit is written while the flash is being loaded,
the flash load operation will abort and the data loaded will be lost.
• Bit 3 – BLBSET: Boot Lock Bit Set
If this bit is written to one at the same time as SELFPRGEN, the next SPM instruction within four clock cycles sets boot lock
bits and memory lock bits, according to the data in R0. The data in R1 and the address in the Z-pointer are ignored. The
BLBSET bit will automatically be cleared upon completion of the lock bit set, or if no SPM instruction is executed within four
clock cycles.
An LPM instruction within three cycles after BLBSET and SELFPRGEN are set in the SPMCSR register, will read either the
lock bits or the fuse bits (depending on Z0 in the Z-pointer) into the destination register. See Section 5.23.7.9 “Reading the
Fuse and Lock Bits from Software” on page 248 for details.
Table 5-106. Boot Reset Fuse(1)
BOOTRST Reset Address
1Reset vector = application reset (address 0x0000)
0Reset vector = boot loader reset (see Table 5-108 on page 251)
Note: 1. “1” means unprogrammed, “0” means programmed
Bit 7 6 5 4 3 2 1 0
SPMIE RWWSB – RWWSRE BLBSET PGWRT PGERS SELFPRGEN SPMCSR
Read/Write R/W R R R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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• Bit 2 – PGWRT: Page Write
If this bit is written to one at the same time as SELFPRGEN, the next SPM instruction within four clock cycles executes page
write, with the data stored in the temporary buffer. The page address is taken from the high part of the Z-pointer. The data in
R1 and R0 are ignored. The PGWRT bit will auto-clear upon completion of a page write, or if no SPM instruction is executed
within four clock cycles. The CPU is halted during the entire page write operation if the NRWW section is addressed.
• Bit 1 – PGERS: Page Erase
If this bit is written to one at the same time as SELFPRGEN, the next SPM instruction within four clock cycles executes page
erase. The page address is taken from the high part of the Z-pointer. The data in R1 and R0 are ignored. The PGERS bit will
auto-clear upon completion of a page erase, or if no SPM instruction is executed within four clock cycles. The CPU is halted
during the entire page write operation if the NRWW section is addressed.
• Bit 0 – SELFPRGEN: Self Programming Enable
This bit enables the SPM instruction for the next four clock cycles. If written to one together with either RWWSRE, BLBSET,
PGWRT or PGERS, the following SPM instruction will have a special meaning, see description above. If only SELFPRGEN
is written, the following SPM instruction will store the value in R1:R0 in the temporary page buffer addressed by the
Z-pointer. The LSB of the Z-pointer is ignored. The SELFPRGEN bit will auto-clear upon completion of an SPM instruction,
or if no SPM instruction is executed within four clock cycles. During page erase and page write, the SELFPRGEN bit remains
high until the operation is completed.
Writing any other combination than “10001”, “01001”, “00101”, “00011” or “00001” in the lower five bits will have no effect.
5.23.6 Addressing the Flash During Self-Programming
The Z-pointer is used to address the SPM commands.
Since the flash is organized in pages (see Table 5-124 on page 258), the program counter can be treated as having two
different sections. One section, consisting of the least significant bits, is addressing the words within a page, while the most
significant bits are addressing the pages. This is1 shown in Figure 5-116 on page 246. Note that the page erase and page
write operations are addressed independently. Therefore it is of major importance that the boot loader software addresses
the same page in both the page erase and page write operation. Once a programming operation is initiated, the address is
latched and the Z-pointer can be used for other operations.
The only SPM operation that does not use the Z-pointer is setting the boot loader lock bits. The content of the Z-pointer is
ignored and will have no effect on the operation. The LPM instruction does also use the Z-pointer to store the address. Since
this instruction addresses the flash byte-by-byte, also the LSB (bit Z0) of the Z-pointer is used.
Bit 151413121110 9 8
ZH (R31) Z15 Z14 Z13 Z12 Z11 Z10 Z9 Z8
ZL (R30) Z7 Z6 Z5 Z4 Z3 Z2 Z1 Z0
76543210
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Figure 5-116. Addressing the Flash During SPM(1)
Note: 1. The different variables used in Figure 5-116 are listed in Table 5-110 on page 251.
5.23.7 Self-Programming the Flash
The program memory is updated in a page by page fashion. Before programming a page with the data stored in the
temporary page buffer, the page must be erased. The temporary page buffer is filled one word at a time using SPM and the
buffer can be filled either before the page erase command or between a page erase and a page write operation:
Alternative 1, fill the buffer before a page erase
●Fill temporary page buffer
●Perform a page erase
●Perform a page write
Alternative 2, fill the buffer after page erase
●Perform a page erase
●Fill temporary page buffer
●Perform a page write
If only a part of the page needs to be changed, the rest of the page must be stored (for example in the temporary page
buffer) before the erase, and then be rewritten. When using alternative 1, the boot loader provides an effective read-modify-
write feature which allows the user software to first read the page, do the necessary changes, and then write back the
modified data. If alternative 2 is used, it is not possible to read the old data while loading since the page is already erased.
The temporary page buffer can be accessed in a random sequence. It is essential that the page address used in both the
page erase and page write operation is addressing the same page. See Section 5.23.7.12 “Simple Assembly Code Example
for a Boot Loader” on page 249 for an assembly code example.
5.23.7.1 Performing Page Erase by SPM
To execute page erase, set up the address in the Z-pointer, write “X0000011” to SPMCSR and execute SPM within four
clock cycles after writing SPMCSR. The data in R1 and R0 is ignored. The page address must be written to PCPAGE in the
Z-register. Other bits in the Z-pointer will be ignored during this operation.
●Page erase to the RWW section: The NRWW section can be read during the page erase.
●Page erase to the NRWW section: The CPU is halted during the operation.
BIT
PAGEMSBPCMSB
ZPAGEMSBZPCMSB 0115
Z-REGISTER
PROGRAM
COUNTER
WORD ADDRESS
WITHIN A PAGE
PAGE ADDRESS
WITHIN THE FLASH
0
PCWORDPCPAGE
Instruction Word
Page
02
01
00
PAGEEND
PCWORD[PAGEMSB:0]
Page
Program Memory
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5.23.7.2 Filling the Temporary Buffer (Page Loading)
To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write “00000001” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR. The content of PCWORD in the Z-register is used to address
the data in the temporary buffer. The temporary buffer will auto-erase after a page write operation or by writing the
RWWSRE bit in SPMCSR. It is also erased after a system reset. Note that it is not possible to write more than one time to
each address without erasing the temporary buffer.
If the EEPROM is written in the middle of an SPM page load operation, all data loaded will be lost.
5.23.7.3 Performing a Page Write
To execute page write, set up the address in the Z-pointer, write “X0000101” to SPMCSR and execute SPM within four clock
cycles after writing SPMCSR. The data in R1 and R0 is ignored. The page address must be written to PCPAGE. Other bits
in the Z-pointer must be written to zero during this operation.
●Page write to the RWW section: The NRWW section can be read during the page write.
●Page write to the NRWW section: The CPU is halted during the operation.
5.23.7.4 Using the SPM Interrupt
If the SPM interrupt is enabled, the SPM interrupt will generate a constant interrupt when the SELFPRGEN bit in SPMCSR is
cleared. This means that the interrupt can be used instead of polling the SPMCSR register in software. When using the SPM
interrupt, the interrupt vectors should be moved to the BLS section to avoid that an interrupt is accessing the RWW section
when it is blocked for reading. How to move the interrupts is described in Section 5.8.9 “Watchdog Timer” on page 66.
5.23.7.5 Consideration While Updating BLS
Special care must be taken if the user allows the boot loader section to be updated by leaving boot lock bit11
unprogrammed. An accidental write to the boot loader itself can corrupt the entire boot loader, and further software updates
might be impossible. If it is not necessary to change the boot loader software itself, it is recommended to program the boot
lock bit11 to protect the boot loader software from any internal software changes.
5.23.7.6 Prevent Reading the RWW Section During Self-Programming
During self-programming (either page erase or page write), the RWW section is always blocked for reading. The user
software itself must prevent that this section is addressed during the self programming operation. The RWWSB in the
SPMCSR will be set as long as the RWW section is busy. During self-programming the interrupt vector table should be
moved to the BLS as described in Section 5.8.9 “Watchdog Timer” on page 66, or the interrupts must be disabled. Before
addressing the RWW section after the programming is completed, the user software must clear the RWWSB by writing the
RWWSRE. See Section 5.23.7.12 “Simple Assembly Code Example for a Boot Loader” on page 249 for an example.
5.23.7.7 Setting the Boot Loader Lock Bits by SPM
To set the boot loader lock bits, write the desired data to R0, write “X0001001” to SPMCSR and execute SPM within four
clock cycles after writing SPMCSR. The only accessible lock bits are the boot lock bits that may prevent the application and
boot loader section from any software update by the MCU.
See Table 5-104 on page 243 and Table 5-105 on page 243 for how the different settings of the boot loader bits affect the
flash access.
If bits 5..2 in R0 are cleared (zero), the corresponding boot lock bit will be programmed if an SPM instruction is executed
within four cycles after BLBSET and SELFPRGEN are set in SPMCSR. The Z-pointer is don’t care during this operation, but
for future compatibility it is recommended to load the Z-pointer with 0x0001 (same as used for reading the lOck bits). For
future compatibility it is also recommended to set bits 7, 6, 1, and 0 in R0 to “1” when writing the lock bits. When
programming the lock bits the entire flash can be read during the operation.
5.23.7.8 EEPROM Write Prevents Writing to SPMCSR
Note that an EEPROM write operation will block all software programming to flash. Reading the fuses and lock bits from
software will also be prevented during the EEPROM write operation. It is recommended that the user checks the status bit
(EEPE) in the EECR register and verifies that the bit is cleared before writing to the SPMCSR register.
Bit 76543210
R0 1 1 BLB12 BLB11 BLB02 BLB01 1 1
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5.23.7.9 Reading the Fuse and Lock Bits from Software
It is possible to read both the fuse and lock bits from software. To read the lock bits, load the Z-pointer with 0x0001 and set
the BLBSET and SELFPRGEN bits in SPMCSR. When an LPM instruction is executed within three CPU cycles after the
BLBSET and SELFPRGEN bits are set in SPMCSR, the value of the lock bits will be loaded in the destination register. The
BLBSET and SELFPRGEN bits will auto-clear upon completion of reading the lock bits or if no LPM instruction is executed
within three CPU cycles or no SPM instruction is executed within four CPU cycles. When BLBSET and SELFPRGEN are
cleared, LPM will work as described in the Instruction set Manual.
The algorithm for reading the fuse low byte is similar to the one described above for reading the lock bits. To read the fuse
low byte, load the Z-pointer with 0x0000 and set the BLBSET and SELFPRGEN bits in SPMCSR. When an LPM instruction
is executed within three cycles after the BLBSET and SELFPRGEN bits are set in the SPMCSR, the value of the fuse low
byte (FLB) will be loaded in the destination register as shown below. Refer to Table 5-117 on page 254 for a detailed
description and mapping of the fuse low byte.
Similarly, when reading the fuse high byte, load 0x0003 in the Z-pointer. When an LPM instruction is executed within three
cycles after the BLBSET and SELFPRGEN bits are set in the SPMCSR, the value of the fuse high byte (FHB) will be loaded
in the destination register as shown below. Refer to Table 5-118 on page 255 for detailed description and mapping of the
fuse high byte.
When reading the extended fuse byte, load 0x0002 in the Z-pointer. When an LPM instruction is executed within three cycles
after the BLBSET and SELFPRGEN bits are set in the SPMCSR, the value of the extended fuse byte (EFB) will be loaded in
the destination register as shown below. Refer to Table 5-117 on page 254 for detailed description and mapping of the
extended fuse byte.
Fuse and lock bits that are programmed, will be read as zero. Fuse and lock bits that are unprogrammed, will be read as
one.
5.23.7.10 Preventing Flash Corruption
During periods of low VCC, the flash program can be corrupted because the supply voltage is too low for the CPU and the
flash to operate properly. These issues are the same as for board level systems using the flash, and the same design
solutions should be applied.
A flash program corruption can be caused by two situations when the voltage is too low. First, a regular write sequence to
the flash requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute instructions incorrectly, if the
supply voltage for executing instructions is too low.
Flash corruption can easily be avoided by following these design recommendations (one is sufficient):
1. If there is no need for a boot loader update in the system, program the boot loader lock bits to prevent any boot
loader software updates.
2. Keep the AVR® RESET active (low) during periods of insufficient power supply voltage. This can be done by
enabling the internal brown-out detector (BOD) if the operating voltage matches the detection level. If not, an
external low VCC reset protection circuit can be used. If a reset occurs while a write operation is in progress, the
write operation will be completed provided that the power supply voltage is sufficient.
3. Keep the AVR core in power-down sleep mode during periods of low VCC. This will prevent the CPU from
attempting to decode and execute instructions, effectively protecting the SPMCSR register and thus the flash from
unintentional writes.
Bit 76543210
Rd – – BLB12 BLB11 BLB02 BLB01 LB2 LB1
Bit 76543210
Rd FLB7 FLB6 FLB5 FLB4 FLB3 FLB2 FLB1 FLB0
Bit 76543210
Rd FHB7 FHB6 FHB5 FHB4 FHB3 FHB2 FHB1 FHB0
Bit 76543210
Rd – – – – EFB3 EFB2 EFB1 EFB0
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5.23.7.11 Programming Time for Flash when Using SPM
The calibrated RC oscillator is used to time flash accesses. Table 5-107 shows the typical programming time for flash
accesses from the CPU.
5.23.7.12 Simple Assembly Code Example for a Boot Loader
;-the routine writes one page of data from RAM to Flash
; the first data location in RAM is pointed to by the Y pointer
; the first data location in Flash is pointed to by the Z-pointer
;-error handling is not included
;-the routine must be placed inside the Boot space
; (at least the Do_spm sub routine). Only code inside NRWW section can
; be read during Self-Programming (Page Erase and Page Write).
;-registers used: r0, r1, temp1 (r16), temp2 (r17), looplo (r24),
; loophi (r25), spmcrval (r20)
; storing and restoring of registers is not included in the routine
; register usage can be optimized at the expense of code size
;-It is assumed that either the interrupt table is moved to the Boot
; loader section or that the interrupts are disabled.
.equ PAGESIZEB = PAGESIZE*2;PAGESIZEB is page size in BYTES, not words
.org SMALLBOOTSTART
Write_page:
; Page Erase
ldi spmcrval, (1<<PGERS) | (1<<SELFPRGEN)
call Do_spm
; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SELFPRGEN)
call Do_spm
; transfer data from RAM to Flash page buffer
ldi looplo, low(PAGESIZEB) ;init loop variable
ldi loophi, high(PAGESIZEB) ;not required for PAGESIZEB<=256
Wrloop:
ld r0, Y+
ld r1, Y+
ldi spmcrval, (1<<SELFPRGEN)
call Do_spm
adiw ZH:ZL, 2
sbiw loophi:looplo, 2 ;use subi for PAGESIZEB<=256
brne Wrloop
; execute Page Write
subi ZL, low(PAGESIZEB) ;restore pointer
sbci ZH, high(PAGESIZEB) ;not required for PAGESIZEB<=256
ldi spmcrval, (1<<PGWRT) | (1<<SELFPRGEN)
call Do_spm
; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SELFPRGEN)
call Do_spm
Table 5-107. SPM Programming Time
Symbol Min Programming Time Max Programming Time
Flash write (page erase, page write, and write lock
bits by SPM) 3.7ms 4.5ms
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; read back and check, optional
ldi looplo, low(PAGESIZEB) ;init loop variable
ldi loophi, high(PAGESIZEB) ;not required for PAGESIZEB<=256
subi YL, low(PAGESIZEB) ;restore pointer
sbci YH, high(PAGESIZEB)
Rdloop:
lpm r0, Z+
ld r1, Y+
cpse r0, r1
jmp Error
sbiw loophi:looplo, 1 ;use subi for PAGESIZEB<=256
brne Rdloop
; return to RWW section
; verify that RWW section is safe to read
Return:
in temp1, SPMCSR
sbrs temp1, RWWSB ; If RWWSB is set, the RWW section is not
ready yet
ret
; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SELFPRGEN)
call Do_spm
rjmp Return
Do_spm:
; check for previous SPM complete
Wait_spm:
in temp1, SPMCSR
sbrc temp1, SELFPRGEN
rjmp Wait_spm
; input: spmcrval determines SPM action
; disable interrupts if enabled, store status
in temp2, SREG
cli
; check that no EEPROM write access is present
Wait_ee:
sbic EECR, EEPE
rjmp Wait_ee
; SPM timed sequence
out SPMCSR, spmcrval
spm
; restore SREG (to enable interrupts if originally enabled)
out SREG, temp2
ret
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5.23.7.13 Atmel ATA6612C Boot Loader Parameters
In Table 5-108 through Table 5-110, the parameters used in the description of the self programming are given.
For details about these two section, see Section 5.23.3.2 “NRWW – No Read-While-Write Section” on page 241 and
Section 5.23.3.1 “RWW – Read-While-Write Section” on page 241.
Table 5-108. Boot Size Configuration, Atmel ATA6612C
BOOTSZ1 BOOTSZ0 Boot Size Pages
Application
Flash Section
Boot Loader
Flash Section
End
Application
Section
Boot Reset
Address (Start
Boot Loader
Section)
1 1 128 words 40x000 - 0xF7F 0xF80 - 0xFFF 0xF7F 0xF80
1 0 256 words 80x000 - 0xEFF 0xF00 - 0xFFF 0xEFF 0xF00
0 1 512 words 16 0x000 - 0xDFF 0xE00 - 0xFFF 0xDFF 0xE00
0 0 1024 words 32 0x000 - 0xBFF 0xC00 - 0xFFF 0xBFF 0xC00
Note: The different BOOTSZ fuse configurations are shown in Figure 5-115 on page 242.
Table 5-109. Read-While-Write Limit, Atmel ATA6612C
Section Pages Address
Read-while-write section (RWW) 96 0x000 - 0xBFF
No read-while-write section (NRWW) 32 0xC00 - 0xFFF
Table 5-110. Explanation of Different Variables used in Figure 5-116 on page 246 and the Mapping to the Z-pointer,
Atmel ATA6612C
Variable
Corresponding
Z-value(1) Description
PCMSB 11 Most significant bit in the program counter. (the program
counter is 12 bits PC[11:0])
PAGEMSB 4Most significant bit which is used to address the words within
one page (32 words in a page requires 5 bits PC [4:0]).
ZPCMSB Z12 Bit in Z-register that is mapped to PCMSB. Because Z0 is not
used, the ZPCMSB equals PCMSB + 1.
ZPAGEMSB Z5 Bit in Z-register that is mapped to PAGEMSB. Because Z0 is
not used, the ZPAGEMSB equals PAGEMSB + 1.
PCPAGE PC[11:5] Z12:Z6 Program counter page address: Page select, for page erase
and page write
PCWORD PC[4:0] Z5:Z1 Program counter word address: Word select, for filling
temporary buffer (must be zero during page write operation)
Note: 1. Z15:Z13: always ignored
Z0: should be zero for all SPM commands, byte select for the LPM instruction.
See Section 5.23.6 “Addressing the Flash During Self-Programming” on page 245 for details about the use of
Z-pointer during Self-Programming.
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5.23.7.14 ATA6613C Boot Loader Parameters
In Table 5-111 through Table 5-113, the parameters used in the description of the self programming are given.
For details about these two section, see Section 5.23.3.2 “NRWW – No Read-While-Write Section” on page 241 and
Section 5.23.3.1 “RWW – Read-While-Write Section” on page 241.
Table 5-111. Boot Size Configuration, ATA6613C
BOOTSZ1 BOOTSZ0 Boot Size Pages
Application
Flash Section
Boot Loader
Flash Section
End
Application
Section
Boot Reset
Address (Start
Boot Loader
Section)
1 1 128 words 20x0000 - 0x1F7F 0x1F80 - 0x1FFF 0x1F7F 0x1F80
1 0 256 words 40x0000 - 0x1EFF 0x1F00 - 0x1FFF 0x1EFF 0x1F00
0 1 512 words 80x0000 - 0x1DFF 0x1E00 - 0x1FFF 0x1DFF 0x1E00
0 0 1024 words 16 0x0000 - 0x1BFF 0x1C00 - 0x1FFF 0x1BFF 0x1C00
Note: The different BOOTSZ fuse configurations are shown in Figure 5-115 on page 242.
Table 5-112. Read-While-Write Limit, ATA6613C
Section Pages Address
Read-while-write section (RWW) 112 0x0000 - 0x1BFF
No read-while-write section (NRWW) 16 0x1C00 - 0x1FFF
Table 5-113. Explanation of Different Variables used in Figure 5-116 on page 246 and the Mapping to the Z-pointer,
ATA6613C
Variable
Corresponding
Z-value(1) Description
PCMSB 12 Most significant bit in the program counter. (The program counter
is 12 bits PC[11:0])
PAGEMSB 5Most significant bit which is used to address the words within one
page (64 words in a page requires 6 bits PC [5:0])
ZPCMSB Z13 Bit in Z-register that is mapped to PCMSB. Because Z0 is not
used, the ZPCMSB equals PCMSB + 1.
ZPAGEMSB Z6 Bit in Z-register that is mapped to PAGEMSB. Because Z0 is not
used, the ZPAGEMSB equals PAGEMSB + 1.
PCPAGE PC[12:6] Z13:Z7 Program counter page address: Page select, for page erase and
page write
PCWORD PC[5:0] Z6:Z1 Program counter word address: Word select, for filling temporary
buffer (must be zero during page write operation)
Note: 1. Z15:Z14: always ignored
Z0: should be zero for all SPM commands, byte select for the LPM instruction.
See Section 5.23.6 “Addressing the Flash During Self-Programming” on page 245 for details about the use of
Z-pointer during self-programming.
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5.24 Memory Programming
5.24.1 Program And Data Memory Lock Bits
The Atmel® ATA6612C/ATA6613C provides six lock bits which can be left unprogrammed (“1”) or can be programmed (“0”)
to obtain the additional features listed in Table 5-115. The lock bits can only be erased to “1” with the chip erase command.
The SPM instruction is enabled for the whole flash if the SELFPRGEN fuse is programmed (“0”), otherwise it is disabled.
Table 5-114. Lock Bit Byte(1)
Lock Bit Byte Bit No Description Default Value
7 – 1 (unprogrammed)
6 – 1 (unprogrammed)
BLB12(2) 5 Boot lock bit 1 (unprogrammed)
BLB11(2) 4 Boot lock bit 1 (unprogrammed)
BLB02(2) 3 Boot lock bit 1 (unprogrammed)
BLB01(2) 2 Boot lock bit 1 (unprogrammed)
LB2 1Lock bit 1 (unprogrammed)
LB1 0Lock bit 1 (unprogrammed)
Notes: 1. “1” means unprogrammed, “0” means programmed
2. Only on Atmel ATA6612C/ATA6613C
Table 5-115. Lock Bit Protection Modes(1)(2)
Memory Lock Bits Protection Type
LB Mode LB2 LB1
1 1 1 No memory lock features enabled.
2 1 0
Further programming of the flash and EEPROM is disabled in parallel and
serial programming mode. The fuse bits are locked in both serial and parallel
programming mode.(1)
3 0 0
Further programming and verification of the flash and EEPROM is disabled in
parallel and serial programming mode. The boot lock bits and fuse bits are
locked in both serial and parallel programming mode.(1)
Notes: 1. Program the fuse bits and boot lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
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5.24.2 Fuse Bits
The Atmel ATA6612C/ATA6613C has three Fuse bytes. Table 5-117 to Table 5-119 on page 255 describe briefly the
functionality of all the fuses and how they are mapped into the Fuse bytes. Note that the fuses are read as logical zero, “0”, if
they are programmed.
Table 5-116. Lock Bit Protection Modes(1)(2). Only Atmel ATA6612C/ATA6613C.
BLB0 Mode BLB02 BLB01
1 1 1 No restrictions for SPM or LPM accessing the application section.
2 1 0 SPM is not allowed to write to the application section.
3 0 0
SPM is not allowed to write to the application section, and LPM executing from
the boot loader section is not allowed to read from the application section. If
interrupt vectors are placed in the boot loader section, interrupts are disabled
while executing from the application section.
4 0 1
LPM executing from the boot loader section is not allowed to read from the
application section. If interrupt vectors are placed in the boot loader section,
interrupts are disabled while executing from the application section.
BLB1 Mode BLB12 BLB11
1 1 1 No restrictions for SPM or LPM accessing the boot loader section.
2 1 0 SPM is not allowed to write to the boot loader section.
3 0 0
SPM is not allowed to write to the boot loader section, and LPM executing from
the application section is not allowed to read from the boot loader section. If
interrupt vectors are placed in the application section, interrupts are disabled
while executing from the boot loader section.
4 0 1
LPM executing from the application section is not allowed to read from the boot
loader section. If interrupt vectors are placed in the application section,
interrupts are disabled while executing from the boot loader section.
Notes: 1. Program the Fuse bits and Boot Lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
Table 5-117. Extended Fuse Byte for Atmel ATA6612C/ATA6613C
Extended Fuse Byte Bit No Description Default Value
– 7 – 1
– 6 – 1
– 5 – 1
– 4 – 1
– 3 – 1
BOOTSZ1 2Select boot size
(see Table 113 for details) 0 (programmed)(1)
BOOTSZ0 1Select boot size
(see Table 113 for details) 0 (programmed)(1)
BOOTRST 0Select reset vector 1 (unprogrammed)
Note: 1. The default value of BOOTSZ1..0 results in maximum boot size. See Table 5-120 on page 257 for details.
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The status of the fuse bits is not affected by chip erase. Note that the fuse bits are locked if lock bit1 (LB1) is programmed.
program the fuse bits before programming the lock bits.
5.24.2.1 Latching of Fuses
The fuse values are latched when the device enters programming mode and changes of the fuse values will have no effect
until the part leaves Programming mode. This does not apply to the EESAVE fuse which will take effect once it is
programmed. The fuses are also latched on power-up in normal mode.
5.24.3 Signature Bytes
All Atmel® microcontrollers have a three-byte signature code which identifies the device. This code can be read in both serial
and parallel mode, also when the device is locked. The three bytes reside in a separate address space.
Table 5-118. Fuse High Byte
High Fuse Byte Bit No Description Default Value
RSTDISBL(1) 7External reset disable 1 (unprogrammed)
DWEN 6 debugWIRE enable 1 (unprogrammed)
SPIEN(2) 5Enable serial program and data
downloading
0 (programmed, SPI programming
enabled)
WDTON(3) 4Watchdog timer always on 1 (unprogrammed)
EESAVE 3EEPROM memory is preserved
through the chip erase
1 (unprogrammed), EEPROM not
reserved
BODLEVEL2(4) 2Brown-out detector trigger level 1 (unprogrammed)
BODLEVEL1(4) 1Brown-out detector trigger level 1 (unprogrammed)
BODLEVEL0(4) 0Brown-out detector trigger level 1 (unprogrammed)
Notes: 1. See Section 5.10.3.3 “Alternate Functions of Port C” on page 87 for description of RSTDISBL fuse.
2. The SPIEN fuse is not accessible in serial programming mode.
3. See Section 5.8.9.1 “Watchdog Timer Control Register - WDTCSR” on page 68 for details.
4. See Table 5-21 on page 63 for BODLEVEL fuse decoding.
Table 5-119. Fuse Low Byte
Low Fuse Byte Bit No Description Default Value
CKDIV8(4) 7Divide clock by 8 0 (programmed)
CKOUT(3) 6Clock output 1 (unprogrammed)
SUT1 5Select start-up time 1 (unprogrammed)(1)
SUT0 4Select start-up time 0 (programmed)(1)
CKSEL3 3Select clock source 0 (programmed)(2)
CKSEL2 2Select clock source 0 (programmed)(2)
CKSEL1 1Select clock source 1 (unprogrammed)(2)
CKSEL0 0Select clock source 0 (programmed)(2)
Notes: 1. The default value of SUT1..0 results in maximum start-up time for the default clock source.
See Table 5-12 on page 52 for details.
2. The default setting of CKSEL3..0 results in internal RC Oscillator at 8 MHz. See Table 5-11 on page 51 for
details.
3. The CKOUT fuse allows the system clock to be output on PORTB0. See Section 5.6.9 “Clock Output Buffer”
on page 54 for details.
4. See Section 5.6.11 “System Clock Prescaler” on page 54 for details.
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5.24.3.1 Atmel ATA6612C Signature Bytes
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x93 (indicates 8KB Flash memory).
3. 0x002: 0x0A (indicates Atmel ATA6612C device when 0x001 is 0x93).
5.24.3.2 ATA6613C Signature Bytes
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x94 (indicates 16KB Flash memory).
3. 0x002: 0x06 (indicates ATA6613C device when 0x001 is 0x94).
5.24.4 Calibration Byte
The Atmel® ATA6612C/ATA6613C has a byte calibration value for the internal RC oscillator. This byte resides in the high
byte of address 0x000 in the signature address space. During reset, this byte is automatically written into the OSCCAL
Register to ensure correct frequency of the calibrated RC Oscillator.
5.24.5 Parallel Programming Parameters, Pin Mapping, and Commands
This section describes how to parallel program and verify flash program memory, EEPROM data memory, memory lock bits,
and fuse bits in the Atmel ATA6612C/ATA6613C. Pulses are assumed to be at least 250ns unless otherwise noted.
5.24.5.1 Signal Names
In this section, some pins of the Atmel ATA6612C/ATA6613C are referenced by signal names describing their functionality
during parallel programming (see Figure 5-117 and Table 5-120 on page 257). Pins not described in the following table are
referenced by pin names.
The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse. The bit coding is shown in
Table 5-122 on page 257.
When pulsing WR or OE, the command loaded determines the action executed. The different commands are shown in Table
5-123 on page 257.
Figure 5-117. Parallel Programming
GND
XTAL1
PC2
PD1
PD2
PD3
PD4
DATA
PD5
PD6
PD7
RESET
VCC
AVCC
PC[1:0]:PB[5:0]
+ 5V
+ 5V
RDY/BSY
OE
WR
BS1
XA0
XA1
PAGEL
+12V
BS2
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Table 5-120. Pin Name Mapping
Signal Name in
Programming Mode Pin Name I/O Function
RDY/BSY PD1 O0: Device is busy programming, 1: Device is ready for new
command
OE PD2 IOutput enable (active low)
WR PD3 IWrite pulse (active low)
BS1 PD4 IByte select 1 (“0” selects Low byte, “1” selects high byte)
XA0 PD5 IXTAL action Bit 0
XA1 PD6 IXTAL action Bit 1
PAGEL PD7 IProgram memory and EEPROM data page load
BS2 PC2 IByte select 2 (“0” selects low byte, “1” selects 2’nd high
byte)
DATA {PC[1:0]: PB[5:0]} I/O Bi-directional data bus (output when OE is low)
Table 5-121. Pin Values Used to Enter Programming Mode
Pin Symbol Value
PAGEL Prog_enable[3] 0
XA1 Prog_enable[2] 0
XA0 Prog_enable[1] 0
BS1 Prog_enable[0] 0
Table 5-122. XA1 and XA0 Coding
XA1 XA0 Action when XTAL1 is Pulsed
0 0 Load flash or EEPROM address (high or low address byte determined by BS1).
0 1 Load data (high or low data byte for flash determined by BS1).
1 0 Load command
1 1 No action, idle
Table 5-123. Command Byte Bit Coding
Command Byte Command Executed
1000 0000 Chip erase
0100 0000 Write fuse bits
0010 0000 Write lock bits
0001 0000 Write flash
0001 0001 Write EEPROM
0000 1000 Read signature bytes and calibration byte
0000 0100 Read fuse and lock bits
0000 0010 Read flash
0000 0011 Read EEPROM
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5.24.6 Serial Programming Pin Mapping
5.24.7 Parallel Programming
5.24.7.1 Enter Programming Mode
The following algorithm puts the device in parallel programming mode:
1. Apply 4.5 - 5.5V between VCC and GND.
2. Set RESET to “0” and toggle XTAL1 at least six times.
3. Set the Prog_enable pins listed in Table 5-121 on page 257 to “0000” and wait at least 100ns.
4. Apply 11.5 - 12.5V to RESET
. Any activity on Prog_enable pins within 100ns after +12V has been applied to
RESET, will cause the device to fail entering programming mode.
5. Wait at least 50µs before sending a new command.
5.24.7.2 Considerations for Efficient Programming
The loaded command and address are retained in the device during programming. For efficient programming, the following
should be considered.
●The command needs only be loaded once when writing or reading multiple memory locations.
●Skip writing the data value 0xFF, that is the contents of the entire EEPROM (unless the EESAVE fuse is programmed)
and flash after a chip erase.
●Address high byte needs only be loaded before programming or reading a new 256 word window in flash or 256 byte
EEPROM. This consideration also applies to signature bytes reading.
Table 5-124. No. of Words in a Page and No. of Pages in the Flash
Device Flash Size Page Size PCWORD No. of Pages PCPAGE PCMSB
ATA6612C 4Kwords
(8Kbytes) 32 words PC[4:0] 128 PC[11:5] 11
ATA6613C 8Kwords
(16Kbytes) 64 words PC[5:0] 128 PC[12:6] 12
Table 5-125. No. of Words in a Page and No. of Pages in the EEPROM
Device EEPROM Size Page Size PCWORD No. of Pages PCPAGE EEAMSB
ATA6612C 512 bytes 4 bytes EEA[1:0] 128 EEA[8:2] 8
ATA6613C 512 bytes 4 bytes EEA[1:0] 128 EEA[8:2] 8
Table 5-126. Pin Mapping Serial Programming
Symbol Pins I/O Description
MOSI PB3 ISerial data in
MISO PB4 OSerial data out
SCK PB5 ISerial clock
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5.24.7.3 Chip Erase
The chip erase will erase the flash and EEPROM(1) memories plus lock bits. The lock bits are not reset until the program
memory has been completely erased. The fuse bits are not changed. A chip erase must be performed before the flash
and/or EEPROM are reprogrammed.
Note: 1. The EEPRPOM memory is preserved during chip erase if the EESAVE fuse is programmed.
Load command “chip erase”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “1000 0000”. This is the command for chip erase.
4. Give XTAL1 a positive pulse. This loads the command.
5. Give WR a negative pulse. This starts the chip erase. RDY/BSY goes low.
6. Wait until RDY/BSY goes high before loading a new command.
5.24.7.4 Programming the Flash
The flash is organized in pages (see Table 5-124 on page 258). When programming the flash, the program data is latched
into a page buffer. This allows one page of program data to be programmed simultaneously. The following procedure
describes how to program the entire flash memory:
A. Load command “write flash”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “0001 0000”. This is the command for write flash.
4. Give XTAL1 a positive pulse. This loads the command.
B. Load address low byte
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “0”. This selects low address.
3. Set DATA = address low byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address low byte.
C. Load data low byte
1. Set XA1, XA0 to “01”. This enables data loading.
2. Set DATA = data low byte (0x00 - 0xFF).
3. Give XTAL1 a positive pulse. This loads the data byte.
D. Load data high byte
1. Set BS1 to “1”. This selects high data byte.
2. Set XA1, XA0 to “01”. This enables data loading.
3. Set DATA = data high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the data byte.
E. Latch data
1. Set BS1 to “1”. This selects high data byte.
2. Give PAGEL a positive pulse. This latches the data bytes (see Figure 5-119 on page 261 for signal waveforms).
F. Repeat B through E until the entire buffer is filled or until all data within the page is loaded.
While the lower bits in the address are mapped to words within the page, the higher bits address the pages within the
FLASH. This is illustrated in Figure 5-118 on page 260. Note that if less than eight bits are required to address words in the
page (pagesize < 256), the most significant bit(s) in the address low byte are used to address the page when performing a
page write.
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G. Load address high byte
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “1”. This selects high address.
3. Set DATA = address high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address high byte.
H. Program page
1. Give WR a negative pulse. This starts programming of the entire page of data. RDY/BSY goes low.
2. Wait until RDY/BSY goes high (see Figure 5-119 on page 261 for signal waveforms).
I. Repeat B through H until the entire Flash is programmed or until all data has been programmed.
J. End page programming
1. 1. Set XA1, XA0 to “10”. This enables command loading.
2. Set DATA to “0000 0000”. This is the command for No operation.
3. Give XTAL1 a positive pulse. This loads the command, and the internal write signals are reset.
Figure 5-118. Addressing the Flash Which is Organized in Pages(1)
Note: 1. PCPAGE and PCWORD are listed in Table 5-124 on page 258.
PAGEMSBPCMSB
PROGRAM
COUNTER
WORD ADDRESS
WITHIN A PAGE
PAGE ADDRESS
WITHIN THE FLASH
PCWORDPCPAGE
02
01
00
PAGEEND
PCWORD [PAGEMSB:0]
Page
Program Memory
Instructions Word
Page
261
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Figure 5-119. Programming the Flash Waveforms(1)
Note: 1. “XX” is do not care. The letters refer to the programming description above.
5.24.7.5 Programming the EEPROM
The EEPROM is organized in pages (see Table 5-125 on page 258). When programming the EEPROM, the program data is
latched into a page buffer. This allows one page of data to be programmed simultaneously. The programming algorithm for
the EEPROM data memory is as follows (refer to Section 5.24.7.4 “Programming the Flash” on page 259 for details on
command, address and data loading):
1. A: Load command “0001 0001”.
2. G: Load address high byte (0x00 - 0xFF).
3. B: Load address low byte (0x00 - 0xFF).
4. C: Load data (0x00 - 0xFF).
5. E: Latch data (give PAGEL a positive pulse).
K: Repeat 3 through 5 until the entire buffer is filled.
L: Program EEPROM page
1. Set BS1 to “0”.
2. Give WR a negative pulse. This starts programming of the EEPROM page. RDY/BSY goes low.
3. Wait until to RDY/BSY goes high before programming the next page (see Figure 5-120 on page 262 for signal
waveforms).
XTAL1
PAGEL
RDY/BSY
OE
RESET +12V
BS2
BS1
XA0
XA1
DATA
ABCDEBCDEGH
0x10 XXXXXX ADDR. HIGHADDR. LOWADDR. LOW DATA HIGHDATA HIGH DATA LOWDATA LOW
WR
F
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Figure 5-120.Programming the EEPROM Waveforms
5.24.7.6 Reading the Flash
The algorithm for reading the flash memory is as follows (refer to Section 5.24.7.4 “Programming the Flash” on page 259 for
details on command and address loading):
1. A: Load command “0000 0010”.
2. G: Load address high byte (0x00 - 0xFF).
3. B: Load address low byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The flash word low byte can now be read at DATA.
5. Set BS1 to “1”. The flash word high byte can now be read at DATA.
6. Set OE to “1”.
5.24.7.7 Reading the EEPROM
The algorithm for reading the EEPROM memory is as follows (refer to Section 5.24.7.4 “Programming the Flash” on page
259 for details on command and address loading):
1. A: Load Command “0000 0011”.
2. G: Load address high byte (0x00 - 0xFF).
3. B: Load address Low Byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The EEPROM Data byte can now be read at DATA.
5. Set OE to “1”.
5.24.7.8 Programming the Fuse Low Bits
The algorithm for programming the fuse low bits is as follows (refer to Section 5.24.7.4 “Programming the Flash” on page
259 for details on command and data loading):
1. A: Load command “0100 0000”.
2. C: Load data low byte. Bit n = “0” programs and bit n = “1” erases the fuse bit.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
XTAL1
PAGEL
RDY/ BSY
OE
RESET +12V
BS1
BS2
XA0
XA1
DATA
WR
ABCEBC
K
EG
ADDR. HIGH ADDR. LOW0x11 DATA XX ADDR. LOW DATA XX
L
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5.24.7.9 Programming the Fuse High Bits
The algorithm for programming the fuse High bits is as follows (refer to Section 5.24.7.4 “Programming the Flash” on page
259 for details on command and data loading):
1. A: Load command “0100 0000”.
2. C: Load data low byte. Bit n = “0” programs and bit n = “1” erases the fuse bit.
3. Set BS1 to “1” and BS2 to “0”. This selects high data byte.
4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. Set BS1 to “0”. This selects low data byte.
5.24.7.10 Programming the Extended Fuse Bits
The algorithm for programming the extended Fuse bits is as follows (refer to Section 5.24.7.4 “Programming the Flash” on
page 259 for details on command and data loading):
1. 1. A: Load command “0100 0000”.
2. 2. C: Load Data low byte. Bit n = “0” programs and bit n = “1” erases the fuse bit.
3. 3. Set BS1 to “0” and BS2 to “1”. This selects extended data byte.
4. 4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. 5. Set BS2 to “0”. This selects low data byte.
Figure 5-121.Programming the FUSES Waveforms
5.24.7.11 Programming the Lock Bits
The algorithm for programming the Lock bits is as follows (refer to “Programming the Flash” on page 259 for details on
Command and Data loading):
1. A: Load Command “0010 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs the Lock bit. If LB mode 3 is programmed (LB1 and LB2 is pro-
grammed), it is not possible to program the Boot Lock bits by any External Programming mode.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
The Lock bits can only be cleared by executing Chip Erase.
XTAL1
RDY/ BSY
OE
RESET +12V
BS1
BS2
PAGEL
XA0
XA1
DATA
WR
AC
0x40 DAT A XX
AC
DATA DATAXX XX
AC
0x400x40
Write Fuse Low Byte Write Fuse High Byte Write Extended FuseByte
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5.24.7.12 Reading the Fuse and Lock Bits
The algorithm for reading the fuse and lock bits is as follows (refer to Section 5.24.7.4 “Programming the Flash” on page 259
for details on command loading):
1. A: Load command “0000 0100”.
2. Set OE to “0”, BS2 to “0” and BS1 to “0”. The status of the fuse low bits can now be read at DATA (“0” means
programmed).
3. Set OE to “0”, BS2 to “1” and BS1 to “1”. The status of the fuse high bits can now be read at DATA (“0” means
programmed).
4. Set OE to “0”, BS2 to “1”, and BS1 to “0”. The status of the extended fuse bits can now be read at DATA (“0”
means programmed).
5. Set OE to “0”, BS2 to “0” and BS1 to “1”. The status of the lock bits can now be read at DATA (“0” means
programmed).
6. Set OE to “1”.
Figure 5-122. Mapping Between BS1, BS2 and the Fuse and Lock Bits During Read
5.24.7.13 Reading the Signature Bytes
The algorithm for reading the signature bytes is as follows (refer to Section 5.24.7.4 “Programming the Flash” on page 259
for details on command and address loading):
1. A: Load command “0000 1000”.
2. B: Load Address low byte (0x00 - 0x02).
3. Set OE to “0”, and BS1 to “0”. The selected signature byte can now be read at DATA.
4. Set OE to “1”.
5.24.7.14 Reading the Calibration Byte
The algorithm for reading the calibration byte is as follows (refer to Section 5.24.7.4 “Programming the Flash” on page 259
for details on command and Address loading):
1. A: Load command “0000 1000”.
2. B: Load address low byte, 0x00.
3. Set OE to “0”, and BS1 to “1”. The calibration byte can now be read at DATA.
4. Set OE to “1”.
Fuse Low Byte
Extended Fuse Byte
BS2
BS1
DAT
A
BS2
Lock Bits
Fuse High Byte 1
0
1
0
1
0
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5.24.7.15 Parallel Programming Characteristics
Figure 5-123. Parallel Programming Timing, Including some General Timing Requirements
Figure 5-124. Parallel Programming Timing, Loading Sequence with Timing Requirements(1)
Note: 1. The timing requirements shown in Figure 5-123 on page 265 (i.e., tDVXH, tXHXL, and tXLDX) also apply to loading
operation.
XTAL1
PAGEL
WR
Data and Control
(DATA, XA0/1, BS1, BS2)
tXHXL
tDVXH
tBVPH
tXLWL
tXLDX
tPHPL
tPLBX
tPLWL
tBVWL tWLBX
tWLWH
tWLRL
tWLRH
RDY/BSY
XTAL1
BS1
PAGEL
DATA
XA0
XA1
tXLXH tPLXH
tXLPH
Load Address
(Low Byte)
Load Data
(Low Byte)
Load Data
(High Byte)
Load Address
(Low Byte)
Load Data
ADDR0 (Low Byte) ADDR1 (Low Byte)DATA (Low Byte) DATA (High Byte)
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Figure 5-125. Parallel Programming Timing, Reading Sequence (within the Same Page) with Timing
Requirements(1)
Note: 1. The timing requirements shown in Figure 5-123 on page 265 (i.e., tDVXH, tXHXL, and tXLDX) also apply to
reading operation.
Table 5-127. Parallel Programming Characteristics, VCC = 5V ±10%
Parameter Symbol Min Typ Max Units
Programming enable voltage VPP 11.5 12.5 V
Programming enable current IPP 250 µA
Data and control valid before XTAL1 high tDVXH 67 ns
XTAL1 low to XTAL1 high tXLXH 200 ns
XTAL1 pulse width high tXHXL 150 ns
Data and control hold after XTAL1 low tXLDX 67 ns
XTAL1 low to WR low tXLWL 0ns
XTAL1 low to PAGEL high tXLPH 0ns
PAGEL low to XTAL1 high tPLXH 150 ns
BS1 valid before PAGEL high tBVPH 67 ns
PAGEL pulse width high tPHPL 150 ns
BS1 hold after PAGEL low tPLBX 67 ns
BS2/1 hold after WR low tWLBX 67 ns
PAGEL low to WR low tPLWL 67 ns
BS1 valid to WR low tBVWL 67 ns
WR pulse width low tWLWH 150 ns
WR low to RDY/BSY low tWLRL 0 1 µs
WR low to RDY/BSY high(1) tWLRH 3.7 4.5 ms
WR low to RDY/BSY high for chip erase(2) tWLRH_CE 7.5 9ms
XTAL1 low to OE low tXLOL 0ns
BS1 valid to DATA valid tBVDV 0250 ns
OE low to DATA valid tOLDV 250 ns
OE high to DATA tri-stated tOHDZ 250 ns
Notes: 1. tWLRH is valid for the write flash, write EEPROM, write fuse bits and write lock bits commands.
2. tWLRH_CE is valid for the chip erase command.
XTAL1
BS1
OE
DATA
XA0
XA1
tBVDV
tXLOL
tOLDV
tOHDZ
Load Address
(Low Byte)
Read Data
(Low Byte)
Read Data
(High Byte)
Load Address
(Low Byte)
ADDR0 (Low Byte) ADDR1 (Low Byte)DATA (Low Byte) DATA (High Byte)
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5.24.8 Serial Downloading
Both the flash and EEPROM memory arrays can be programmed using the serial SPI bus while RESET is pulled to GND.
The serial interface consists of pins SCK, MOSI (input) and MISO (output). After RESET is set low, the programming enable
instruction needs to be executed first before program/erase operations can be executed. NOTE, in Table 5-126 on page 258,
the pin mapping for SPI programming is listed. Not all parts use the SPI pins dedicated for the internal SPI interface.
Figure 5-126. Serial Programming and Verify(1)
Notes: 1. If the device is clocked by the internal oscillator, it is no need to connect a clock source to the XTAL1 pin.
2. VCC – 0.3V < AVCC < VCC + 0.3V, however, AVCC should always be within 1.8V – 5.5V
When programming the EEPROM, an auto-erase cycle is built into the self-timed programming operation (in the serial mode
ONLY) and there is no need to first execute the chip erase instruction. The chip erase operation turns the content of every
memory location in both the program and EEPROM arrays into 0xFF.
Depending on CKSEL fuses, a valid clock must be present. The minimum low and high periods for the serial clock (SCK)
input are defined as follows:
Low: > 2 CPU clock cycles for fck < 12MHz, 3 CPU clock cycles for fck ≥ 12MHz
High: > 2 CPU clock cycles for fck < 12MHz, 3 CPU clock cycles for fck ≥ 12MHz
5.24.8.1 Serial Programming Algorithm
When writing serial data to the Atmel® ATA6612C/ATA6613C, data is clocked on the rising edge of SCK.
When reading data from the Atmel ATA6612C/ATA6613C, data is clocked on the falling edge of SCK. See Figure 5-127 on
page 269 for timing details.
To program and verify the Atmel ATA6612C/ATA6613C in the serial programming mode, the following sequence is
recommended (see four byte instruction formats in Table 5-129 on page 269):
1. Power-up sequence:
Apply power between VCC and GND while RESET and SCK are set to “0”. In some systems, the programmer can
not guarantee that SCK is held low during power-up.
In this case, RESET must be given a positive pulse of at least two CPU clock cycles duration after SCK has been
set to “0”.
2. Wait for at least 20ms and enable serial programming by sending the programming enable serial instruction to pin
MOSI.
GND
XTAL1
RESET
VCC
AVCC
+2.7V to 5.5V
+2.7V to 5.5V(2)
MOSI
MISO
SCK
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3. The serial programming instructions will not work if the communication is out of synchronization. When in sync.
the second byte (0x53), will echo back when issuing the third byte of the programming enable instruction. Whether
the echo is correct or not, all four bytes of the instruction must be transmitted. If the 0x53 did not echo back, give
RESET a positive pulse and issue a new programming enable command.
4. The flash is programmed one page at a time. The memory page is loaded one byte at a time by supplying the 6
LSB of the address and data together with the load program memory page instruction. To ensure correct loading
of the page, the data low byte must be loaded before data high byte is applied for a given address. The program
memory page is stored by loading the write program memory page instruction with the 8 MSB of the address. If
polling is not used, the user must wait at least tWD_FLASH before issuing the next page
(see Table 5-128 on page 268). Accessing the serial programming interface before the flash write operation
completes can result in incorrect programming.
5. The EEPROM array is programmed one byte at a time by supplying the address and data together with the
appropriate write instruction. An EEPROM memory location is first automatically erased before new data is
written. If polling is not used, the user must wait at least tWD_EEPROM before issuing the next byte
(see Table 5-128 on page 268). In a chip erased device, no 0xFFs in the data file(s) need to be programmed.
6. Any memory location can be verified by using the read instruction which returns the content at the selected
address at serial output MISO.
7. At the end of the programming session, RESET can be set high to commence normal operation.
8. Power-off sequence (if needed):
Set RESET to “1”.
Turn VCC power off.
5.24.8.2 Data Polling Flash
When a page is being programmed into the flash, reading an address location within the page being programmed will give
the value 0xFF. At the time the device is ready for a new page, the programmed value will read correctly. This is used to
determine when the next page can be written. Note that the entire page is written simultaneously and any address within the
page can be used for polling. Data polling of the flash will not work for the value 0xFF, so when programming this value, the
user will have to wait for at least tWD_FLASH before programming the next page. As a chip-erased device contains 0xFF in all
locations, programming of addresses that are meant to contain 0xFF, can be skipped.
See Table 5-128 on page 268 for tWD_FLASH value.
5.24.8.3 Data Polling EEPROM
When a new byte has been written and is being programmed into EEPROM, reading the address location being
programmed will give the value 0xFF. At the time the device is ready for a new byte, the programmed value will read
correctly. This is used to determine when the next byte can be written. This will not work for the value 0xFF, but the user
should have the following in mind: As a chip-erased device contains 0xFF in all locations, programming of addresses that
are meant to contain 0xFF, can be skipped. This does not apply if the EEPROM is re-programmed without chip erasing the
device.
In this case, data polling cannot be used for the value 0xFF, and the user will have to wait at least tWD_EEPROM before
programming the next byte. See Table 5-128 for tWD_EEPROM value.
Table 5-128. Minimum Wait Delay Before Writing the Next Flash or EEPROM Location
Symbol Minimum Wait Delay
tWD_FLASH 4.5ms
tWD_EEPROM 3.6ms
tWD_ERASE 9.0ms
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Figure 5-127. Serial Programming Waveforms
Table 5-129. Serial Programming Instruction Set
Instruction
Instruction Format
OperationByte 1 Byte 2 Byte 3 Byte4
Programming enable 1010 1100 0101 0011 xxxx xxxx xxxx xxxx Enable serial programming after
RESET goes low.
Chip erase 1010 1100 100x xxxx xxxx xxxx xxxx xxxx Chip erase EEPROM and flash.
Read program memory 0010 H000 000a aaaa bbbb bbbb oooo oooo
Read H (high or low) data o from
Program memory at word address
a:b.
Load program memory page 0100 H000 000x xxxx xxbb bbbb iiii iiii
Write H (high or low) data i to
program memory page at word
address b. Data low byte must be
loaded before data high byte is
applied within the same address.
Write program memory page 0100 1100 000a aaaa bbxx xxxx xxxx xxxx Write program memory page at
address a:b.
Read EEPROM memory 1010 0000 000x xxaa bbbb bbbb oooo oooo Read data o from EEPROM memory
at address a:b.
Write EEPROM memory 1100 0000 000x xxaa bbbb bbbb iiii iiii Write data i to EEPROM memory at
address a:b.
Load EEPROM memory
Page (page access) 1100 0001 0000 0000 0000 00bb iiii iiii
Load data i to EEPROM memory
page buffer. After data is loaded,
program EEPROM page.
Write EEPROM memory
Page (page access) 1100 0010 00xx xxaa bbbb bb00 xxxx xxxx Write EEPROM page at address a:b.
Read lock bits 0101 1000 0000 0000 xxxx xxxx xxoo oooo
Read Lock bits. “0” = programmed,
“1” = unprogrammed. See Table 5-
114 on page 253 for details.
Write lock bits 1010 1100 111x xxxx xxxx xxxx 11ii iiii
Write lock bits. Set bits = “0” to
program lock bits. See Table 5-114 on
page 253 for details.
Read signature byte 0011 0000 000x xxxx xxxx xxbb oooo oooo Read signature byte o at address b.
Write fuse bits 1010 1100 1010 0000 xxxx xxxx iiii iiii
Set bits = “0” to program, “1” to
unprogram. See Table XXX on page
XXX for details.
Write fuse high bits 1010 1100 1010 1000 xxxx xxxx iiii iiii
Set bits = “0” to program, “1” to
unprogram. See Table 5-98 on page
229 for details.
Note: a = address high bits, b = address low bits, H = 0 - Low byte, 1 - High Byte, o = data out, i = data in,
x = do not care
SERIAL DATA INPUT
(MOSI)
SERIAL DATA OUTPUT
(MISO)
SERIAL CLOCK INPUT
(SCK)
SAMPLE
MSB LSB
MSB LSB
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5.24.8.4 SPI Serial Programming Characteristics
For characteristics of the SPI module see Section 6.1 “SPI Timing Characteristics” on page 278.
Write extended fuse bits 1010 1100 1010 0100 xxxx xxxx xxxx xxii
Set bits = “0” to program, “1” to
unprogram. See Table 5-117 on page
254 for details.
Read fuse bits 0101 0000 0000 0000 xxxx xxxx oooo oooo
Read fuse bits. “0” = programmed, “1”
= unprogrammed. See Table XXX on
page XXX for details.
Read fuse high bits 0101 1000 0000 1000 xxxx xxxx oooo oooo
Read fuse high bits.
“0”=programmed,
“1” = unprogrammed. See Table 5-98
on page 229 for details.
Read extended fuse bits 0101 0000 0000 1000 xxxx xxxx oooo oooo
Read extended fuse bits. “0” =
programmed, “1” = unprogrammed.
See Table 5-117 on page 254 for
details.
Read calibration byte 0011 1000 000x xxxx 0000 0000 oooo oooo Read calibration byte
Poll RDY/BSY 1111 0000 0000 0000 xxxx xxxx xxxx xxxo
If o = “1”, a programming operation is
still busy. Wait until this bit returns to
“0” before applying another
command.
Table 5-129. Serial Programming Instruction Set (Continued)
Instruction
Instruction Format
OperationByte 1 Byte 2 Byte 3 Byte4
Note: a = address high bits, b = address low bits, H = 0 - Low byte, 1 - High Byte, o = data out, i = data in,
x = do not care
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5.25 Electrical Characteristics
5.25.1 DC Characteristics
Tcase = –40°C to +125°C, VCC = 2.7V to 5.5V (unless otherwise noted)
Parameter Condition Symbol Min.(5) Typ. Max.(5) Units
Input low voltage, except
XTAL1 and reset pin VCC = 2.7V to 5.5V VIL –0.5 0.3VCC(1) V
Input low voltage,
XTAL1 pin VCC = 2.7V to 5.5V VIL1 –0.5 0.1VCC(1) V
Input low voltage, RESET
pin VCC = 2.7V to 5.5V VIL2 –0.5 0.1VCC(1) V
Input high voltage, except
XTAL1 and RESET pins VCC = 2.7V to 5.5V VIH 0.6VCC(2) VCC + 0.5 V
Input high voltage, XTAL1
pin VCC = 2.7V to 5.5V VIH1 0.7VCC(2) VCC + 0.5 V
Input high voltage, RESET
pin VCC = 2.7V to 5.5V VIH2 0.9VCC(2) VCC + 0.5 V
Output low voltage(3) IOL = 20mA, VCC = 5V
IOL = 5mA, VCC = 3V VOL
0.8
0.5 V
Output high voltage(4) IOH = –20mA, VCC = 5V
IOH = –10mA, VCC = 3V VOH
4.1
2.3 V
Input leakage
Current I/O pin
VCC = 5.5V, pin low
(absolute value) IIL 50 nA
Input leakage
Current I/O pin
VCC = 5.5V, pin high
(absolute value) IIH 50 nA
Reset pull-up resistor VCC = 5.0V, VIN = 0V RRST 30 60 kΩ
I/O pin pull-up resistor RPU 20 50 kΩ
Notes: 1. “Max” means the highest value where the pin is guaranteed to be read as low
2. “Min” means the lowest value where the pin is guaranteed to be read as high
3. Although each I/O port can sink more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady
state conditions (non-transient), the following must be observed:
Atmel ATA6612C/ATA6613C:
1] The sum of all IOL, for ports C0 - C5, should not exceed 100mA.
2] The sum of all IOL, for ports C6, D0 - D4, should not exceed 100mA.
3] The sum of all IOL, for ports B0 - B7, D5 - D7, should not exceed 100mA.
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current
greater than the listed test condition.
4. Although each I/O port can source more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady
state conditions (non-transient), the following must be observed:
Atmel ATA6612C/ATA6613C:
1] The sum of all IOH, for ports C0 - C5, should not exceed 100mA.
2] The sum of all IOH, for ports C6, D0 - D4, should not exceed 100mA.
3] The sum of all IOH, for ports B0 - B7, D5 - D7, should not exceed 100mA.
If IOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current
greater than the listed test condition.
5. All DC Characteristics contained in this datasheet are based on actual Atmel ATA6612C microcontrollers
characterization.
6. Values with “Power Reduction REgister - PRR” enabled (0xEF).
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Power supply current(2)
Active 4MHz, VCC = 3V
(ATA6612C/ATA6613CL)
ICC
1.8 3.0 mA
Active 8MHz, VCC = 5V
(ATA6612C/ATA6613C) 6.0 10 mA
Active 15MHz, VCC = 5V
(ATA6612C/ATA6613C) 10.0 16 mA
Idle 4MHz, VCC = 3V
(ATA6612C/ATA6613CV) 0.4 1mA
Idle 8MHz, VCC = 5V
(ATA6612C/ATA6613CL) 1.4 2.4 mA
Idle 15MHz, VCC = 5V
(ATA6612C/ATA6613C) 2.8 4mA
Power-down mode
WDT enabled, VCC = 3V 830 µA
WDT enabled, VCC = 5V 12.6 50 µA
WDT disabled, VCC = 3V 524 µA
WDT disabled, VCC = 5V 6.6 36 µA
Analog comparator
Input offset voltage
VCC = 5V
Vin = VCC/2 VACIO 10 40 mV
Analog comparator
Input leakage current
VCC = 5V
Vin = VCC/2 IACLK –50 50 nA
Analog comparator
propagation delay VCC = 4.5V tACID 140 ns
5.25.1 DC Characteristics (Continued)
Tcase = –40°C to +125°C, VCC = 2.7V to 5.5V (unless otherwise noted)
Parameter Condition Symbol Min.(5) Typ. Max.(5) Units
Notes: 1. “Max” means the highest value where the pin is guaranteed to be read as low
2. “Min” means the lowest value where the pin is guaranteed to be read as high
3. Although each I/O port can sink more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady
state conditions (non-transient), the following must be observed:
Atmel ATA6612C/ATA6613C:
1] The sum of all IOL, for ports C0 - C5, should not exceed 100mA.
2] The sum of all IOL, for ports C6, D0 - D4, should not exceed 100mA.
3] The sum of all IOL, for ports B0 - B7, D5 - D7, should not exceed 100mA.
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current
greater than the listed test condition.
4. Although each I/O port can source more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady
state conditions (non-transient), the following must be observed:
Atmel ATA6612C/ATA6613C:
1] The sum of all IOH, for ports C0 - C5, should not exceed 100mA.
2] The sum of all IOH, for ports C6, D0 - D4, should not exceed 100mA.
3] The sum of all IOH, for ports B0 - B7, D5 - D7, should not exceed 100mA.
If IOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current
greater than the listed test condition.
5. All DC Characteristics contained in this datasheet are based on actual Atmel ATA6612C microcontrollers
characterization.
6. Values with “Power Reduction REgister - PRR” enabled (0xEF).
273
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5.25.2 External Clock Drive Waveforms
Figure 5-128. External Clock Drive Waveforms
5.25.3 External Clock Drive
5.25.4 Maximum Speed versus VCC
Maximum frequency is dependent on VCC. As shown in Figure 5-129, the maximum frequency versus VCC curve is linear
between 2.7V < VCC < 4.5V.
Figure 5-129. Maximum Frequency versus VCC, Atmel ATA6612C/ATA6613C
t
CHCX
V
IH1
V
IL1
t
CHCX
t
CLCH
t
CHCL
t
CLCX
t
CLCL
Table 5-130. External Clock Drive
Parameter Symbol
VCC = 2.7V to 5.5V VCC = 4.5V to 5.5V
UnitsMin. Max. Min. Max.
Oscillator frequency 1/tCLCL 0 8 0 16 MHz
Clock period tCLCL 125 62.5 ns
High time tCHCX 50 25 ns
Low time tCLCX 50 25 ns
Rise time tCLCH 1.6 0.5 µs
Fall time tCHCL 1.6 0.5 µs
Change in period from one
clock cycle to the next ΔtCLCL 2 2 %
Safe Operating Area
2.7V
8MHz
16MHz
5.5V4.5V
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5.26 LIN Re-synchronization Algorithm
5.26.1 Synchronization Algorithm
The possibility to change the value of OSCCAL during the oscillator operation allows for in-situ calibration of the slave node
to entering master frames. The principle of operation is to measure the TBit during the SYNCH byte and to change the
calibration value of OSCCAL to recover from local frequency drifts due to local voltage or temperature deviation. The
algorithm used for the synchronization of the internal RC oscillator is depicted in Figure 5-130.
Figure 5-130. Dichotomic Algorithm Used for LIN Slave Clock Re-synchronization
Decrement
OSCCAL
STOP:
Oscillator
Calibrated
Y
N
N
Measuring
actual TBit
Increment
OSCCAL
-2% < Delta(TBit) < 2%
Delta(TBit) > 2%
Delta(TBit) < -2%
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5.26.2 Precaution Against OSCCAL Discontinuity
The Figure 6-26 on page 288 illustrates the on-purpose discontinuity of RC frequency versus OSCCAL value. For one
correct re-synchronization, the frequency change must be kept on the same side of the discontinuity (no change of
OSCCAL[7]). Since there will be no device having frequency changed by more than 10% (see Figure 6-24 on page 287),
thus no reason to change the frequency value by more than 10%. Therefore, when calibration tries to cross the border
because of subsequent increase (or decrease) in OSCCAL values, then the routine must be stopped.
Example: For parts operating in the lower part of the curve, if New_OSCCAL > 127 then New_OSCCAL = 127. Similar
for parts operating on the high side of the discontinuity.
5.26.2.1 RC Oscillator Precision for LIN Slave implementation
For LIN slave devices, the precision of the RC oscillator before and after re-synchronization are described in the
Table 5-131.
Table 5-131. Oscillator Tolerance Before and After Re-synchronization Algorithm (2.7V < VCC < 5.5V, –40°C to
+125°C)
Parameter Clock Tolerance ΔF/FMaster
FTOL_UNSYNCH
Deviation of slave node clock from the nominal clock rate before
synchronization; relevant for nodes making use of synchronization and direct
SYNCH BREAK detection.
±14.0%
FTOL_SYNCH
Deviation of slave node clock relative to the master node clock after
synchronization; relevant for nodes making use of synchronization; any slave
node must stay within this tolerance for all fields of a frame which follow the
SYNCH FIELD.
Note: For communication between any two nodes their bit rate must
not differ by more than ±2%.
±2.0%
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6. 2-wire Serial Interface Characteristics
Table 6-1 describes the requirements for devices connected to the 2-wire serial bus. The Atmel® ATA6612C/ATA6613C
2-wire serial interface meets or exceeds these requirements under the noted conditions.
Timing symbols refer to Figure 6-1 on page 277.
Table 6-1. 2-wire Serial Bus Requirements
Parameter Condition Symbol Min Max Units
Input low-voltage VIL –0.5 0.3 VCC V
Input high-voltage VIH 0.7 VCC VCC + 0.5 V
Hysteresis of schmitt trigger inputs Vhys(1) 0.05 VCC(2) – V
Output low-voltage 3mA sink current VOL(1) 00.4 V
Rise time for both SDA and SCL tr(1) 20 + 0.1Cb(2,3) 300 ns
Output fall time from VIHmin to VILmax 10pF < Cb < 400pF(3) tof(1) 20 + 0.1Cb(2,3) 250 ns
Spikes suppressed by input filter tSP(1) 050(2) ns
Input current each I/O pin 0.1VCC < Vi < 0.9VCC Ii–10 10 µA
Capacitance for each I/O pin Ci(1) –10 pF
SCL clock frequency fCK(4) > max(16fSCL,
250kHz)(5) fSCL 0400 kHz
Value of pull-up resistor
fSCL ≤ 100kHz
Rp
Ω
fSCL > 100kHz Ω
Hold time (repeated) START condition fSCL ≤ 100kHz tHD;STA
4.0 –µs
fSCL > 100kHz 0.6 –µs
Low period of the SCL clock fSCL ≤ 100kHz(6)
tLOW
4.7 –µs
fSCL > 100kHz(7) 1.3 –µs
High period of the SCL clock fSCL ≤ 100kHz tHIGH
4.0 –µs
fSCL > 100kHz 0.6 –µs
Set-up time for a repeated START
condition
fSCL ≤ 100kHz tSU;STA
4.7 –µs
fSCL > 100kHz 0.6 –µs
Data hold time fSCL ≤ 100kHz tHD;DAT
03.45 µs
fSCL > 100kHz 00.9 µs
Data setup time fSCL ≤ 100kHz tSU;DAT
250 –ns
fSCL > 100kHz 100 –ns
Notes: 1. In Atmel ATA6612C/ATA6613C, this parameter is characterized and not 100% tested.
2. Required only for fSCL > 100kHz.
3. Cb = capacitance of one bus line in pF.
4. fCK = CPU clock frequency
5. This requirement applies to all Atmel ATA6612C/ATA6613C 2-wire serial interface operation. Other devices
connected to the 2-wire serial bus need only obey the general fSCL requirement.
6. The actual low period generated by the Atmel ATA6612C/ATA6613C 2-wire serial interface is (1/fSCL – 2/fCK),
thus fCK must be greater than 6MHz for the low time requirement to be strictly met at fSCL = 100kHz.
7. The actual low period generated by the Atmel ATA6612C/ATA6613C 2-wire serial interface is (1/fSCL – 2/fCK),
thus the low time requirement will not be strictly met for fSCL > 308kHz when fCK = 8MHz. Still, Atmel
ATA6612C/ATA6613C devices connected to the bus may communicate at full speed (400kHz) with other
Atmel ATA6612C/ATA6613C devices, as well as any other device with a proper tLOW acceptance margin.
VCC 0,4V–
3mA
----------------------------
1000ns
Cb
-----------------
VCC 0,4V–
3mA
----------------------------
300ns
Cb
--------------
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Figure 6-1. 2-wire Serial Bus Timing
Setup time for STOP condition fSCL ≤ 100kHz tSU;STO
4.0 –µs
fSCL > 100kHz 0.6 –µs
Bus free time between a STOP and
START condition
fSCL ≤ 100kHz tBUF
4.7 –µs
fSCL > 100kHz 1.3 –µs
Table 6-1. 2-wire Serial Bus Requirements (Continued)
Parameter Condition Symbol Min Max Units
Notes: 1. In Atmel ATA6612C/ATA6613C, this parameter is characterized and not 100% tested.
2. Required only for fSCL > 100kHz.
3. Cb = capacitance of one bus line in pF.
4. fCK = CPU clock frequency
5. This requirement applies to all Atmel ATA6612C/ATA6613C 2-wire serial interface operation. Other devices
connected to the 2-wire serial bus need only obey the general fSCL requirement.
6. The actual low period generated by the Atmel ATA6612C/ATA6613C 2-wire serial interface is (1/fSCL – 2/fCK),
thus fCK must be greater than 6MHz for the low time requirement to be strictly met at fSCL = 100kHz.
7. The actual low period generated by the Atmel ATA6612C/ATA6613C 2-wire serial interface is (1/fSCL – 2/fCK),
thus the low time requirement will not be strictly met for fSCL > 308kHz when fCK = 8MHz. Still, Atmel
ATA6612C/ATA6613C devices connected to the bus may communicate at full speed (400kHz) with other
Atmel ATA6612C/ATA6613C devices, as well as any other device with a proper tLOW acceptance margin.
tof
tSU,STA tHD,STA tSU,STO
tBUF
tHD,DAT tSU,DAT
tHIGH
tLOW tLOW
SCL
SDA
tr
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6.1 SPI Timing Characteristics
See Figure 6-2 and Figure 6-3 on page 279 for details.
Figure 6-2. SPI Interface Timing Requirements (Master Mode)
Table 6-2. SPI Timing Parameters
Description Mode Min Typ Max
1SCK period Master See Table 5-70 on page 162
ns
2SCK high/low Master 50% duty cycle
3Rise/fall time Master 3.6
4Setup Master 10
5Hold Master 10
6Out to SCK Master 0.5 × tsck
7SCK to out Master 10
8SCK to out high Master 10
9SS low to out Slave 15
10 SCK period Slave 4 × tck
11 SCK high/low(1) Slave 2 × tck
12 Rise/fall time Slave 1600
13 Setup Slave 10
14 Hold Slave tck
15 SCK to out Slave 15
16 SCK to SS high Slave 20
17 SS high to tri-state Slave 10
18 SS low to SCK Slave 20
Note: 1. In SPI programming mode the minimum SCK high/low period is:
- 2 tCLCL for fCK < 12MHz
- 3 tCLCL for fCK > 12MHz
6
MSB
SS
SCK
(CPOL = 0)
SCK
(CPOL = 1)
MISO
(Data Input)
MOSI
(Data Output) MSB LSB
LSB
...
...
45
8
7
1
22
3
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ATA6612C/ATA6613C [DATASHEET]
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Figure 6-3. SPI Interface Timing Requirements (Slave Mode)
6.2 ADC Characteristics
9
MSB
SS
SCK
(CPOL = 0)
SCK
(CPOL = 1)
MOSI
(Data Input)
MISO
(Data Output) MSB LSB X
LSB
...
...
13 14
17
15
10 16
11 11
12
Table 6-3. ADC Characteristics
Parameter Condition Symbol Min Typ Max Units
Resolution 10 Bits
Absolute accuracy (including
INL, DNL, quantization error,
gain and offset error)
VREF = 4V, VCC = 4V,
ADC clock = 200kHz 23.5 LSB
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
Noise reduction mode
23.5 LSB
Integral non-linearity (INL) VREF = 4V, VCC = 4V,
ADC clock = 200kHz 0.6 2.5 LSB
Differential non-linearity (DNL) VREF = 4V, VCC = 4V,
ADC clock = 200kHz 0.40 1.0 LSB
Gain error VREF = 4V, VCC = 4V,
ADC clock = 200kHz –3.5 –1.3 3.5 LSB
Offset error VREF = 4V, VCC = 4V,
ADC clock = 200kHz 1.8 3.5 LSB
Conversion time Free running conversion 13 cycles µs
Clock frequency 50 200 kHz
Analog supply voltage AVCC VCC – 0.3 VCC + 0.3 V
Reference voltage VREF 1.0 AVCC V
Input voltage VIN GND VREF V
Internal voltage reference VINT 1.0 1.1 1.2 V
Reference input resistance RREF 22.4 32 41.6 kΩ
Analog input resistance RAIN 100 MΩ
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6.3 Atmel ATA6612C/ATA6613C Typical Characteristics
Note: Values of temp refer to Tcase.
6.3.1 Active Supply Current
Figure 6-4. Active Supply Current versus Frequency (1MHz to 20MHz), Temp = 125°C
Figure 6-5. Idle Supply Current versus Frequency (1MHz to 20MHz), Temp = 125°C
02468101214161820
Frequency (MHz)
14
16
18
20
12
10
8
6
4
2
0
ICC (mA)
5.5V
5.0V
4.5V
3.3V
3.0V
2.7V
0 2 4 6 8 101214161820
Frequency (MHz)
6
4
2
0
ICC (mA)
5.5V
5.0V
4.5V
3.3V
3.0V
2.7V
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6.3.1.1 Power-down Supply Current
Figure 6-6. Power-down Supply Current versus VCC (Watchdog Timer Disabled)
Figure 6-7. Power-down Supply Current versus VCC (Watchdog Timer Enabled)
5
6
4
3
2
1
0
7
8
ICC (µA)
33.5 44.555.5
VCC (V)
125
85
25
-40
5
6
4
3
2
1
0
7
8
I
CC
(µA)
32.5 3.5 44.555.5
V
CC
(V)
125
85
25
-40
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6.3.1.2 Pin Pull-up
Figure 6-8. I/O Pin Pull-up Resistor Current versus Input Voltage (VCC = 5V)
Figure 6-9. Output Low Voltage versus Output Low Current (VCC = 5V)
Figure 6-10. Output Low Voltage versus Output Low Current (VCC = 3V)
140
160
120
100
80
60
40
20
0
IOP (µA)
01 32456
VOP (V)
125
-40
0246810
12 14 16 18 20
V
OL
(V)
I
OL
(mA)
0.7
0.8
0.6
0.5
0.4
0.3
0.2
0.1
0
125°C
85°C
25°C
-40°C
02 4 6 810
12 14 16 18 20
VOL (V)
IOL (mA)
1.0
1.2
0.8
0.6
0.4
0.2
0
125°C
85°C
25°C
-40°C
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Figure 6-11. Output High Voltage versus Output High Current (VCC = 5V)
Figure 6-12. Output High Voltage versus Output High Current (VCC = 3V)
Figure 6-13. Reset Pull-Up Resistor Current versus Reset Pin Voltage (VCC = 5V)
0246810
12 14 16 18 20
IOH (mA)
VOH (V)
5
5.2
4.8
4.6
4.4
4.2
4
125°C
85°C
25°C
-40°C
02 4 6 810
12 14 16 18 20
IOH (mA)
Current (V)
3.5
3
2.5
2
1.5
1
0.5
0
125°C
25°C
85°C
-40°C
140
160
120
100
80
60
40
20
0
IOP (µA)
01 32 456
VOP (V)
125
-40
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6.3.1.3 Pin Driver Strength
Figure 6-14. Output Low Voltage versus Output Low Current (VCC = 5V)
Figure 6-15. Output Low Voltage versus Output Low Current (VCC = 3V)
Figure 6-16. Output High Voltage versus Output High Current (VCC = 5V)
0246810
12 14 16 18 20
VOL (V)
IOL (mA)
0.7
0.8
0.6
0.5
0.4
0.3
0.2
0.1
0
125°C
85°C
25°C
-40°C
02 4 6 810
12 14 16 18 20
VOL (V)
IOL (mA)
1.0
1.2
0.8
0.6
0.4
0.2
0
125°C
85°C
25°C
-40°C
0246810
12 14 16 18 20
IOH (mA)
VOH (V)
5
5.2
4.8
4.6
4.4
4.2
4
125°C
85°C
25°C
-40°C
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Figure 6-17. Output High Voltage versus Output High Current (VCC = 3V)
6.3.1.4 Pin Thresholds and Hysteresis
Figure 6-18. I/O Pin Input Threshold versus VCC (VIH, I/O Pin Read as 1)
Figure 6-19. I/O Pin Input Threshold versus VCC (VIL, I/O Pin Read as 0)
02 4 6 810
12 14 16 18 20
IOH (mA)
Current (V)
3.5
3
2.5
2
1.5
1
0.5
0
125°C
25°C
85°C
-40°C
3
3.5
2.5
2
1.5
0
Vih (V)
2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
125
85
25
-40
3
2.5
2
1.5
1
0.5
0
Vil (V)
22.5 3.53 4 4.5 5 5.5 6
VCC (V)
125 °C
-40 °C
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Figure 6-20. Reset Input Threshold Voltage versus VCC (VIH, Reset Pin Read as 1)
Figure 6-21. Reset Input Threshold Voltage versus VCC (VIL, Reset Pin Read as 0)
6.3.1.5 Internal Oscillator Speed
Figure 6-22. Watchdog Oscillator Frequency versus VCC
2 2.5 3 3.5 4 4.5 55.5
VCC (V)
Threshold (V)
2.5
3
2
1.5
1
0.5
0
125°C
85°C
25°C
-40°C
3.5
4
2 2.5 3 3.5 4 4.5 55.5
VCC (V)
-40°C
25°C
85°C
125°C
Threshold (V)
2.5
2
1.5
1
0.5
0
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
FRC (kHz)
120
122
118
116
128
130
126
124
114
112
110
125°C
85°C
25°C
-40°C
287
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
Figure 6-23. Calibrated 8MHz RC Oscillator Frequency versus Temperature
Figure 6-24. Calibrated 8MHz RC Oscillator Frequency versus VCC
Figure 6-25. Calibrated 8MHz RC Oscillator Frequency versus OSCAL Value (for ATA6613C)
8.3
8.4
5.0V
2.7V
8.2
8.1
8.0
7.9
7.8
7.7
7.6
FRC (MHz)
-40 -30 -10-20 0 10 20 30 40 6050 70 80 90 100 110 120
Temperature
125°C
85°C
25°C
-40°C
8.2
8.4
8
7.8
7.6
7.4
7.2
7
FRC (MHz)
VCC (V)
2.5 3 3.5 4 4.5 5 5.5
125°C
85°C
25°C
-40°C
14
16
12
10
8
6
4
2
FRC (MHz)
016 4832 64 80 96 112 128 160144 176 192 208 224 240
OSCCAL (X1)
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
288
Figure 6-26. Calibrated 8MHz RC Oscillator Frequency versus OSCAL Value (for Atmel ATA6612C only)
6.3.1.6 BOD Thresholds and Analog Comparator Offset
Figure 6-27. BOD Threshold versus Temperature (BODLEVEL is 4.0V)
Figure 6-28. BOD Threshold versus Temperature (BODLEVEL is 2.7V)
125°C
85°C
25°C
-40°C
14
12
10
8
6
4
2
FRC (MHz)
016 4832 64 80 96 112 128 160144 176 192 208 224 240
OSCCAL (X1)
4.6
4.5
4.4
4.3
4.2
4.1
4
Threshold (V)
-55 -45 -25-35 -15 -5 5 15 25 4535 55 65 75 85 95 105 115 125
Temperature (°C)
Rising VCC
Falling VCC
3
2.9
2.8
2.7
2.6
2.5
2.4
Threshold (V)
-50 -40 -20-30 -10 0 10 20 30 5040 60 70 80 90 100 110 120
Temperature (°C)
Rising VCC
Falling VCC
289
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
Figure 6-29. Bandgap Voltage versus VCC
6.3.1.7 Peripheral Units
Figure 6-30. Analog to Digital Converter GAIN versus VCC
Figure 6-31. Analog to Digital Converter OFFSET versus VCC
85°C
25°C
125°C
-40°C
1.1
1.095
1.09
1.085
1.08
1.075
Bandgap Voltage (V)
VCC (V)
2.5 3 3.5 4 4.5 5 5.5
-0.8
-0.6
-1.0
-0.2
0
-0.4
-1.2
-1.4
-1.6
Error (LSB)
-50 0 50 100 150
4V IDLE
4V STD
Temperature
1.5
1.0
2.5
2.0
0.5
0
Error (LSB)
4V IDLE
4V STD
-50 0 50 100 150
Temperature
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
290
Figure 6-32. Analog to Digital Converter DNL versus VCC
Figure 6-33. Analog to Digital Converter INL versus VCC
0.20
0.25
0.15
0.35
0.40
0.30
0.10
0.05
0
Error (LSB)
4V IDLE
4V STD
-50 0 50 100 150
Temperature
0.4
0.5
0.3
0.7
0.6
0.2
0.1
0
Error (LSB)
4V IDLE
4V STD
-50 0 50 100 150
Temperature
291
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
6.4 Register Summary
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
(0xFF) Reserved – – – – – – – –
(0xFE) Reserved – – – – – – – –
(0xFD) Reserved – – – – – – – –
(0xFC) Reserved – – – – – – – –
(0xFB) Reserved – – – – – – – –
(0xFA) Reserved – – – – – – – –
(0xF9) Reserved – – – – – – – –
(0xF8) Reserved – – – – – – – –
(0xF7) Reserved – – – – – – – –
(0xF6) Reserved – – – – – – – –
(0xF5) Reserved – – – – – – – –
(0xF4) Reserved – – – – – – – –
(0xF3) Reserved – – – – – – – –
(0xF2) Reserved – – – – – – – –
(0xF1) Reserved – – – – – – – –
(0xF0) Reserved – – – – – – – –
(0xEF) Reserved – – – – – – – –
(0xEE) Reserved – – – – – – – –
(0xED) Reserved – – – – – – – –
(0xEC) Reserved – – – – – – – –
(0xEB) Reserved – – – – – – – –
(0xEA) Reserved – – – – – – – –
(0xE9) Reserved – – – – – – – –
(0xE8) Reserved – – – – – – – –
(0xE7) Reserved – – – – – – – –
(0xE6) Reserved – – – – – – – –
(0xE5) Reserved – – – – – – – –
(0xE4) Reserved – – – – – – – –
(0xE3) Reserved – – – – – – – –
(0xE2) Reserved – – – – – – – –
(0xE1) Reserved – – – – – – – –
(0xE0) Reserved – – – – – – – –
(0xDF) Reserved – – – – – – – –
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
2. I/O registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In
these registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and
SBI instructions will only operate on the specified bit, and can therefore be used on registers containing such status
flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing
I/O registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The Atmel
ATA6612C/ATA6613C is a complex microcontroller with more peripheral units than can be supported within the 64
location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from 0x60 - 0xFF in SRAM,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
5. Only valid for Atmel ATA6612C/ATA6613C
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
292
(0xDE) Reserved – – – – – – – –
(0xDD) Reserved – – – – – – – –
(0xDC) Reserved – – – – – – – –
(0xDB) Reserved – – – – – – – –
(0xDA) Reserved – – – – – – – –
(0xD9) Reserved – – – – – – – –
(0xD8) Reserved – – – – – – – –
(0xD7) Reserved – – – – – – – –
(0xD6) Reserved – – – – – – – –
(0xD5) Reserved – – – – – – – –
(0xD4) Reserved – – – – – – – –
(0xD3) Reserved – – – – – – – –
(0xD2) Reserved – – – – – – – –
(0xD1) Reserved – – – – – – – –
(0xD0) Reserved – – – – – – – –
(0xCF) Reserved – – – – – – – –
(0xCE) Reserved – – – – – – – –
(0xCD) Reserved – – – – – – – –
(0xCC) Reserved – – – – – – – –
(0xCB) Reserved – – – – – – – –
(0xCA) Reserved – – – – – – – –
(0xC9) Reserved – – – – – – – –
(0xC8) Reserved – – – – – – – –
(0xC7) Reserved – – – – – – – –
(0xC6) UDR0 USART I/O data register 180
(0xC5) UBRR0H USART baud rate register high 183
(0xC4) UBRR0L USART baud rate register low 183
(0xC3) Reserved – – – – – – – –
(0xC2) UCSR0C UMSEL01 UMSEL00 UPM01 UPM00 USBS0 UCSZ01
/UDORD0
UCSZ00 /
UCPHA0 UCPOL0 182/191
(0xC1) UCSR0B RXCIE0 TXCIE0 UDRIE0 RXEN0 TXEN0 UCSZ02 RXB80 TXB80 181
(0xC0) UCSR0A RXC0 TXC0 UDRE0 FE0 DOR0 UPE0 U2X0 MPCM0 180
(0xBF) Reserved – – – – – – – –
(0xBE) Reserved – – – – – – – –
6.4 Register Summary (Continued)
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
2. I/O registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In
these registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and
SBI instructions will only operate on the specified bit, and can therefore be used on registers containing such status
flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing
I/O registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The Atmel
ATA6612C/ATA6613C is a complex microcontroller with more peripheral units than can be supported within the 64
location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from 0x60 - 0xFF in SRAM,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
5. Only valid for Atmel ATA6612C/ATA6613C
293
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
(0xBD) TWAMR TWAM6 TWAM5 TWAM4 TWAM3 TWAM2 TWAM1 TWAM0 – 202
(0xBC) TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN –TWIE200
(0xBB) TWDR 2-wire serial interface data register 201
(0xBA) TWAR TWA6 TWA5 TWA4 TWA3 TWA2 TWA1 TWA0 TWGCE 202
(0xB9) TWSR TWS7 TWS6 TWS5 TWS4 TWS3 – TWPS1 TWPS0 201
(0xB8) TWBR 2-wire serial interface bit rate register 199
(0xB7) Reserved – – – – – – –
(0xB6) ASSR – EXCLK AS2 TCN2UB OCR2AUB OCR2BUB TCR2AUB TCR2BUB 154
(0xB5) Reserved – – – – – – – –
(0xB4) OCR2B Timer/counter2 output compare register B 151
(0xB3) OCR2A Timer/counter2 output compare register A 151
(0xB2) TCNT2 Timer/counter2 (8-bit) 151
(0xB1) TCCR2B FOC2A FOC2B –– WGM22 CS22 CS21 CS20 150
(0xB0) TCCR2A COM2A1 COM2A0 COM2B1 COM2B0 ––WGM21WGM20 148
(0xAF) Reserved – – – – – – – –
(0xAE) Reserved – – – – – – – –
(0xAD) Reserved – – – – – – – –
(0xAC) Reserved – – – – – – – –
(0xAB) Reserved – – – – – – – –
(0xAA) Reserved – – – – – – – –
(0xA9) Reserved – – – – – – – –
(0xA8) Reserved – – – – – – – –
(0xA7) Reserved – – – – – – – –
(0xA6) Reserved – – – – – – – –
(0xA5) Reserved – – – – – – – –
(0xA4) Reserved – – – – – – – –
(0xA3) Reserved – – – – – – – –
(0xA2) Reserved – – – – – – – –
(0xA1) Reserved – – – – – – – –
(0xA0) Reserved – – – – – – – –
(0x9F) Reserved – – – – – – – –
(0x9E) Reserved – – – – – – – –
(0x9D) Reserved – – – – – – – –
(0x9C) Reserved – – – – – – – –
6.4 Register Summary (Continued)
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
2. I/O registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In
these registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and
SBI instructions will only operate on the specified bit, and can therefore be used on registers containing such status
flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing
I/O registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The Atmel
ATA6612C/ATA6613C is a complex microcontroller with more peripheral units than can be supported within the 64
location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from 0x60 - 0xFF in SRAM,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
5. Only valid for Atmel ATA6612C/ATA6613C
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
294
(0x9B) Reserved – – – – – – – –
(0x9A) Reserved – – – – – – – –
(0x99) Reserved – – – – – – – –
(0x98) Reserved – – – – – – – –
(0x97) Reserved – – – – – – – –
(0x96) Reserved – – – – – – – –
(0x95) Reserved – – – – – – – –
(0x94) Reserved – – – – – – – –
(0x93) Reserved – – – – – – – –
(0x92) Reserved – – – – – – – –
(0x91) Reserved – – – – – – – –
(0x90) Reserved – – – – – – – –
(0x8F) Reserved – – – – – – – –
(0x8E) Reserved – – – – – – – –
(0x8D) Reserved – – – – – – – –
(0x8C) Reserved – – – – – – – –
(0x8B) OCR1BH Timer/counter1 - output compare register B high byte 135
(0x8A) OCR1BL Timer/counter1 - output compare register B low byte 135
(0x89) OCR1AH Timer/counter1 - output compare register A high byte 135
(0x88) OCR1AL Timer/counter1 - output compare register A low byte 135
(0x87) ICR1H Timer/counter1 - input capture register high byte 136
(0x86) ICR1L Timer/counter1 - input capture register low byte 136
(0x85) TCNT1H Timer/counter1 - counter register high byte 135
(0x84) TCNT1L Timer/counter1 - counter register low byte 135
(0x83) Reserved – – – – – – – –
(0x82) TCCR1C FOC1A FOC1B – – – – – – 135
(0x81) TCCR1B ICNC1 ICES1 – WGM13 WGM12 CS12 CS11 CS10 134
(0x80) TCCR1A COM1A1 COM1A0 COM1B1 COM1B0 ––WGM11WGM10 132
(0x7F) DIDR1 – – – – – –AIN1DAIN0D 223
(0x7E) DIDR0 – – ADC5D ADC4D ADC3D ADC2D ADC1D ADC0D 238
(0x7D) Reserved – – – – – – – –
(0x7C) ADMUX REFS1 REFS0 ADLAR – MUX3 MUX2 MUX1 MUX0 235
(0x7B) ADCSRB –ACME– – – ADTS2 ADTS1 ADTS0 238
(0x7A) ADCSRA ADEN ADSC ADATE ADIF ADIE ADPS2 ADPS1 ADPS0 236
6.4 Register Summary (Continued)
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
2. I/O registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In
these registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and
SBI instructions will only operate on the specified bit, and can therefore be used on registers containing such status
flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing
I/O registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The Atmel
ATA6612C/ATA6613C is a complex microcontroller with more peripheral units than can be supported within the 64
location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from 0x60 - 0xFF in SRAM,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
5. Only valid for Atmel ATA6612C/ATA6613C
295
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
(0x79) ADCH ADC data register high byte 237
(0x78) ADCL ADC data register low byte 237
(0x77) Reserved – – – – – – – –
(0x76) Reserved – – – – – – – –
(0x75) Reserved – – – – – – – –
(0x74) Reserved – – – – – – – –
(0x73) Reserved – – – – – – – –
(0x72) Reserved – – – – – – – –
(0x71) Reserved – – – – – – – –
(0x70) TIMSK2 – – – – – OCIE2B OCIE2A TOIE2 152
(0x6F) TIMSK1 ––ICIE1 –– OCIE1B OCIE1A TOIE1 136
(0x6E) TIMSK0 – – – – – OCIE0B OCIE0A TOIE0 111
(0x6D) PCMSK2 PCINT23 PCINT22 PCINT21 PCINT20 PCINT19 PCINT18 PCINT17 PCINT16 96
(0x6C) PCMSK1 – PCINT14 PCINT13 PCINT12 PCINT11 PCINT10 PCINT9 PCINT8 96
(0x6B) PCMSK0 PCINT7 PCINT6 PCINT5 PCINT4 PCINT3 PCINT2 PCINT1 PCINT0 96
(0x6A) Reserved – – – – – – – –
(0x69) EICRA – – – – ISC11 ISC10 ISC01 ISC00 93
(0x68) PCICR – – – – – PCIE2 PCIE1 PCIE0
(0x67) Reserved – – – – – – – –
(0x66) OSCCAL Oscillator Calibration Register 52
(0x65) Reserved – – – – – – – –
(0x64) PRR PRTWI PRTIM2 PRTIM0 – PRTIM1 PRSPI PRUSAR0 PRADC 58
(0x63) Reserved – – – – – – – –
(0x62) Reserved – – – – – – – –
(0x61) CLKPR CLKPCE – – – CLKPS3 CLKPS2 CLKPS1 CLKPS0 54
(0x60) WDTCSR WDIF WDIE WDP3 WDCE WDE WDP2 WDP1 WDP0 68
0x3F (0x5F) SREG I T H S V N Z C 33
0x3E (0x5E) SPH – – – – – (SP10)(5) SP9 SP8 35
0x3D (0x5D) SPL SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 35
0x3C (0x5C) Reserved – – – – – – – –
0x3B (0x5B) Reserved – – – – – – – –
0x3A (0x5A) Reserved – – – – – – – –
0x39 (0x59) Reserved – – – – – – – –
0x38 (0x58) Reserved – – – – – – – –
6.4 Register Summary (Continued)
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
2. I/O registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In
these registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and
SBI instructions will only operate on the specified bit, and can therefore be used on registers containing such status
flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing
I/O registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The Atmel
ATA6612C/ATA6613C is a complex microcontroller with more peripheral units than can be supported within the 64
location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from 0x60 - 0xFF in SRAM,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
5. Only valid for Atmel ATA6612C/ATA6613C
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
296
0x37 (0x57) SPMCSR SPMIE (RWWSB)5. –(RWWSRE)
(5) BLBSET PGWRT PGERS SELFPRGEN 244
0x36 (0x56) Reserved – – – – – – – –
0x35 (0x55) MCUCR – – –PUD–– IVSEL IVCE
0x34 (0x54) MCUSR – – – – WDRF BORF EXTRF PORF
0x33 (0x53) SMCR – – – – SM2 SM1 SM0 SE 56
0x32 (0x52) Reserved – – – – – – – –
0x31 (0x51) Reserved – – – – – – – –
0x30 (0x50) ACSR ACD ACBG ACO ACI ACIE ACIC ACIS1 ACIS0 222
0x2F (0x4F) Reserved – – – – – – – –
0x2E (0x4E) SPDR SPI data register 163
0x2D (0x4D) SPSR SPIF WCOL – – – – – SPI2X 162
0x2C (0x4C) SPCR SPIE SPE DORD MSTR CPOL CPHA SPR1 SPR0 161
0x2B (0x4B) GPIOR2 General purpose I/O register 2 45
0x2A (0x4A) GPIOR1 General purpose I/O register 1 45
0x29 (0x49) Reserved – – – – – – – –
0x28 (0x48) OCR0B Timer/counter0 output compare register B
0x27 (0x47) OCR0A Timer/counter0 output compare register A
0x26 (0x46) TCNT0 Timer/counter0 (8-bit)
0x25 (0x45) TCCR0B FOC0A FOC0B –– WGM02 CS02 CS01 CS00
0x24 (0x44) TCCR0A COM0A1 COM0A0 COM0B1 COM0B0 ––WGM01WGM00
0x23 (0x43) GTCCR TSM – – – – – PSRASY PSRSYNC 113/156
0x22 (0x42) EEARH (EEPROM address register high byte)5. 41
0x21 (0x41) EEARL EEPROM address register low byte 41
0x20 (0x40) EEDR EEPROM data register 41
0x1F (0x3F) EECR –– EEPM1 EEPM0 EERIE EEMPE EEPE EERE 41
0x1E (0x3E) GPIOR0 General purpose I/O register 0 45
0x1D (0x3D) EIMSK – – – – – – INT1 INT0 94
0x1C (0x3C) EIFR – – – – – – INTF1 INTF0 94
0x1B (0x3B) PCIFR – – – – – PCIF2 PCIF1 PCIF0
0x1A (0x3A) Reserved – – – – – – – –
0x19 (0x39) Reserved – – – – – – – –
0x18 (0x38) Reserved – – – – – – – –
0x17 (0x37) TIFR2 – – – – –OCF2BOCF2ATOV2 152
0x16 (0x36) TIFR1 ––ICF1 ––OCF1BOCF1ATOV1 137
6.4 Register Summary (Continued)
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
2. I/O registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In
these registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and
SBI instructions will only operate on the specified bit, and can therefore be used on registers containing such status
flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing
I/O registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The Atmel
ATA6612C/ATA6613C is a complex microcontroller with more peripheral units than can be supported within the 64
location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from 0x60 - 0xFF in SRAM,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
5. Only valid for Atmel ATA6612C/ATA6613C
297
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
0x15 (0x35) TIFR0 – – – – –OCF0BOCF0ATOV0
0x14 (0x34) Reserved – – – – – – – –
0x13 (0x33) Reserved – – – – – – – –
0x12 (0x32) Reserved – – – – – – – –
0x11 (0x31) Reserved – – – – – – – –
0x10 (0x30) Reserved – – – – – – – –
0x0F (0x2F) Reserved – – – – – – – –
0x0E (0x2E) Reserved – – – – – – – –
0x0D (0x2D) Reserved – – – – – – – –
0x0C (0x2C) Reserved – – – – – – – –
0x0B (0x2B) PORTD PORTD7 PORTD6 PORTD5 PORTD4 PORTD3 PORTD2 PORTD1 PORTD0 92
0x0A (0x2A) DDRD DDD7 DDD6 DDD5 DDD4 DDD3 DDD2 DDD1 DDD0 92
0x09 (0x29) PIND PIND7 PIND6 PIND5 PIND4 PIND3 PIND2 PIND1 PIND0 92
0x08 (0x28) PORTC – PORTC6 PORTC5 PORTC4 PORTC3 PORTC2 PORTC1 PORTC0 91
0x07 (0x27) DDRC – DDC6 DDC5 DDC4 DDC3 DDC2 DDC1 DDC0 91
0x06 (0x26) PINC – PINC6 PINC5 PINC4 PINC3 PINC2 PINC1 PINC0 92
0x05 (0x25) PORTB PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 91
0x04 (0x24) DDRB DDB7 DDB6 DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 91
0x03 (0x23) PINB PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 91
0x02 (0x22) Reserved – – – – – – – –
0x01 (0x21) Reserved – – – – – – – –
0x0 (0x20) Reserved – – – – – – – –
6.4 Register Summary (Continued)
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
2. I/O registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In
these registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and
SBI instructions will only operate on the specified bit, and can therefore be used on registers containing such status
flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing
I/O registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The Atmel
ATA6612C/ATA6613C is a complex microcontroller with more peripheral units than can be supported within the 64
location reserved in Opcode for the IN and OUT instructions. For the extended I/O space from 0x60 - 0xFF in SRAM,
only the ST/STS/STD and LD/LDS/LDD instructions can be used.
5. Only valid for Atmel ATA6612C/ATA6613C
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
298
6.5 Instruction Set Summary
Mnemonics Operands Description Operation Flags #Clocks
Arithmetic and Logic Instructions
ADD Rd, Rr Add two registers Rd ← Rd + Rr Z,C,N,V,H 1
ADC Rd, Rr Add with carry two registers Rd ← Rd + Rr + C Z,C,N,V,H 1
ADIW Rdl,K Add immediate to word Rdh:Rdl ← Rdh:Rdl + K Z,C,N,V,S 2
SUB Rd, Rr Subtract two registers Rd ← Rd – Rr Z,C,N,V,H 1
SUBI Rd, K Subtract constant from register Rd ← Rd – K Z,C,N,V,H 1
SBC Rd, Rr Subtract with carry two registers Rd ← Rd – Rr – C Z,C,N,V,H 1
SBCI Rd, K Subtract with carry constant from reg. Rd ← Rd – K – C Z,C,N,V,H 1
SBIW Rdl,K Subtract immediate from word Rdh:Rdl ← Rdh:Rdl – K Z,C,N,V,S 2
AND Rd, Rr Logical AND registers Rd ← Rd × Rr Z,N,V 1
ANDI Rd, K Logical AND register and constant Rd ← Rd × KZ,N,V 1
OR Rd, Rr Logical OR registers Rd ← Rd v Rr Z,N,V 1
ORI Rd, K Logical OR register and constant Rd ← Rd v K Z,N,V 1
EOR Rd, Rr Exclusive OR registers Rd ← Rd ⊕ Rr Z,N,V 1
COM Rd One’s complement Rd ← 0xFF − Rd Z,C,N,V 1
NEG Rd Two’s complement Rd ← 0x00 − Rd Z,C,N,V,H 1
SBR Rd,K Set bit(s) in register Rd ← Rd v K Z,N,V 1
CBR Rd,K Clear bit(s) in register Rd ← Rd × (0xFF – K) Z,N,V 1
INC Rd Increment Rd ← Rd + 1 Z,N,V 1
DEC Rd Decrement Rd ← Rd − 1 Z,N,V 1
TST Rd Test for zero or minus Rd ← Rd × Rd Z,N,V 1
CLR Rd Clear register Rd ← Rd ⊕ Rd Z,N,V 1
SER Rd Set register Rd ← 0xFF None 1
MUL Rd, Rr Multiply unsigned R1:R0 ← Rd × Rr Z,C 2
MULS Rd, Rr Multiply signed R1:R0 ← Rd × Rr Z,C 2
MULSU Rd, Rr Multiply signed with unsigned R1:R0 ← Rd × Rr Z,C 2
FMUL Rd, Rr Fractional multiply unsigned R1:R0 ← (Rd × Rr) << 1 Z,C 2
FMULS Rd, Rr Fractional multiply signed R1:R0 ← (Rd × Rr) << 1 Z,C 2
FMULSU Rd, Rr Fractional multiply signed with unsigned R1:R0 ← (Rd × Rr) << 1 Z,C 2
Branch Instructions
RJMP kRelative jump PC ← PC + k + 1 None 2
IJMP Indirect jump to (Z) PC ← Z None 2
JMP(1) kDirect jump PC ← k None 3
RCALL kRelative subroutine call PC ← PC + k + 1 None 3
ICALL Indirect call to (Z) PC ← Z None 3
CALL(1) kDirect subroutine call PC ← k None 4
RET Subroutine return PC ← STACK None 4
RETI Interrupt return PC ← STACK I 4
CPSE Rd,Rr Compare, skip if equal if (Rd = Rr) PC ← PC + 2 or 3 None 1/2/3
CP Rd,Rr Compare Rd − Rr Z, N,V,C,H 1
CPC Rd,Rr Compare with carry Rd − Rr − C Z, N,V,C,H 1
Note: 1. These instructions are only available in ATA6613C
299
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
CPI Rd,K Compare register with immediate Rd − K Z, N,V,C,H 1
SBRC Rr, b Skip if bit in register cleared if (Rr(b)=0) PC ← PC + 2 or 3 None 1/2/3
SBRS Rr, b Skip if bit in register is set if (Rr(b)=1) PC ← PC + 2 or 3 None 1/2/3
SBIC P, b Skip if bit in I/O register cleared if (P(b)=0) PC ← PC + 2 or 3 None 1/2/3
SBIS P, b Skip if bit in I/O register is set if (P(b)=1) PC ← PC + 2 or 3 None 1/2/3
BRBS s, k Branch if status flag set if (SREG(s) = 1) then PC ← PC +
k + 1 None 1/2
BRBC s, k Branch if status flag cleared if (SREG(s) = 0) then PC ← PC +
k + 1 None 1/2
BREQ k Branch if equal if (Z = 1) then PC ← PC + k + 1 None 1/2
BRNE k Branch if not equal if (Z = 0) then PC ← PC + k + 1 None 1/2
BRCS k Branch if carry set if (C = 1) then PC ← PC + k + 1 None 1/2
BRCC k Branch if carry cleared if (C = 0) then PC ← PC + k + 1 None 1/2
BRSH k Branch if same or higher if (C = 0) then PC ← PC + k + 1 None 1/2
BRLO k Branch if lower if (C = 1) then PC ← PC + k + 1 None 1/2
BRMI k Branch if minus if (N = 1) then PC ← PC + k + 1 None 1/2
BRPL k Branch if plus if (N = 0) then PC ← PC + k + 1 None 1/2
BRGE k Branch if greater or equal, signed if (N ⊕ V= 0) then PC ← PC + k + 1 None 1/2
BRLT k Branch if less than zero, signed if (N ⊕ V= 1) then PC ← PC + k + 1 None 1/2
BRHS k Branch if half carry flag set if (H = 1) then PC ← PC + k + 1 None 1/2
BRHC k Branch if half carry flag cleared if (H = 0) then PC ← PC + k + 1 None 1/2
BRTS k Branch if T flag set if (T = 1) then PC ← PC + k + 1 None 1/2
BRTC k Branch if T flag cleared if (T = 0) then PC ← PC + k + 1 None 1/2
BRVS k Branch if overflow flag is set if (V = 1) then PC ← PC + k + 1 None 1/2
BRVC k Branch if overflow flag is cleared if (V = 0) then PC ← PC + k + 1 None 1/2
BRIE k Branch if interrupt enabled if (I = 1) then PC ← PC + k + 1 None 1/2
BRID k Branch if interrupt disabled if (I = 0) then PC ← PC + k + 1 None 1/2
Bit and Bit- Test Instructions
SBI P, b Set bit in I/O register I/O (P, b) ← 1 None 2
CBI P, b Clear bit in I/O register I/O (P, b) ← 0 None 2
LSL Rd Logical shift left Rd(n+1) ← Rd (n), Rd(0) ← 0 Z,C,N,V 1
LSR Rd Logical shift right Rd (n) ← Rd(n+1), Rd(7) ← 0 Z,C,N,V 1
ROL Rd Rotate left through carry Rd(0) ← C, Rd(n+1) ← Rd (n),
C ← Rd(7) Z,C,N,V 1
ROR Rd Rotate right through carry Rd(7) ← C, Rd(n) ← Rd(n+1),
C ← Rd(0) Z,C,N,V 1
ASR Rd Arithmetic shift right Rd(n) ← Rd(n+1), n=0..6 Z,C,N,V 1
SWAP Rd Swap nibbles Rd(3..0) ← Rd(7..4), Rd(7..4) ←
Rd(3..0) None 1
BSET sFlag set SREG(s) ← 1 SREG(s) 1
BCLR sFlag clear SREG(s) ← 0 SREG(s) 1
BST Rr, b Bit store from register to T T ← Rr(b) T 1
6.5 Instruction Set Summary (Continued)
Mnemonics Operands Description Operation Flags #Clocks
Note: 1. These instructions are only available in ATA6613C
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
300
BLD Rd, b Bit load from T to register Rd(b) ← T None 1
SEC Set carry C ← 1 C 1
CLC Clear carry C ← 0 C 1
SEN Set negative flag N ← 1 N 1
CLN Clear negative flag N ← 0 N 1
SEZ Set zero flag Z ← 1 Z 1
CLZ Clear zero flag Z ← 0 Z 1
SEI Global interrupt enable I ← 1 I 1
CLI Global interrupt disable I ← 0 I 1
SES Set signed test flag S ← 1 S 1
CLS Clear signed test flag S ← 0 S 1
SEV Set twos complement overflow. V ← 1 V 1
CLV Clear twos complement overflow V ← 0 V 1
SET Set T in SREG T ← 1 T 1
CLT Clear T in SREG T ← 0 T 1
SEH Set half carry flag in SREG H ← 1 H 1
CLH Clear half carry flag in SREG H ← 0 H 1
Data Transfer Instructions
MOV Rd, Rr Move between registers Rd ← Rr None 1
MOVW Rd, Rr Copy register word Rd+1:Rd ← Rr+1:Rr None 1
LDI Rd, K Load immediate Rd ← K None 1
LD Rd, X Load indirect Rd ← (X) None 2
LD Rd, X+ Load indirect and post-inc. Rd ← (X), X ← X + 1 None 2
LD Rd, - X Load indirect and pre-dec. X ← X – 1, Rd ← (X) None 2
LD Rd, Y Load indirect Rd ← (Y) None 2
LD Rd, Y+ Load indirect and post-inc. Rd ← (Y), Y ← Y + 1 None 2
LD Rd, - Y Load indirect and pre-dec. Y ← Y – 1, Rd ← (Y) None 2
LDD Rd, Y+ q Load indirect with displacement Rd ← (Y + q) None 2
LD Rd, Z Load indirect Rd ← (Z) None 2
LD Rd, Z+ Load indirect and post-inc. Rd ← (Z), Z ← Z+1 None 2
LD Rd, -Z Load indirect and pre-dec. Z ← Z – 1, Rd ← (Z) None 2
LDD Rd, Z+q Load indirect with displacement Rd ← (Z + q) None 2
LDS Rd, k Load direct from SRAM Rd ← (k) None 2
ST X, Rr Store indirect (X) ← Rr None 2
ST X+, Rr Store indirect and post-inc. (X) ← Rr, X ← X + 1 None 2
ST – X, Rr Store indirect and pre-dec. X ← X – 1, (X) ← Rr None 2
ST Y, R r Store indirect (Y) ← Rr None 2
ST Y+, Rr Store indirect and post-inc. (Y) ← Rr, Y ← Y + 1 None 2
ST – Y, Rr Store indirect and pre-dec. Y ← Y – 1, (Y) ← Rr None 2
STD Y+q,Rr Store indirect with displacement (Y + q) ← Rr None 2
ST Z, Rr Store indirect (Z) ← Rr None 2
6.5 Instruction Set Summary (Continued)
Mnemonics Operands Description Operation Flags #Clocks
Note: 1. These instructions are only available in ATA6613C
301
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
ST Z+, Rr Store indirect and post-inc. (Z) ← Rr, Z ← Z + 1 None 2
ST –Z, Rr Store indirect and pre-dec. Z ← Z – 1, (Z) ← Rr None 2
STD Z+q,Rr Store indirect with displacement (Z + q) ← Rr None 2
STS k, Rr Store direct to SRAM (k) ← Rr None 2
LPM Load program memory R0 ← (Z) None 3
LPM Rd, Z Load program memory Rd ← (Z) None 3
LPM Rd, Z+ Load program memory and post-inc Rd ← (Z), Z ← Z+1 None 3
SPM Store program memory (Z) ← R1:R0 None –
IN Rd, P In port Rd ← P None 1
OUT P, R r Out port P ← Rr None 1
PUSH Rr Push register on stack STACK ← Rr None 2
POP Rd Pop register from stack Rd ← STACK None 2
MCU Control Instructions
NOP No operation None 1
SLEEP Sleep (see specific descr. for sleep function) None 1
WDR Watchdog reset (see specific descr. for WDR/timer) None 1
BREAK Break For on-chip debug only None N/A
6.5 Instruction Set Summary (Continued)
Mnemonics Operands Description Operation Flags #Clocks
Note: 1. These instructions are only available in ATA6613C
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
302
7. Application
Figure 7-1. Typical LIN Slave Application
Note: All open pins of the SiP can be used for application-specific purposes.
AVR: Internal clock, no ADC application, TXD, RXD, NRES, EN and NTRIG connected for LIN Slave. The
connection between the LIN-SBC and the AVR® requires the software being programmed correspondingly.
SBC: LIN slave operation with watchdog, 5V regulator and KL15 wake up
RF emissions: Best results for RF emissions will be achieved by connecting the blocking capacitors of the
microcontroller supply (C1 and C2) between the microcontroller pins and the GND/PVCC line.
See also Figure 7-1.
+
ATA6612C/ATA6613C
GND
KL_15
VBAT
LIN
ISP
PB3
PVCC
PB5
PC6
PB4
22μF100nF
10μF100nF 100nF
100nF
220pF
INH
PVCC
GND
WD_OSC
TM
MODE
KL_15
RXD
INH
TDX
NRES
PC6
PD0
PD1
PD2
48
47
46
45
40
39
38
37
44
43
42
41
13
14
15
16
21
22
23
24
17
18
19
20
PB7
PB6
MCUVCC
GND2
MCUVCC
GND1
PD4
LIN
PD3
WAKE
NTRIG
EN
VS
VCC
PVCC
10
9
12
11
6
5
8
7
2
1
4
3
27
28
25
26
31
32
29
30
35
36
33
34
PB5
PB0
PD7
PD6
PD5
PB4
PB3
PB2
PB1
MCUAVCC
ADC6
GND4
AREF
ADC7
PC0
PC1
PC2
PC3
PC4
PC5
1
+
10kΩ
47kΩ
51kΩ
C2
100nF
C1
100nF
Atmel
10kΩ*
MODE*
* The MODE pin can be connected directly to GND, if it is not needed to disable the Watchdog
PB5
PB3PB4
PC6
303
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
Figure 7-2. Typical LIN Master Application
Note: All open pins of the SiP can be used for application-specific purposes.
AVR: TXD, RXD, NRES and EN connected for LIN Master. The connection between the LIN-SBC and the AVR
requires the software being programmed correspondingly. Analog digital converter not active; system clock
from external crystal.
LIN-SBC: Master application with 5V regulator and watchdog, 1k master resistance connected via diode to
VBAT, local wake up via pin WAKE.
RF emissions: Best results for RF emissions will be achieved by connecting the blocking capacitors of the
microcontroller supply (C1 and C2) between the microcontroller pins and the GND/PVCC line.
See also Figure 7-2.
+
ATA6612C/ATA6613C
XTAL
GND
VBAT
LIN
ISP
WAKE
PB3
PVCC
PB5
PC6
PB4
22μF100nF
10μF100nF
100nF
560pF
22pF22pF
PVCC
GND
WD_OSC
TM
MODE
KL_15
RXD
INH
TDX
NRES
PC6
PD0
PD1
PD2
48
47
46
45
40
39
38
37
44
43
42
41
13
14
15
16
21
22
23
24
17
18
19
20
PB7
PB6
MCUVCC
GND2
MCUVCC
GND1
PD4
LIN
PD3
WAKE
NTRIG
EN
VS
VCC
PVCC
10
9
12
11
6
5
8
7
2
1
4
3
27
28
25
26
31
32
29
30
35
36
33
34
PB5
PB0
PD7
PD6
PD5
PB4
PB3
PB2
PB1
MCUAVCC
ADC6
GND4
AREF
ADC7
PC0
PC1
PC2
PC3
PC4
PC5
33kΩ
10kΩ
1kΩ
1
+
C2
100nF
C1
100nF
10kΩ
Atmel
51kΩ
* The MODE pin can be connected directly to GND, if it is not needed to disable the Watchdog
10kΩ*
MODE*
PB3PB4
PB5
PC6
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
304
Figure 7-3. Typical LIN Master Application
LIN Master Pull-up Switched Off during Sleep Mode
Note: All open pins of the SiP can be used for application-specific purposes.
AVR: TXD, RXD, NRES and EN connected for LIN Master. The connection between the LIN-SBC and the AVR
requires the software being programmed correspondingly. Analog digital converter not active; system clock
from external crystal.
LIN-SBC: Master application with 5V regulator and watchdog, 1k master resistance connected via diode and
INH output to VBAT, local wake up via pin WAKE.
RF emissions: Best results for RF emissions will be achieved by connecting the blocking capacitors of the
microcontroller supply (C1 and C2) between the microcontroller pins and the GND/PVCC line.
See also Figure 7-3.
+
ATA6612C/ATA6613C
XTAL
GND
VBAT
LIN
ISP
WAKE
PB3
PVCC
PB5
PC6
PB4
22μF100nF
10μF100nF
100nF
560pF
22pF22pF
PVCC
GND
WD_OSC
TM
MODE
KL_15
RXD
INH
TDX
NRES
PC6
PD0
PD1
PD2
48
47
46
45
40
39
38
37
44
43
42
41
13
14
15
16
21
22
23
24
17
18
19
20
PB7
PB6
MCUVCC
GND2
MCUVCC
GND1
PD4
LIN
PD3
WAKE
NTRIG
EN
VS
VCC
PVCC
10
9
12
11
6
5
8
7
2
1
4
3
27
28
25
26
31
32
29
30
35
36
33
34
PB5
PB0
PD7
PD6
PD5
PB4
PB3
PB2
PB1
MCUAVCC
ADC6
GND4
AREF
ADC7
PC0
PC1
PC2
PC3
PC4
PC5
33kΩ
10kΩ
1kΩ
1
+
C2
100nF
C1
100nF
10kΩ
10kΩ
Atmel
51kΩ
* The MODE pin can be connected directly to GND, if it is not needed to disable the Watchdog
10kΩ*
MODE*
PC6
PB5
PB3PB4
305
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
Figure 7-4. LIN Slave Application with Minimum External Components
Note: All open pins of the SiP can be used for application-specific purposes.
AVR: Internal clock, no ADC application, TXD, RXD, NRES and EN connected for LIN Slave. The connection
between the LIN-SBC and the AVR requires the software being programmed correspondingly.
SBC: LIN slave operation with 5V regulator, no watchdog, no local wake-up.
RF emissions: Best results for RF emissions will be achieved by connecting the blocking capacitors of the
microcontroller supply (C1 and C2) between the microcontroller pins and the GND/PVCC line.
See also Figure 7-4.
+
ATA6612C/ATA6613C
GND
VBAT
LIN
ISP
PB3
PVCC
PB5
PC6
PB4
22μF100nF
10μF100nF
100nF
220pF
PVCC
GND
WD_OSC
TM
MODE
KL_15
RXD
INH
TDX
NRES
PC6
PD0
PD1
PD2
48
47
46
45
40
39
38
37
44
43
42
41
13
14
15
16
21
22
23
24
17
18
19
20
PB7
PB6
MCUVCC
GND2
MCUVCC
GND1
PD4
LIN
PD3
WAKE
NTRIG
EN
VS
VCC
PVCC
10
9
12
11
6
5
8
7
2
1
4
3
27
28
25
26
31
32
29
30
35
36
33
34
PB5
PB0
PD7
PD6
PD5
PB4
PB3
PB2
PB1
MCUAVCC
ADC6
GND4
AREF
ADC7
PC0
PC1
PC2
PC3
PC4
PC5
1
+
10kΩ
C1
100nF
C2
100nF
Atmel
PB5
PB3PB4
PC6
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
306
9. Package Information
8. Ordering Information
Extended Type Number Program Memory Package MOQ
ATA6612C-PLQW-1 8kB flash QFN48, 7×74,000 pieces
ATA6613C-PLQW-1 16kB flash QFN48, 7×74,000 pieces
Package Drawing Contact:
packagedrawings@atmel.com
GPC DRAWING NO.
REV. TITLE
6.543-5188.03-4 1
05/20/14
Package: QFN_7x7_48L
Exposed pad 5.6x5.6
COMMON DIMENSIONS
(Unit of Measure = mm)
MIN NOM NOTEMAXSymbol
Dimensions in mm
specifications
according to DIN
technical drawings
0.035 0.050A1
77.16.9E
0.25 0.30.2b
0.5e
0.4 0.450.35L
5.6 5.75.5E2
5.6 5.75.5D2
77.16.9D
0.21 0.260.16A3
0.85 0.90.8A
b
L
A (10:1)
A
D
1
12
48
PIN 1 ID
E
Top View
A
A3
A1
E2
Side View
Bottom View
e
D2
48 37
13
12
1
24
25
36
307
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
10. Errata
10.1 Atmel ATA6612C
●Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous timer
If one of the timer registers which is synchronized to the asynchronous timer2 clock is written in the cycle before an overflow
interrupt occurs, the interrupt may be lost.
Problem Fix/Workaround
Always check that the timer2 timer/counter register, TCNT2, does not have the value 0xFF before writing the timer2 control
register, TCCR2, or output compare register, OCR2.
10.2 Atmel ATA6613C
●Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous timer
If one of the timer registers which is synchronized to the asynchronous timer2 clock is written in the cycle before an overflow
interrupt occurs, the interrupt may be lost.
Problem Fix/Workaround
Always check that the timer2 timer/counter register, TCNT2, does not have the value 0xFF before writing the timer2 control
register, TCCR2, or output compare register, OCR2.
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
308
11. Revision History
Please note that the following page numbers referred to in this section refer to the specific revision mentioned, not to this
document.
Revision No. History
9111L-AUTO-11/14
• Put datasheet in the latest template
• Section 8 “Ordering Information” on page 306 updated
• Section 9 “Package Information” on page 306 updated
9111K-AUTO-03/13
• Section 2 “Pin Configuration” on pages 2 to 3 updated
• Table 3-1 “Maximum Ratings of the SIP” on page 4 updated
• Table 3-2 “Maximum Ratings of the LIN-SBC” on pages 4 to 5 added
• Table 3-3 “Maximum Ratings of the Microcontroller” on page 5 added
• Figure 8-1 “Typical LIN Slave Application” on page 351 updated
• Figure 8-2 “Typical LIN Master Application” on page 352 updated
• Figure 8-3 “LIN Slave Application with Minimum External Components” on page 353
updated
• Figure 8-4 “Typical LIN Master Application LIN Master Pull-up Switched Off during Sleep
Mode” on page 354 updated
9111J-AUTO-11/12 • ATA6612P/ATA6613P renamed in ATA6612C/ATA6613C
9111I-AUTO-02/12
• General Features on page 1 changed
• Section 3.1 “Features” on page 5 changed
• Section 3.3 “Functional Description” on pages 7 to 19 changed
• Section 4 “Absolute Maximum Ratings” on page 20 changed
• Section 5 “Electrical Characteristics” on page 21 changed
• Section 8 “Application” on pages 355 to 358 changed
9111H-AUTO-01/11
• Section 3.1 “Features” on page 5 changed
• Section 3.3.3 “Ground Pin” on page 7 changed
• Section 3.3.12 “Mode Input Pin (Mode)” on page 8 changed
• Figure 3.2 “Modes of Operation” on page 10 changed
• Section 3.3.20.4 “Fail-safe Mode” on page 13 changed
• Section 3.3.23 “Voltage Regulator” on pages 16 to 17 changed
• Section 6 “Electrical Characteristics” on pages 21 to 26 changed
9111G-AUTO-05/10
• Table 2-2 “Maximum Ratings of the SiP” on page 4 changed
• Section 3.1 “Features” on page 5 changed
• Section 3.2 “Description” on page 5 changed
• Section 3.3.1 “Physical Layer Compatibility” on page 7 changed
• Section 3.3.6 “Bus Pin LIN” on page 7 changed
• Section 3.3.8 “TX Dominant Time-out Function” on page 8 changed
• Section 3.3.10 “Enable Input Pin (EN)” on page 8 changed
• Section 3.3.14 “KL_15 Pin” on page 9 changed
• Section 3.3.20 “Modes of Operation” on pages 10 to 14 changed
• Section 3.3.21 “Wake-up Scenarios from Silent to Sleep Mode on page 15 changed
• Section 3.3.23 “Voltage Regulator” on page 16 changed
• Section 6 “Electrical Characteristics” on page 23 changed
• Section 7.7.7.1 “Power Reduction Register” on page 66 changed
309
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
9111F-AUTO-12/08 • Section 11 “Errata” on page 360 changed
9111E-AUTO-07/08
• Table 2-2 “Maximum Ratings of the SiP” on page 4 changed
• Section 4 “Absolute Maximum Ratings” on page 20 changed
• Figure 8-1 “Typical LIN Slave Application” on page 355 changed
• Figure 8-2 “Typical LIN Master Application” on page 356 changed
• Figure 8-3 “LIN Slave Application with Minimum External Components” on page 357
changed
• Figure 8-4 “Typical LIN Master Application LIN Master Pull-up Switched Off during Sleep
Mode” on page 358 added
9111D-AUTO-06/08
• Figure 3-1 “Block Diagram” on page 6 changed
• Section 3.3 “Functional Description” on pages 7 to 18 changed
• Section 6.5.3.2 “The EEPROM Address Register – EEARH and EEARL” on page 45
changed
9111C-AUTO-02/08 • Figure 8-2 “Typical LIN Master Application” on page 356 changed
9111B-AUTO-11/07
• Section 5 “Electrical Characteristics” on pages 21 to 26 changed
• Section 6.6.6 “Calibrated Internal RC Oscillator” on page 57 changed
• Figure 8-3 “LIN Slave Application with Minimum External Components on page 357 added
Please note that the following page numbers referred to in this section refer to the specific revision mentioned, not to this
document.
Revision No. History
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
310
12. Table of Contents
General Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1. Pin Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Absolute Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. LIN System-basis-chip Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5. Microcontroller Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.1 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.3 About Code Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.4 AVR CPU Core . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.5 AVR Atmel ATA6612C/ATA6613C Memories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
5.6 System Clock and Clock Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
5.7 Power Management and Sleep Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.8 System Control and Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.9 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5.10 I/O-Ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.11 External Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
5.12 8-bit Timer/Counter0 with PWM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
5.13 Timer/Counter0 and Timer/Counter1 Prescalers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
5.14 16-bit Timer/Counter1 with PWM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
5.15 8-bit Timer/Counter2 with PWM and Asynchronous Operation . . . . . . . . . . . . . . . . . . . . . . 137
5.16 Serial Peripheral Interface – SPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
5.17 USART0. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
5.18 USART in SPI Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
5.19 2-wire Serial Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
5.20 Analog Comparator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
5.21 Analog-to-Digital Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
5.22 debugWIRE On-chip Debug System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
5.23 Boot Loader Support – Read-While-Write Self-Programming,
Atmel ATA6612C and ATA6613C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
5.24 Memory Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
5.25 Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
5.26 LIN Re-synchronization Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
6. 2-wire Serial Interface Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
6.1 SPI Timing Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
6.2 ADC Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
6.3 Atmel ATA6612C/ATA6613C Typical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
6.4 Register Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
6.5 Instruction Set Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
7. Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
8. Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
311
ATA6612C/ATA6613C [DATASHEET]
9111L–AUTO–11/14
9. Package Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
10. Errata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307
10.1 Atmel ATA6612C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307
10.2 Atmel ATA6613C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307
11. Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
12. Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
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