9140E-INDCO-09/14
General Features
●Transmitter with microcontroller consisting of an AVR® microcontroller and RF
transmitter PLL in a single QFN24 5mm × 5mm package (pitch 0.65mm)
●f0 = 310MHz to 350MHz
●Temperature range –40°C to +85°C
●Supply voltage 2.0V to 4.0V allowing usage of single li-cell power supply
●Low power consumption
●Active mode: typical 9.8mA at 3.0V and 4MHz microcontroller-clock
●Power-down mode: typical 200nA at 3.0V
●Modulation scheme ASK/FSK
●Integrated PLL loop filter
●Output power of 8dBm at 315MHz
●Easy to design-in due to excellent isolation of the PLL from the PA and power
supply
●Single-ended antenna output with high efficient power amplifier
●Very robust ESD protection: HBM 2500V, MM100V, CDM 1000V
●High performance, low power AVR 8-bit microcontroller, similar to popular Atmel
ATtiny44
●Well known and market-accepted RISC architecture
●Non-volatile program and data memories
●4Kbytes of in-system programmable program memory flash
●256Bytes in-system programmable EEPROM
●256Bytes internal SRAM
●Programming lock for self-programming flash program and EEPROM data security
●Peripheral features
●Two timer/counter, 8- and 16-bit counters with two PWM channels on both
●10-bit ADC
●On-chip analog comparator
●Programmable watchdog timer with separate on-chip oscillator
●Universal serial interface (USI)
ATA8741
Microcontroller with UHF ASK/FSK Transmitter
DATASHEET
ATA8741 [DATASHEET]
9140E–INDCO–09/14
2
●Special microcontroller features
●debugWIRE on-chip debug system
●In-system programmable via SPI port
●External and internal interrupt sources
●Pin change interrupt on 12 pins
●Enhanced power-on reset circuit
●Programmable brown-out detection circuit
●Internal calibrated oscillator
●On-chip temperature sensor
●12 programmable I/O lines
3
ATA8741 [DATASHEET]
9140E–INDCO–09/14
1. General Description
The Atmel® ATA8741 is a highly flexible programmable transmitter containing the AVR® microcontroller Atmel ATtiny44V
and the UHF PLL transmitters in a small QFN24 5mm ×5mm package. This device is a member of a transmitter family
covering several operating frequency ranges, which has been specifically developed for the demands of RF low-cost data
transmission systems with data rates of up to 32kBit/s. Its primary applications are in the areas of industrial/aftermarket
remote keyless-entry (RKE) systems, alarm, telemetering, energy metering systems, home automotion/entertainment and
toys. The Atmel ATA8741 can be used in the frequency band of f0= 315MHz for ASK or FSK data transmission.
Figure 1-1. ASK System Block Diagram
UHF ASK/FSK
Remote Control Receiver
UHF ASK/FSK
Remote Control Transmitter
ATA8741
Antenna
Loop
Antenna
VS
VS
1 to 6
Micro-
controller
Demod
VCC_RF
GND_RF
PA_ENABLE
ATtiny44V
ATA8401
ATA8404
ATA8201
ATA8203
ENABLE
Control
XTOPLL
VCOLNA
XTO
PA
VCO
f/4 PLL
Power
up/down
ANT1
ANT2
PXY
S1
S1
S1
PXY
PXY
PXY
PXY
PXY
PXY
VDD
GND
PXY
PXY
PXY
PXY
PXY
VS
CLK
ATA8741 [DATASHEET]
9140E–INDCO–09/14
4
Figure 1-2. FSK System Block Diagram
UHF ASK/FSK
Remote Control Receiver
UHF ASK/FSK
Remote Control Transmitter
ATA8741
Antenna
Loop
Antenna
VS
VS
1 to 6 Micro-
controller
Demod
VCC_RF
GND_RF
PA_ENABLE
ATtiny44V
ATA8401
ATA8404
ATA8201
ATA8203
ENABLE
Control
XTOPLL
VCOLNA
XTO
PA
VCO
f/4 PLL
Power
up/down
ANT1
ANT2
PXY
S1
S1
S1
PXY
PXY
PXY
PXY
PXY
PXY
VDD
GND
PXY
PXY
PXY
PXY
PXY
CLK
VS
5
ATA8741 [DATASHEET]
9140E–INDCO–09/14
2. Pin Configuration
Figure 2-1. Pinning QFN24 5mm x 5mm
Table 2-1. Pin Description
Pin Symbol Function
1VCC Microcontroller supply voltage
2PB0 Port B is a 4-bit bi-directional I/O port with internal pull-up resistor
3PB1 Port B is a 4-bit bi-directional I/O port with internal pull-up resistor
4PB3/RESET Port B is a 4-bit bi-directional I/O port with internal pull-up resistor/reset input
5PB2 Port B is a 4-bit bi-directional I/O port with internal pull-up resistor
6PA7 Port A is a 4-bit bi-directional I/O port with internal pull-up resistor
7PA6 / MOSI Port A is a 4-bit bi-directional I/O port with internal pull-up resistor
8CLK Clock output signal for microcontroller. The clock output frequency is set by the crystal to
fXTAL/4
9PA_ENABLE Switches on power amplifier. Used for ASK modulation
10 ANT2 Emitter of antenna output stage
11 ANT1 Open collector antenna output
12 GND Ground
13 PA5/MISO Port A is a 4-bit bi-directional I/O port with internal pull-up resistor
14 PA4/SCK Port A is a 4-bit bi-directional I/O port with internal pull-up resistor
15 PA3/T0 Port A is a 4-bit bi-directional I/O port with internal pull-up resistor
16 PA2 Port A is a 4-bit bi-directional I/O port with internal pull-up resistor
17 PA1 Port A is a 4-bit bi-directional I/O port with internal pull-up resistor
18 PA0 Port A is a 4-bit bi-directional I/O port with internal pull-up resistor
19 GND Microcontroller ground
20 XTAL Connection for crystal
21 VS_RF Transmitter supply voltage
22 GND_RF Transmitter ground
23 ENABLE Enable input
24 GND Ground
GND Ground/backplane (exposed die pad)
PB3/RESET
PB2
PA7
PB1
PB0
VCC
PA3/T0
PA4/USCK
PA5/MISO
PA2
PA1
PA0
VS_RF
XTAL
GND
GND_RF
ENABLE
GND
ANT2
ANT1
GND
PA_ENABLE
CLK
PA6/MOSI
24
4
3
6
5
2
1
15
16
13
14
17
18
23 22 21 20 19
789101112
ATA8741 [DATASHEET]
9140E–INDCO–09/14
6
2.1 Pin Configuration of RF Pins
Table 2-2. Pin Description
Pin Symbol Function Configuration
8CLK
Clock output signal for
microcontroller.
The clock output frequency is set by
the crystal to fXTAL/4.
9PA_ENABLE Switches on power amplifier.
Used for ASK modulation.
10
11
ANT2
ANT1
Emitter of antenna output stage.
Open collector antenna output.
20 XTAL Connection for crystal.
100Ω
100Ω
CLK
VS
50kΩ
20μA
UREF = 1.1VPA_ENABLE
ANT1
ANT2
1.5kΩ 1.2kΩ
182μA
XTAL
VS VS
7
ATA8741 [DATASHEET]
9140E–INDCO–09/14
21 VS Supply voltage See ESD protection circuitry (see Figure 8-1 on page 12).
22 GND Ground See ESD protection circuitry (see Figure 8-1 on page 12).
23 ENABLE Enable input
Table 2-2. Pin Description (Continued)
Pin Symbol Function Configuration
200kΩENABLE
ATA8741 [DATASHEET]
9140E–INDCO–09/14
8
3. Functional Description
For a typical application 3 to 4 interconnections between the AVR® and the transmitter are required
(see Figure 1-1 on page 3 and Figure 1-2 on page 4). The CLK line is used to allow the microcontroller to generate an XTAL-
based transmitter signal. The ENABLE line is used to start the transmitter’s XTO, PLL, and clock. The PA_ENABLE line is
used to enable the power amplifier in ASK and FSK mode. In FSK mode a fourth line is necessary to modulate the load
capacity of the XTAL. To wake up the system from standby mode at least one key input is required. After pressing the key,
the microcontroller starts up with the internal RC oscillator. For TX operation user software must control ENABLE,
PA_ENABLE, and XTAL load capacity as described in the following section.
If ENABLE = L and PA_ENABLE = L the transmitter and the microcontroller (MCU) are in standby mode, reducing the power
consumption so that a lithium cell can be used as power supply for several years.
If ENABLE = H and PA_ENABLE = L, the XTO, PLL, and the CLK driver from the transmitter are activated. The crystal
oscillator together with the PLL from the RF transmitter typically require < 3ms until the PLL is locked and the clock output
(Pin 8) is stable.
If ENABLE = H and PA_ENABLE = H, the XTO, PLL, CLK driver, and the power amplifier (PA) are switched on. ASK
modulation is achieved by switching on and off the power amplifier via PA_ENABLE. FSK modulation is achieved by
switching on and off an additional capacitor between the XTAL load capacitor and GND, thus changing the reference
frequency of the PLL. This is done using a MOS switch controlled by a microcontroller output. The power amplifier is
switched on via PA_ENABLE = H.
The MCU has to wait at least > 3ms after setting ENABLE = H, before the external clock can be used. The external clock is
connected via the timer0 input pin that clocks the USI from the MCU to achieve an accurate data transfer. The frequency of
the internal RC oscillator is affected by ambient temperature and operating voltage.
The USI provides two serial synchronous data transfer modes, with different physical I/O ports for the data output. The two
wire mode is used for ASK and the three wire mode is used for FSK.
If ENABLE = L and the PA_ENABLE = L, the circuit is in standby mode consuming only a very small amount of current so
that a lithium cell used as power supply can work for several years.
With ENABLE = H the XTO, PLL, and the CLK driver are switched on. If PA_ENABLE remains L only the PLL and the XTO
are running and the CLK signal is delivered to the microcontroller. The VCO locks to 32 times the XTO frequency.
With ENABLE = H and PA_ENABLE = H the PLL, XTO, CLK driver, and the power amplifier are on. With PA_ENABLE the
power amplifier can be switched on and off, which is used to perform the ASK modulation.
3.1 Description of RF Transmitter
The integrated PLL transmitter is particularly suitable for simple, low-cost RF applications. The VCO is locked to 32 fXTAL
hence a 9.8438MHz crystal is needed for a 315MHz transmitter. All other PLL and VCO peripheral elements are integrated.
The XTO is a series resonance oscillator so that only one capacitor together with a crystal connected in series to GND are
needed as external elements.
The crystal oscillator together with the PLL typically need < 3ms until the PLL is locked and the CLK output is stable. There
is a wait time of ≥3ms until the CLK is used for the microcontroller and the PA is switched on.
The power amplifier is an open-collector output delivering a current pulse, which is nearly independent from the load
impedance. Thus, the delivered output power is controllable via the connected load impedance.
This output configuration enables simple matching to any kind of antenna or to 50Ω. This results in a high power efficiency of
η=P
out/(IS,PA V
S) of 40% for the power amplifier when an optimized load impedance of ZLoad =(255+j192)Ω is used at 3V
supply voltage.
3.2 ASK Transmission
The RF TX block is activated by ENABLE = H. PA_ENABLE must remain L for typically ≥3ms, then the CLK signal is taken
to clock the AVR and the output power can be modulated by means of pin PA_ENABLE. After transmission, PA_ENABLE is
switched to L and the microcontroller switches back to internal clocking. The RF TX is switched back to standby mode with
ENABLE = L.
9
ATA8741 [DATASHEET]
9140E–INDCO–09/14
3.3 FSK Transmission
The RF TX is activated by ENABLE = H. PA_ENABLE must remain L for typically ≥3ms, then the CLK signal is taken to
clock the AVR® and the power amplifier is switched on with PA_ENABLE = H. The chip is then ready for FSK modulation.
The AVR starts to switch on and off the capacitor between the XTAL load capacitor and GND with an open-drain output port,
thus changing the reference frequency of the PLL. When the switch is closed, the output frequency is lower than when the
switch is open. After transmission, PA_ENABLE is switched to L and the microcontroller switches back to internal clocking.
The RF TX is switched back to standby mode with ENABLE = L.
The accuracy of the frequency deviation with XTAL pulling method is about ±25% when the following tolerances are
considered.
Figure 3-1. Tolerances of Frequency Modulation
Using C4= 8.2pF ±5%, C5= 10pF ±5%, a switch port with CSwitch = 3pF ±10%, stray capacitances on each side of the crystal
of CStray1 =C
Stray2 = 1pF ±10%, a parallel capacitance of the crystal of C0= 3.2pF ±10% and a crystal with CM= 13fF ±10%,
results in a typical FSK deviation of ±21.5kHz with worst case tolerances of ±16.25kHz to ±28.01kHz.
3.4 CLK Output
An output CLK signal is provided for the integrated AVR. The delivered signal is CMOS compatible if the load capacitance is
lower than 10pF.
3.4.1 Clock Pulse Take-over
The clock of the crystal oscillator can be used for clocking the microcontroller. Atmel®’s AVR microcontroller starts with an
integrated RC-oscillator to switch on the RF TX with ENABLE = H, and after 3ms assumes the clock signal of the
transmission IC, so that the message can be sent with crystal accuracy.
3.4.2 Output Matching and Power Setting
The output power is set by the load impedance of the antenna. The maximum output power is achieved with a load
impedance of ZLoad,opt =(255+j192)Ω. There must be a low resistive path to VS to deliver the DC current.
The delivered current pulse of the power amplifier is 9mA and the maximum output power is delivered to a resistive load of
400Ω if the 1.0pF output capacitance of the power amplifier is compensated by the load impedance.
An optimum load impedance of:
ZLoad = 400Ω|| j/(2 ×π1.0pF) = (255 + j192)Ω is achieved for the maximum output power of 8dBm.
The load impedance is defined as the impedance seen from the RF TX’s ANT1, ANT2 into the matching network. This large
signal load impedance should not be confused with the small signal input impedance delivered as input characteristic of RF
amplifiers and measured from the application into the IC instead of from the IC into the application for a power amplifier.
Less output power is achieved by lowering the real parallel part of 400Ω where the parallel imaginary part should be kept
constant.
Output power measurement can be done using the circuit shown in Figure 8-4 on page 15. Note that the component values
must be changed to compensate for the individual board parasitics until the RF TX has the right load impedance
ZLoad,opt =(255+j192)Ω. In addition, the damping of the cable used to measure the output power must be calibrated out.
RS
LMC4
CM
VS
XTAL
Crystal equivalent circuit
C0C5
CSwitch
CStray1 CStray2
ATA8741 [DATASHEET]
9140E–INDCO–09/14
10
4. Microcontroller Block
More detailed information about the microcontroller block can be found in the appendix.
5. Absolute Maximum Ratings
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 Minimum Maximum Unit
Supply voltage VS5 V
Power dissipation Ptot 100 mW
Junction temperature Tj150 °C
Storage temperature Tstg –55 125 °C
Ambient temperature Tamb –55 125 °C
Input voltage VmaxPA_ENABLE –0.3 (VS + 0.3)(1) V
Notes: 1. If VS + 0.3 is higher than 3.7V, the maximum voltage will be reduced to 3.7V.
6. Thermal Resistance
Parameters Symbol Value Unit
Junction ambient RthJA 35 K/W
7. Electrical Characteristics
VS = 2.0V to 4.0V, Tamb = 25°C unless otherwise specified.
Typical values are given at VS= 3.0V and Tamb = 25°C. All parameters are referred to GND (pin 7).
Parameters Test Conditions Symbol Min. Typ. Max. Unit
Supply current Power down, microcontroller Watchdog
timer disabled IS_Off
210
24.35
nA
µA
Supply current Power up, 4MHz internal RC oscillator IS_Transmit 9.8 mA
Output power VS=3.0V, T
amb = 25°C,
f = 315MHz, ZLoad = (255 + j192)ΩPRef 6.0 8.0 10.5 dBm
Output power variation for the full
temperature range
Tamb = 25°C,
VS = 3.0V
VS = 2.0V
ΔPRef
ΔPRef
–1.5
–4.0
dB
dB
Output power variation for the full
temperature range
Tamb = 25°C,
VS = 3.0V
VS = 2.0V,
POut = PRef + ΔPRef
ΔPRef
ΔPRef
–2.0
–4.5
dB
dB
Achievable output-power range Selectable by load impedance POut_typ 08.0 dBm
Spurious emission
fCLK = f0/128
Load capacitance at pin CLK = 10pF
fO ±1 ×fCLK
fO ±4 ×fCLK
other spurious are lower
–55
–52
dBc
dBc
Notes: 1. If VS is higher than 3.6V, the maximum voltage will be reduced to 3.6V.
11
ATA8741 [DATASHEET]
9140E–INDCO–09/14
Oscillator frequency XTO
(= phase comparator frequency)
fXTO = f0/32
fXTAL = resonant frequency of the XTAL,
CM ≤10fF, load capacitance selected
accordingly
Tamb = 25°C
fXTO
–30 fXTAL +30 ppm
PLL loop bandwidth 250 kHz
Phase noise of phase comparator Referred to fPC = fXT0,
25kHz distance to carrier –116 –110 dBc/Hz
In-loop phase noise PLL 25kHz distance to carrier –86 –80 dBc/Hz
Phase noise VCO at 1MHz
at 36MHz
–94
–125
–90
–121
dBc/Hz
dBc/Hz
Frequency range of VCO fVCO 310 350 MHz
Clock output frequency (CMOS
microcontroller compatible) f0/128 MHz
Voltage swing at pin CLK CLoad ≤10pF V0h
V0l
VS
× 0.8 VS
× 0.2 V
V
Series resonance R of the crystal Rs 110 Ω
Capacitive load at pin XT0 7pF
FSK modulation frequency rate Duty cycle of the modulation signal =
50% 032 kHz
ASK modulation frequency rate Duty cycle of the modulation signal =
50% 032 kHz
ENABLE input
Low level input voltage
High level input voltage
Input current high
VIl
VIh
IIn
1.7
0.25
20
V
V
µA
PA_ENABLE input
Low level input voltage
High level input voltage
Input current high
VIl
VIh
IIn
1.7
0.25
VS(1)
5
V
V
µA
7. Electrical Characteristics (Continued)
VS = 2.0V to 4.0V, Tamb = 25°C unless otherwise specified.
Typical values are given at VS= 3.0V and Tamb = 25°C. All parameters are referred to GND (pin 7).
Parameters Test Conditions Symbol Min. Typ. Max. Unit
Notes: 1. If VS is higher than 3.6V, the maximum voltage will be reduced to 3.6V.
ATA8741 [DATASHEET]
9140E–INDCO–09/14
12
8. Application
For the blocking of the supply voltage, a capacitor value of C3= 68nF/X7R is recommended. C1 and C2 are used to match
the loop antenna to the power amplifier, where C1 typically is 22pF/NP0 and C2 is 10.8pF/NP0 (18pF + 27pF in series); for
C2 two capacitors in series should be used to achieve a better tolerance value and to have the possibility of realizing the
ZLoad,opt using standard valued capacitors.
Together with the pins and the PCB board wires C1 forms a series resonance loop that suppresses the 1st harmonic, hence
the position of C1 on the PCB is important. Normally the best suppression is achieved when C1 is placed as close as possible
to the pins ANT1 and ANT2.
The loop antenna should not exceed a width of 1.5mm, otherwise the Q-factor of the loop antenna is too high.
L1 (50nH to 100nH) can be printed on PCB. C4 should be selected that the XTO runs on the load resonance frequency of the
crystal. Normally, a value of 12pF results for a 15pF load-capacitance crystal.
Figure 8-1. ESD Protection Circuit
Figure 8-2. Typical ASK Application ATA8741
CLK
VS
GND
PA_ENABLE XTALANT2 ENABLE
ANT1
PB0/XTAL1
VDD
PB3/RESET
PB2
PA7
ADC7
GND_RF
GND
XTAL
VCC_RF
ENABLE
GND
PA_ENABLE
GND
ANT1
ANT2
CLK
PA6
ADC6
PB1/XTAL2
PA1
PA0
13
14
15
16
17
18
6
5
4
3
2
1
20 1922 2124 23
11 1291078
PA3/T0
PA4/SCK
PA5/MISO
PA2
C5
VCC
VCC
VCC
L1
ATA874x
SW1
SW3
SW2
C8
Q1
C6
R3
C7
R2
R4
R1
C4
C3
C2
L2
C1
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ATA8741 [DATASHEET]
9140E–INDCO–09/14
Table 8-1. Bill of Material
Component Value
Type/
Manufacturer Note
315MHz 433.92MHz 868.3MHz
L1 100nH 82nH 22nH LL1608-FSL/
TOKO
L2 39nH 27nH 2.2nH LL1608-FSL/
TOKO
C1 1nF 1nF 1nF GRM1885C/
Murata
C2 3.9pF 2.7pF 1.5pF GRM1885C/
Murata
This cap must be placed as close as
possible to the pin Ant1 and Ant2
C3 27pF 16pF 4.3pF GRM1885C/
Murata
On the demo board 2 capacitors in
series are used to reduce the tolerance
C4 3.9pF 1.6pF 0.3pF GRM1885C/
Murata
On the demo board 2 capacitors in
series are used to reduce the tolerance
C5 68nF 68nF 68nF GRM188R71C/
Murata
This cap must placed as close as
possible to the VCC_RF
C6 100nF 100nF 100nF GRM188R71C /
Murata
This cap must placed as close as
possible to the VDD
C7 100nF 100nF 100nF GRM188R71C/
Murata
C8 10pF 12pF 12pF GRM1885C/
Murata
Q1 9.843750MHz 13.56MHz 13.567187
MHz
DSX530GK/
KDS
R1 100kΩ100kΩ100kΩ
R2 100kΩ100kΩ100kΩ
R3 10kΩ10kΩ10kΩ
R4 1.8kΩ1.8kΩ1.8kΩ
This resistor can be resigned if the ASK
modulation is performed using PA5
(MISO).
ATA8741 [DATASHEET]
9140E–INDCO–09/14
14
Figure 8-3. Typical FSK Application ATA8741
Note: FSK modulation is achieved by switching on and off an additional capacitor between the XTAL load capacitor
and GND. This is done using a MOS switch controlled by a microcontroller output.
Table 8-2. Bill of Material
Component Value
Type/
Manufacturer Note
315MHz 433.92MHz 868.3MHz
L1 100nH 82nH 22nH LL1608-FSL/
TOKO
L2 39nH 27nH 2.2nH LL1608-FSL/
TOKO
C1 1nF 1nF 1nF GRM1885C/
Murata
C2 3.9pF 2.7pF 1.5pF GRM1885C/
Murata
This cap must be placed as close as
possible to the pin Ant1 and Ant2
C3 27pF 16pF 4.3pF GRM1885C/
Murata
On the demo board 2 capacitors in series
are used to reduce the tolerance
C4 3.9pF 1.6pF 0.3pF GRM1885C/
Murata
On the demo board 2 capacitors in series
are used to reduce the tolerance
C5 68nF 68nF 68nF GRM188R71C/
Murata
This cap must placed as close as possible to
the VCC_RF
C6 100nF 100nF 100nF GRM188R71C /
Murata
This cap must placed as close as possible to
the VDD
C7 100nF 100nF 100nF GRM188R71C /
Murata
PB0/XTAL1
VDD
PB3/RESET
PB2
PA7
ADC7
GND_RF
GND
XTAL
VCC_RF
ENABLE
GND
PA_ENABLE
GND
ANT1
ANT2
CLK
PA6
ADC6
PB1/XTAL2
PA1
PA0
13
14
15
16
17
18
6
5
4
3
2
1
20 1922 2124 23
11 1291078
PA3/T0
PA4/SCK
PA5/MISO
PA2
C5
VCC
VCC
VCC
ATA874x
SW1
SW3
SW2
T1
C9
Q1
C8
C6
C7
R3
R2
R1
C4
C3C2
L1
L2
C1
15
ATA8741 [DATASHEET]
9140E–INDCO–09/14
Figure 8-4. Output Power Measurement ATA8741
C8 3.9pF 4.7pF 5.6pF GRM1885C/
Murata
Frequency deviation of ±16kHz will be
performed using the combination of C8 and
C9
C9 18pF 8.2pF 5.6pF GRM1885C/
Murata
Frequency deviation of ±16kHz will be
performed using the combination of C8 and
C9
T1 BSS83
Q1 9.843750MH
z13.56MHz 13.567187M
Hz
DSX530GK/
KDS
R1 100kΩ100kΩ100kΩ
R2 100kΩ100kΩ100kΩ
R3 10kΩ10kΩ10kΩ
R4 1.8kΩ1.8kΩ1.8kΩ
Table 8-3. Transmitter Pin Cross Reference List
Pin Name Pin Number ATA8401/02/03 Pin Number ATA8741/42/43
CLK 1 8
PA_ENABLE 2 9
ANT2 310
ANT1 411
XTAL 520
VS 621
GND 7 22
ENABLE 823
Note: For the ATA8741, the following points differs in the data sheets:
- The temperature range is limited to –40°C to +85°C
- ESD protection: HBM 2500V, MM 100V, CDM 1000V
- Figure 8-4: Two output power measurement
- For FSK modulation, an additional MOS switch is required
Table 8-2. Bill of Material (Continued)
Component Value
Type/
Manufacturer Note
L1 = 47nH
C2 = 3.3pF
C1 = 1nF
VS
Rin
ANT2
ANT1
ZLopt
Power
meter
50Ω
Z = 50Ω
ATA8741 [DATASHEET]
9140E–INDCO–09/14
16
Table 8-4. Microcontroller Cross Reference List
Pin Name
Pin Number
ATtiny44V
Pin Number
ATA8741/ATA8742/ATA8743
VCC 1 1
PB0 2 2
PB1 3 3
PB3/NRESET 4 4
PB2 5 5
PA7 6 6
PA6/MOSI 7 7
PA5/MISO 813
PA4/USCK 914
PA3/T0 10 15
PA2 11 16
PA1 12 17
PA0 13 18
GND 14 19
Note: For the ATA8741/ATA8742/ATA8743, the following points differs from the Atmel® ATtiny44V datasheet:
- The temperature range is limited to –40°C to +85°C
- The supply voltage range is limited from 2.0V to 4.0V
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Appendix 1: Microcontroller ATtiny24/44/84
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9. Overview
The Atmel® ATtiny24/44/84 is a low-power CMOS 8-bit microcontroller based on the AVR® enhanced RISC architecture. By
executing powerful instructions in a single clock cycle, the Atmel ATtiny24/44/84 achieves throughputs approaching 1MIPS
per MHz allowing the system designer to optimize power consumption versus processing speed.
9.1 Block Diagram
Figure 9-1. Block Diagram
Instruction
Register
Program
Flash
Program
Counter
MCU Control
Register
MCU Status
Register
Timer/
Counter 0
Timer/
Counter 1
Interrupt
Unit
Watchdog
Timer
Timing and
Control
EEPROM Oscillators
Internal
Calibrated
Oscillator
Internal
Oscillator
Instruction
Decoder
Control
Lines
Stack
Pointer
Status
Register
ISP
Interface
Programming
Logic
SRAM
ALU
8-bit Databus
VCC
X
Y
Z
General
Purpose
Registers
GND
Analog
Comparator
Port A Drivers
ADC
+-
Data Register
Port A
Data Dir. Register
Port A
Port B Drivers
PA7-PA0 PB3-PB0
Data Register
Port B
Data Dir. Register
Port B
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The 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®ATtiny24/44/84 provides the following features: 2/4/8K byte of in-system programmable flash, 128/256/512 bytes
EEPROM, 128/256/512 bytes SRAM, 12 general purpose I/O lines, 32 general purpose working registers, a 8-bit
timer/counter with two PWM channels, a 16-bit timer/counter with two PWM channels, internal and external interrupts,
a 8-channel 10-bit ADC, programmable gain stage (1x, 20x) for 12 differential ADC channel pairs, a programmable
watchdog timer with internal oscillator, internal calibrated oscillator, and three software selectable power saving modes. The
idle mode stops the CPU while allowing the SRAM, timer/counter, ADC, analog comparator, and interrupt system to continue
functioning. The power-down mode saves the register contents, disabling all chip functions until the next interrupt or
hardware reset. The ADC noise reduction mode stops the CPU and all I/O modules except 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 high density non-volatile memory technology. The on-chip ISP flash allows the
program memory to be re-programmed in-system through an SPI serial interface, by a conventional non-volatile memory
programmer or by an on-chip boot code running on the AVR core.
The ATtiny24/44/84 AVR is supported with a full suite of program and system development tools including: C compilers,
macro assemblers, program debugger/simulators, in-circuit emulators, and evaluation kits.
9.2 Automotive Quality Grade
The Atmel ATtiny24/44/84 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 ATtiny24/44/84 have been verified during
regular product qualification as per AEC-Q100.
As indicated in the ordering information paragraph, the product is available in only one temperature grade,
9.3 Pin Descriptions
9.3.1 VCC
Supply voltage.
9.3.2 GND
Ground.
9.3.3 Port B (PB3...PB0)
Port B is a 4-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 except PB3 which has the RESET capability. To
use pin PB3 as an I/O pin, instead of RESET pin, program (‘0’) RSTDISBL fuse. 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.
Port B also serves the functions of various special features of the Atmel ATtiny24/44/84 as listed
on Section 19.3 “Alternate Port Functions” on page 68.
9.3.4 RESET
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 Figure 16-1 on page 50. Shorter pulses are not guaranteed to generate a
reset.
Table 9-1. Temperature Grade Identification for Automotive Products
Temperature Temperature Identifier Comments
–40; +125 ZFull automotive temperature range
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9.3.5 Port A (PA7...PA0)
Port A is a 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The port A output buffers have
symmetrical drive characteristics with both high sink and source capability. As inputs, port A pins that are externally pulled
low will source current if the pull-up resistors are activated. The port A pins are tri-stated when a reset condition becomes
active, even if the clock is not running.
Port A has an alternate functions as analog inputs for the ADC, analog comparator, timer/counter, SPI and pin change
interrupt as described in Section 19.3 “Alternate Port Functions” on page 68
10. Resources
A comprehensive set of development tools, drivers and application notes, and datasheets are available for download on
http://www.atmel.com/avr.
11. 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 files and interrupt handling in C is compiler dependent. Please confirm with the C
compiler documentation for more details.
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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12. CPU Core
12.1 Overview
This section discusses the 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.
12.2 Architectural Overview
Figure 12-1. Block Diagram of the AVR Architecture
In order to maximize performance and parallelism, the 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 x 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.
Status and
Control
Interrupt
Unit
Universal
Serial Interface
32 x 8
General
Purpose
Registers
ALU
Data Bus 8-bit
Data
SRAM
Instruction
Register
Instruction
Decoder Watchdog
Timer
Analog
Comparator
EEPROM
I/O Lines
Control Lines
Direct Addressing
Indirect Addressing
Timer/Counter 0
Timer/Counter 1
Program
Counter
Flash
Program
Memory
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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.
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.
12.3 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.
12.4 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.
12.4.1 SREG – AVR Status Register
• 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 76543210
0x3F (0x5F) I T H S V N Z C SREG
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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• 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.
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12.5 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 12-2 shows the structure of the 32 general purpose working registers in the CPU.
Figure 12-2. 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 12-2 on page 24, 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.
7 0 Addr.
R0 0x00
R1 0x01
R2 0x02
…
R13 0x0D
General R14 0x0E
Purpose R15 0x0F
Working R16 0x10
Registers 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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12.5.1 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 12-3 on page 25.
Figure 12-3. 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).
12.6 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 0x60. 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.
12.6.1 SPH and SPL – Stack Pointer High and Low
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
0x3E (0x5E) SP15 SP14 SP13 SP12 SP11 SP10 SP9 SP8 SPH
0x3D (0x5D) 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 Value00000000
00000000
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12.7 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 12-4 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 12-4. The Parallel Instruction Fetches and Instruction Executions
Figure 12-5 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 12-5. Single Cycle ALU Operation
clk
CPU
T1
Register Operands Fetch
Result Write Back
ALU Operation Execute
Total Execution Time
T2 T3 T4
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12.8 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.
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 17. “Interrupts” on page 59. 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.
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.
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.
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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.
12.8.1 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
_SEI(); /* set Global Interrupt Enable */
_SLEEP(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */
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13. Memories
This section describes the different memories in the Atmel® ATtiny24/44/84. The AVR® architecture has two main memory
spaces, the data memory and the program memory space. In addition, the Atmel ATtiny24/44/84 features an EEPROM
memory for data storage. All three memory spaces are linear and regular.
13.1 In-System Re-programmable Flash Program Memory
The Atmel ATtiny24/44/84 contains 2/4/8K byte 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 1024/2048/4096 ×16.
The flash memory has an endurance of at least 10,000 write/erase cycles. The Atmel ATtiny24/44/84 program counter (PC)
is 10/11/12 bits wide, thus addressing the 1024/2048/4096 program memory locations.
Section 28. “Memory Programming” on page 161 contains a detailed description on flash data serial downloading using the
SPI pins.
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 12.7 “Instruction Execution Timing” on page 26.
Figure 13-1. Program Memory Map
13.2 SRAM Data Memory
Figure 13-2 on page 30 shows how the Atmel ATtiny24/44/84 SRAM memory is organized.
The lower 160 data memory locations address both the register file, the I/O memory and the internal data SRAM. The first 32
locations address the register file, the next 64 locations the standard I/O memory, and the last 128/256/512 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, and the 128/256/512 bytes of internal data SRAM in the Atmel
ATtiny24/44/84 are all accessible through all these addressing modes. The register file is described
in Section 12.5 “General Purpose Register File” on page 24.
0x0000
0x03FF/0x07FF/0xFFF
Program Memory
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Figure 13-2. Data Memory Map
13.2.1 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 13-3.
Figure 13-3. On-chip Data SRAM Access Cycles
13.3 EEPROM Data Memory
The Atmel® ATtiny24/44/84 contains 128/256/512 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. For a detailed description of serial data downloading to the
EEPROM, see Section 28.6 “Serial Downloading” on page 164.
13.3.1 EEPROM Read/Write Access
The EEPROM access registers are accessible in the I/O space.
The write access times for the EEPROM are given in Table 13-1 on page 35. 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 13.3.6 “Preventing EEPROM Corruption” on page 33 for details on how to avoid problems in these situations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed.
See Section 13.3.2 “Atomic Byte Programming” on page 31 and Section 13.3.3 “Split Byte Programming” on page 31 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.
32 Registers
Data Memory
0x0000 - 0x001F
0x0020 - 0x005F
0x0060
0x0DF/0x015F/0x025F
64 I/O Registers
Internal SRAM
(128/256/512 x 8)
clk
CPU
T1
Data
Data
RD
WR
Address validCompute Address
Next Instruction
Write
Read
Memory Access Instruction
A
ddress
T2 T3
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13.3.2 Atomic Byte Programming
Using atomic byte programming is the simplest mode. When writing a byte to the EEPROM, the user must write the address
into the EEARL register and data into EEDR register. If the EEPMn bits are zero, writing EEPE (within four cycles after
EEMPE is written) will trigger the erase/write operation. Both the erase and write cycle are done in one operation and the
total programming time is given in Table 1. The EEPE bit remains set until the erase and write operations are completed.
While the device is busy with programming, it is not possible to do any other EEPROM operations.
13.3.3 Split Byte Programming
It is possible to split the erase and write cycle in two different operations. This may be useful if the system requires short
access time for some limited period of time (typically if the power supply voltage falls). In order to take advantage of this
method, it is required that the locations to be written have been erased before the write operation. But since the erase and
write operations are split, it is possible to do the erase operations when the system allows doing time-critical operations
(typically after power-up).
13.3.4 Erase
To erase a byte, the address must be written to EEAR. If the EEPMn bits are 0b01, writing the EEPE (within four cycles after
EEMPE is written) will trigger the erase operation only (programming time is given in table 1). The EEPE bit remains set until
the erase operation completes. While the device is busy programming, it is not possible to do any other EEPROM
operations.
13.3.5 Write
To write a location, the user must write the address into EEAR and the data into EEDR. If the EEPMn bits are 0b10, writing
the EEPE (within four cycles after EEMPE is written) will trigger the write operation only
(programming time is given in table 1). The EEPE bit remains set until the write operation completes. If the location to be
written has not been erased before write, the data that is stored must be considered as lost. While the device is busy with
programming, it is not possible to do any other EEPROM operations.
The calibrated oscillator is used to time the EEPROM accesses. Make sure the oscillator frequency is within the
requirements described in Section 14.10.1 “Oscillator Calibration Register – OSCCAL” on page 43.
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The following code examples show one assembly and one C function for erase, write, or atomic write of 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.
Note: The code examples are only valid for Atmel ATtiny24 and Atmel ATtiny44, using 8-bit addressing mode.
Assembly Code Example
EEPROM_write:
; Wait for completion of previous write
sbic EECR,EEPE
rjmp EEPROM_write
; Set Programming mode
ldi r16, (0<<EEPM1)|(0<<EEPM0)
out EECR, r16
; Set up address (r17) in address register
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 char ucAddress, unsigned char ucData)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set Programming mode */
EECR = (0<<EEPM1)|(0>>EEPM0)
/* Set up address and data registers */
EEARL = ucAddress;
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.
Note: The code examples are only valid for ATtiny24 and ATtiny44, using 8-bit addressing mode.
13.3.6 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 (r17) in address register
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 char ucAddress)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set up address register */
EEARL = ucAddress;
/* Start eeprom read by writing EERE */
EECR |= (1<<EERE);
/* Return data from data register */
return EEDR;
}
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13.4 I/O Memory
The I/O space definition of the Atmel® ATtiny24/44/84 is shown in Section 31. “Register Summary” on page 203.
All Atmel ATtiny24/44/84 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. See 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.
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®, 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.
13.4.1 General Purpose I/O Registers
The Atmel ATtiny24/44/84 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.
13.5 Register Description
13.5.1 EEARH – EEPROM Address Register
• Bits 7..1 – Res: Reserved Bits
These bits are reserved bits in the Atmel ATtiny24/44/84 and will always read as zero.
• Bit 0 – EEAR8: EEPROM Address
The EEPROM address register – EEARH – specifies the most significant bit for EEPROM address in the 512 bytes
EEPROM space for Tiny84. This bit is reserved bit in the ATtiny24/44 and will always read as zero. The initial value of EEAR
is undefined. A proper value must be written before the EEPROM may be accessed.
13.5.2 EEARL – EEPROM Address Register
• Bits 7..0 – EEAR7..0: EEPROM Address
The EEPROM address register – EEARL – specifies the EEPROM address. In the 128 bytes EEPROM space in Atmel
ATiny24 bit 7 is reserved and always read as zero. The EEPROM data bytes are addressed linearly between 0 and
128/256/512. The initial value of EEAR is undefined. A proper value must be written before the EEPROM may be accessed.
Bit 76543210
0x1F (0x3F) –––––––EEAR8EEARH
Read/Write R R R R R R R R/W
Initial Value0000000X
Bit 76543210
0x1E (0x3E) EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEARL
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial ValueXXXXXXXX
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13.5.3 EEDR – EEPROM Data Register
• 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.
13.5.4 EECR – EEPROM Control Register
• Bit 7 – Res: Reserved Bit
This bit is reserved for future use and will always read as 0 in Atme lATtiny24/44/84. For compatibility with future AVR®
devices, always write this bit to zero. After reading, mask out this bit.
• Bit 6 – Res: Reserved Bit
This bit is reserved in the Atmel ATtiny24/44/84 and will always read as zero.
• Bits 5, 4 – EEPM1 and EEPM0: EEPROM
Mode bits
The EEPROM programming mode bits 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 13-1. 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 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 non-volatile memory is ready for programming.
Bit 76543210
0x1D (0x3D) EEDR7 EEDR6 EEDR5 EEDR4 EEDR3 EEDR2 EEDR1 EEDR0 EEDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x1C (0x3C) – – 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
Table 13-1. 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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• Bit 2 – EEMPE: EEPROM Master Program Enable
The EEMPE bit determines whether writing EEPE to one will have effect or not.
When EEMPE is set, setting EEPE within four clock cycles will program 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.
• Bit 1 – EEPE: EEPROM Program Enable
The EEPROM program enable signal EEPE is the programming enable signal to the EEPROM. When EEPE is written, the
EEPROM will be programmed according to the EEPMn bits setting. The EEMPE bit must be written to one before a logical
one is written to EEPE, otherwise no EEPROM write takes place. When the write access time has elapsed, the EEPE bit is
cleared by hardware. 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 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. 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.
13.5.5 GPIOR2 – General Purpose I/O Register 2
13.5.6 GPIOR1 – General Purpose I/O Register 1
13.5.7 GPIOR0 – General Purpose I/O Register 0
Bit 76543210
0x15 (0x35) 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
0x14 (0x34) 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
0x13 (0x33) 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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14. System Clock and Clock Options
14.1 Clock Systems and their Distribution
Figure 14-1 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 15. “Power Management and Sleep Modes” on page 45. The clock systems are
detailed below.
Figure 14-1. Clock Distribution
14.1.1 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.
14.1.2 I/O Clock – clkI/O
The I/O clock is used by the majority of the I/O modules, like timer/counter. 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.
14.1.3 Flash Clock – clkFLASH
The flash clock controls operation of the flash interface. The flash clock is usually active simultaneously with the CPU clock.
Flash and
EEPROM
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
clkADC
clkCPU
clkFLASH
Clock
Multiplexer
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14.1.4 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.
14.2 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.
The various choices for each clocking option is given in the following sections. When the CPU wakes up from power-down or
power-save, the selected clock source is used to time the start-up, ensuring stable oscillator operation before instruction
execution starts. When the CPU starts from reset, there is an additional delay allowing the power to reach a stable level
before commencing normal operation. The watchdog oscillator is used for timing this real-time part of the start-up time. The
number of WDT oscillator cycles used for each time-out is shown in Table 14-2.
14.3 Default Clock Source
The device is shipped with CKSEL = “0010”, SUT = “10”, and CKDIV8 programmed. The default clock source setting is
therefore the internal RC oscillator running at 8.0MHz with longest start-up time and an initial system clock prescaling of 8,
resulting in 1.0MHz system clock. This default setting ensures that all users can make their desired clock source setting
using an in-system or high-voltage programmer.
Table 14-1. Device Clocking Options Select(1)
Device Clocking Option CKSEL3..0
External clock 0000
Calibrated internal RC oscillator 8.0MHz 0010
Watchdog oscillator 128kHz 0100
External L low-frequency oscillator 0110
External crystal/ceramic resonator 1000-1111
Reserved 0101, 0111, 0011,0001
Note: 1. For all fuses “1” means unprogrammed while “0” means programmed.
Table 14-2. Number of Watchdog Oscillator Cycles
Typ Time-out Number of Cycles
4ms 512
64ms 8K (8,192)
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14.4 Crystal Oscillator
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 14-2 Either a quartz
crystal or a ceramic resonator may be used.
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 14-3 on page 39. For ceramic resonators, the
capacitor values given by the manufacturer should be used.
Figure 14-2. Crystal Oscillator Connections
The 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 14-3.
Table 14-3. Crystal Oscillator Operating Modes
CKSEL3..1 Frequency Range (MHz)
Recommended Range for Capacitors C1 and C2 for Use
with Crystals (pF)
100(1) 0.4 - 0.9 –
101 0.9 - 3.0 12 - 22
110 3.0 - 8.0 12 - 22
111 8.0 - 12 - 22
Note: 1. This option should not be used with crystals, only with ceramic resonators.
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 14-4 on page 40.
14.5 Low-frequency Crystal Oscillator
To use a 32.768kHz watch crystal as the clock source for the device, the low-frequency crystal oscillator must be selected by
setting CKSEL fuses to ‘0110’. The crystal should be connected as shown in Figure 14-2 on page 39. See the 32kHz crystal
oscillator application note for details on oscillator operation and how to choose appropriate values for C1 and C2.
When this oscillator is selected, start-up times are determined by the SUT fuses as shown in Table 14-5.
Table 14-4. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0 SUT1..0
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset
(VCC = 5.0V) Recommended Usage
000 258CK(1) 14CK + 4.1ms Ceramic resonator, fast rising
power
001 258CK(1) 14CK + 65ms Ceramic resonator, slowly rising
power
010 1KCK(2) 14CK Ceramic resonator, BOD
enabled
011 1KCK(2) 14CK + 4.1ms Ceramic resonator, fast rising
power
100 1KCK(2) 14CK + 65ms Ceramic resonator, slowly rising
power
101 16KCK 14CK Crystal oscillator, BOD enabled
110 16KCK 14CK + 4.1ms Crystal oscillator, fast rising
power
111 16KCK 14CK + 65ms Crystal oscillator, slowly rising
power
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 14-5. Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
SUT1..0
Start-up Time from Power
Down and Power Save
Additional Delay from Reset
(VCC = 5.0V) Recommended usage
00 1KCK(1) 4ms Fast rising power or BOD enabled
01 1KCK(1) 64ms Slowly rising power
10 32KCK 64ms Stable frequency at start-up
11 Reserved
Note: 1. These options should only be used if frequency stability at start-up is not important for the application.
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14.6 Calibrated Internal RC Oscillator
By default, the internal RC oscillator provides an approximate 8MHz clock. Though voltage and temperature dependent, this
clock can be very accurately calibrated by the user. See Table 29-1 on page 177
and Section 30.9 “Internal Oscillator Speed” on page 197 for more details. The device is shipped with the CKDIV8 fuse
programmed. See Section 14.9 “System Clock Prescaler” on page 43 for more details.
This clock may be selected as the system clock by programming the CKSEL fuses as shown in Table 14-6. If selected, it will
operate with no external components. During reset, hardware loads the pre-programmed calibration value into the OSCCAL
register and thereby automatically calibrates the RC oscillator. The accuracy of this calibration is shown as factory calibration
in Table 29-1 on page 177.
By changing the OSCCAL register from SW, see Section 14.10.1 “Oscillator Calibration Register – OSCCAL” on page 43, it
is possible to get a higher calibration accuracy than by using the factory calibration. The accuracy of this calibration is shown
as user calibration in Table 29-1 on page 177.
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 the Section 28.4 “Calibration Byte” on page 164.
When this oscillator is selected, start-up times are determined by the SUT fuses as shown in Table 14-7.
.
Table 14-6. Internal Calibrated RC Oscillator Operating Modes
CKSEL3..0 Nominal Frequency
0010(1) 8.0MHz
Note: 1. The device is shipped with this option selected.
Table 14-7. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
SUT1..0
Start-up Time
from Power-down
Additional Delay from Reset
(VCC = 5.0V) Recommended Usage
00 6CK 14CK BOD enabled
01 6CK 14CK + 4ms Fast rising power
10(1) 6CK 14CK + 64ms Slowly rising power
11 Reserved
Note: 1. The device is shipped with this option selected.
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14.7 External Clock
To drive the device from an external clock source, CLKI should be driven as shown in Figure 14-3. To run the device on an
external clock, the CKSEL fuses must be programmed to “0000”.
Figure 14-3. External Clock Drive Configuration
When this clock source is selected, start-up times are determined by the SUT fuses as shown in Table 14-8.
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. It is required to ensure that the MCU is kept in reset during such changes in the clock frequency.
Note that the system clock prescaler can be used to implement run-time changes of the internal clock frequency while still
ensuring stable operation. See to Section 14.9 “System Clock Prescaler” on page 43 for details.
14.8 128 kHz 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 “0100”.
When this clock source is selected, start-up times are determined by the SUT fuses as shown in Table 14-9.
Table 14-8. Start-up Times for the External Clock Selection
SUT1..0
Start-up Time from Power-down and
Power-save Additional Delay from Reset Recommended Usage
00 6CK 14CK BOD enabled
01 6CK 14CK + 4ms Fast rising power
10 6CK 14CK + 64ms Slowly rising power
11 Reserved
CLKI
GND
External
Clock
Signal
Table 14-9. Start-up Times for the 128 kHz Internal Oscillator
SUT1..0
Start-up Time from Power-down and
Power-save Additional Delay from Reset Recommended Usage
00 6CK 14CK BOD enabled
01 6CK 14CK + 4ms Fast rising power
10 6CK 14CK + 64ms Slowly rising power
11 Reserved
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14.9 System Clock Prescaler
The Atmel® ATtiny24/44/84 system clock can be divided by setting the clock prescale register – CLKPR. This feature can be
used to decrease 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 14-10.
14.9.1 Switching Time
When switching between prescaler settings, the system clock prescaler ensures that no glitches occur in the clock system
and 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 another 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.
14.10 Register Description
14.10.1 Oscillator Calibration Register – OSCCAL
The oscillator calibration register is used to trim the calibrated internal RC oscillator to remove process variations from the
oscillator frequency. A pre-programmed calibration value is automatically written to this register during chip reset, giving the
factory calibrated frequency as specified in Table 29-1 on page 177. The application software can write this register to
change the oscillator frequency. The oscillator can be calibrated to frequencies as specified in Table 29-1 on page 177.
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.
14.10.2 Clock 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 simultaniosly written to zero. CLKPCE is cleared by hardware four cycles after it is written or when
the 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
0x31 (0x51) 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
Bit 76543210
0x26 (0x46) 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 6..4 – Res: Reserved Bits
These bits are reserved bits in the Atmel® ATtiny24/44/84 and will always read as zero.
• 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 14-10.
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.
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 eight 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.
Table 14-10. 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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15. 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.
15.1 Sleep Modes
Figure 14-1 on page 37 presents the different clock systems in the Atmel® ATtiny24/44/84, and their distribution. The figure
is helpful in selecting an appropriate sleep mode. Table 15-1 shows the different sleep modes and their wake up sources
To enter any of the three sleep modes, the SE bit in MCUCR must be written to logic one and a SLEEP instruction must be
executed. The SM1..0 bits in the MCUCR register select which sleep mode (idle, ADC noise reduction,
standby or power-down) will be activated by the SLEEP instruction. See Table 15-2 on page 47 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 vector.
15.2 Idle Mode
When the SM1..0 bits are written to 00, the SLEEP instruction makes the MCU enter idle mode, stopping the CPU but
allowing analog comparator, ADC, timer/counter, 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. 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.
15.3 ADC Noise Reduction Mode
When the SM1..0 bits are written to 01, the SLEEP instruction makes the MCU enter ADC noise reduction mode, stopping
the CPU but allowing the ADC, the external interrupts, and the Watchdog to continue operating (if enabled). This sleep mode
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 form the ADC conversion complete interrupt, only an
external reset, a watchdog reset, a brown-out reset, an SPM/EEPROM ready interrupt, an external level interrupt on INT0 or
a pin change interrupt can wake up the MCU from ADC noise reduction mode.
Table 15-1. Active Clock Domains and Wake-up Sources in the Different Sleep Modes
Active Clock Domains Oscillators Wake-up Sources
Sleep Mode
clkCPU
clkFLASH
clkIO
clkADC
Main Clock
Source Enabled
INT0 and
Pin Change
SPM/
EEPROM
Ready
ADC
Other I/O
Watchdog
Interrupt
Idle X X X X X X X X
ADC noise
Reduction X X X(1) X X X
Power-down X(1) X
Stand-by(2) X X(1)
Note: 1. For INT0, only level interrupt.
2. Only recommended with external crystal or resonator selected as clock source
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15.4 Power-down Mode
When the SM1..0 bits are written to 10, the SLEEP instruction makes the MCU enter power-down mode. In this mode, the
oscillator is stopped, while the external interrupts, and the watchdog continue operating (if enabled). Only an external reset,
a watchdog reset, a brown-out reset, an external level interrupt on INT0, or a pin change interrupt can wake up the MCU.
This sleep mode 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. See Section 18. “External Interrupts” on page 61 for details
15.5 Standby Mode
When the SM1..0 bits are 11 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.
15.6 Power Reduction Register
The power reduction register (PRR), see Section 15.8.2 “PRR – Power Reduction Register” on page 48, provides a method
to stop the clock to individual peripherals to reduce power consumption. The current state of the peripheral is frozenand 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 30.4 “Power-down Supply Current” on page 188 for examples. In all other sleep modes, the clock is already stopped.
15.7 Minimizing Power Consumption
There are several issues 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.
15.7.1 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.
See Section 25. “Analog to Digital Converter” on page 136 for details on ADC operation.
15.7.2 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 the 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. See
Section 24. “Analog Comparator” on page 133 for details on how to configure the analog comparator.
15.7.3 Brown-out Detector
If the brown-out detector is not needed in 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.
See Section 16.5 “Brown-out Detection” on page 52 for details on how to configure the brown-out detector.
15.7.4 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.
See Section 16.7 “Internal Voltage Reference” on page 53 for details on the start-up time.
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15.7.5 Watchdog Timer
If the watchdog timer is not needed in the application, this 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. See Section 16.8 “Watchdog Timer” on page 54 for details on how to configure
the watchdog timer.
15.7.6 Port Pins
When entering a sleep mode, all port pins should be configured to use minimum power. The most important thing 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. See the
Section 19.2.5 “Digital Input Enable and Sleep Modes” on page 68 for details on which pins are enabled. If the input buffer is
enabled and the input signal is left floating or has 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 register (DIDR0). See Section 25.10.5 “DIDR0 – Digital Input Disable Register 0” on page 154 for details.
15.8 Register Description
15.8.1 MCUCR – MCU Control Register
The MCU Control Register contains control bits for power management.
• Bit 5 – 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.
• Bits 4, 3 – SM1..0: Sleep Mode Select Bits 2..0
These bits select between the three available sleep modes as shown in Table 15-2 on page 47.
• Bit 2 – Res: Reserved Bit
This bit is a reserved bit in the Atmel® ATtiny24/44/84 and will always read as zero.
Bit 76543210
–PUD SE SM1 SM0 — ISC01 ISC00 MCUCR
Read/Write R R/W R/W R/W R/W R R/W R/W
Initial Value00000000
Table 15-2. Sleep Mode Select
SM1 SM0 Sleep Mode
0 0 Idle
0 1 ADC noise reduction
1 0 Power-down
1 1 Standby(1)
Note: 1. Only recommended with external crystal or resonator selected as clock source
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15.8.2 PRR – Power Reduction Register
• Bits 7, 6, 5, 4- Res: Reserved Bits
These bits are reserved bits in the Atmel® ATtiny24/44/84 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- 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 1 - PRUSI: Power Reduction USI
Writing a logic one to this bit shuts down the USI by stopping the clock to the module. When waking up the USI again, the
USI 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 76543 2 10
– – – – PRTIM1 PRTIM0 PRUSI PRADC PRR
Read/Write R R R R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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16. System Control and Reset
16.1 Resetting the AVR
During reset, all I/O registers are set to their initial values, and the program starts execution from the reset vector. The
instruction placed at the reset vector must be a 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. The circuit diagram in Figure 16-1 shows the reset logic. Table 16-1 on page 51 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 14.2 “Clock Sources” on page 38.
16.2 Reset Sources
The ATtiny24/44/84 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 when RESET function is enabled.
●Watchdog reset. The MCU is reset when the watchdog timer period expires and the watchdog 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 16-1. Reset Logic
Power-on Reset
Circuit
Brown-out
Reset Circuit
MCU Status
Register (MCUSR)
Reset Circuit
Pull-up Resistor
BODLEVEL [1..0]
SQ
R
DATA BUS
CK
SUT[1:0]
CKSEL[1:0]
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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16.3 Power-on Reset
A power-on reset (POR) pulse is generated by an on-chip detection circuit.
The detection level is defined in Section 29.5 “System and Reset Characterizations” on page 178. 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.
Figure 16-2. MCU Start-up, RESET Tied to VCC
Figure 16-3. MCU Start-up, RESET Extended Externally
Table 16-1. Power On Reset Specifications
Parameter Symbol Min Typ Max Unit
Power-on reset threshold voltage (rising) VPOT
1.1 1.4 1.7 V
Power-on reset threshold voltage (falling)(1) 0.8 1.3 1.6 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 0.9VCC V
Note: 1. Before rising, the supply has to be between VPORMIN and VPORMAX to ensure a reset.
V
CCRR
RESET
Internal
Reset
Time-out
tTOUT
VPORMAX
VPORMIN
VRST
VCC
RESET
Internal
Reset
Time-out
VRST
tTOUT
VPOT
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16.4 External Reset
An external reset is generated by a low level on the RESET pin if enabled. Reset pulses longer than the minimum pulse
width (see Section 29.5 “System and Reset Characterizations” on page 178) 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.
Figure 16-4. External Reset During Operation
16.5 Brown-out Detection
Atmel® ATtiny24/44/84 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.
When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in Figure 16-5), the brown-out reset is
immediately activated. When VCC increases above the trigger level (VBOT+ in Figure 16-5), 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 Section 29.5 “System and Reset Characterizations” on page 178.
Figure 16-5. Brown-out Reset During Operation
tTOUT
RESET
VCC
Internal
Reset
Time-out
V
RST
VBOT-
VBOT+
tTOUT
VCC
RESET
Internal
Reset
Time-out
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16.6 Watchdog 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. See Section 16.8 “Watchdog Timer” on page 54 for details on
operation of the watchdog timer.
Figure 16-6. Watchdog Reset During Operation
16.7 Internal Voltage Reference
Atmel® ATtiny24/44/84 features an internal bandgap reference. This reference is used for brown-out detection, and it can be
used as an input to the analog comparator or the ADC.
16.7.1 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 Section 29.5 “System and Reset Characterizations” on page 178. 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] fuse).
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.
1 CK Cycle
VCC
RESET
Internal
Reset
RESET
Time-out
WDT
Time-out
tTOUT
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16.8 Watchdog Timer
The watchdog timer is clocked from an on-chip oscillator which runs at 128kHz. By controlling the watchdog timer prescaler,
the watchdog reset interval can be adjusted as shown in Table 16-4 on page 57. The WDR – watchdog reset – instruction
resets the watchdog timer. The watchdog timer is also reset when it is disabled and when a chip reset occurs. Ten different
clock cycle periods can be selected to determine the reset period. If the reset period expires without another watchdog reset,
the Atmel ATtiny24/44/84 resets and executes from the reset vector. For timing details on the watchdog reset,
refer to Table 16-4 on page 57.
The watchdog timer can also be configured to generate an interrupt instead of a reset. This can be very helpful when using
the watchdog to wake-up from power-down.
To prevent unintentional disabling of the watchdog or unintentional change of time-out period, two different safety levels are
selected by the fuse WDTON as shown in Table 16-2
See Section 16.9 “Timed Sequences for Changing the Configuration of the Watchdog Timer” on page 54 for details.
Figure 16-7. Watchdog Timer
16.9 Timed Sequences for Changing the Configuration of the Watchdog Timer
The sequence for changing configuration differs slightly between the two safety levels. Separate procedures are described
for each level.
16.9.1 Safety Level 1
In this mode, the watchdog timer is initially disabled, but can be enabled by writing the WDE bit to one without any restriction.
A timed sequence is needed when disabling an enabled watchdog timer. To disable an enabled watchdog timer, the
following procedure must be followed:
1. In the same operation, write a logic one to 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, in the same operation, write the WDE and WDP bits as desired, but with the
WDCE bit cleared.
Table 16-2. WDT Configuration as a Function of the Fuse Settings of WDTON
WDTON Safety Level WDT Initial State How to Disable the WDT How to Change Time-out
Unprogrammed 1Disabled Timed sequence No limitations
Programmed 2Enabled Always enabled Timed sequence
OSC/2K
OSC/4K
OSC/8K
OSC/16K
OSC/32K
OSC/64K
OSC/128K
OSC/256K
OSC/512K
OSC/1024K
Watchdog
Prescaler
MCU Reset
WDP0
Watchdog
Reset
WDP1
WDP2
WDP3
WDE
128kHz
Oscillator
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16.9.2 Safety Level 2
In this mode, the watchdog timer is always enabled, and the WDE bit will always read as one. A timed sequence is needed
when changing the watchdog time-out period. To change the watchdog time-out, the following procedure must be followed:
1. In the same operation, write a logical one to WDCE and WDE. Even though the WDE always is set, the WDE must
be written to one to start the timed sequence.
2. Within the next four clock cycles, in the same operation, write the WDP bits as desired, but with the WDCE bit
cleared. The value written to the WDE bit is irrelevant.
16.10 Register Description
16.10.1 MCUSR – MCU Status Register
The MCU status register provides information on which reset source caused an MCU reset.
• Bits 7..4 – Res: Reserved Bits
These bits are reserved bits in the Atmel ATtiny24/44/84 and will always read as zero.
• Bit 3 – WDRF: Watchdog Reset Flag
This bit is set if a watchdog 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.
Bit 76543210
0x34 (0x54) ––––WDRFBORFEXTRFPORFMCUSR
Read/Write RRRRR/WR/WR/WR/W
Initial Value0000 See Bit Description
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16.10.2 WDTCSR – Watchdog Timer Control and Status Register
• Bit 7 – WDIF: Watchdog Timeout 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 Timeout Interrupt Enable
When this bit is written to one, WDE is cleared, and the I-bit in the status register is set, the watchdog time-out interrupt is
enabled. In this mode the corresponding interrupt is executed instead of a reset if a time-out in the watchdog timer occurs.
If WDE is set, WDIE is automatically cleared by hardware when a time-out occurs. This is useful for keeping the watchdog
reset security while using the interrupt. After the WDIE bit is cleared, the next time-out will generate a reset. To avoid the
watchdog reset, WDIE must be set after each interrupt.
• Bit 4 – WDCE: Watchdog Change Enable
This bit must be set when the WDE bit is written to logic zero. Otherwise, the watchdog will not be disabled. Once written to
one, hardware will clear this bit after four clock cycles. See the description of the WDE bit for a watchdog disable procedure.
This bit must also be set when changing the prescaler bits.
See Section 16.9 “Timed Sequences for Changing the Configuration of the Watchdog Timer” on page 54.
• Bit 3 – WDE: Watchdog Enable
When the WDE is written to logic one, the watchdog timer is enabled, and if the WDE is written to logic zero, the Watchdog
Timer function is disabled. WDE can only be cleared if the WDCE bit has logic level one. To disable an enabled Watchdog
Timer, the following procedure must be followed:
1. In the same operation, write a logic one to WDCE and WDE. A logic one must be written to WDE even though it is
set to one before the disable operation starts.
2. Within the next four clock cycles, write a logic 0 to WDE. This disables the watchdog.
In safety level 2, it is not possible to disable the watchdog timer, even with the algorithm described above.
See Section 16.9 “Timed Sequences for Changing the Configuration of the Watchdog Timer” on page 54.
In safety level 1, WDE is overridden by WDRF in MCUSR. See Section 16.10.1 “MCUSR – MCU Status Register” on page
55 for description of WDRF. This means that WDE is always set when WDRF is set. To clear WDE, WDRF must be cleared
before disabling the watchdog with the procedure described above. This feature ensures multiple resets during conditions
causing failure, and a safe start-up after the failure.
Note: If the watchdog timer is not going to be used in the application, it is important to go through a watchdog disable
procedure in the initialization of the device. If the watchdog is accidentally enabled, for example by a runaway
pointer or brown-out condition, the device will be reset, which in turn will lead to a new watchdog reset. To
avoid this situation, the application software should always clear the WDRF flag and the WDE control bit in the
initialization routine.
Bit 76543210
0x21 (0x41) 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 Value 0 0 0 0 X 0 0 0
Table 16-3. Watchdog Timer Configuration
WDE WDIE Watchdog Timer State Action on Time-out
0 0 Stopped None
0 1 Running Interrupt
1 0 Running Reset
1 1 Running Interrupt
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• Bits 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 enabled. The different prescaling
values and their corresponding time-out periods are shown in Table 16-4.
Table 16-4. Watchdog Timer Prescale Select
WDP3 WDP2 WDP1 WDP0 Number of WDT Oscillator Cycles
Typical Time-out at
VCC = 5.0V
0 0 0 0 2Kcycles 16ms
0 0 0 1 4Kcycles 32ms
0 0 1 0 8Kcycles 64ms
0 0 1 1 16Kcycles 0.125s
0 1 0 0 32Kcycles 0.25
0 1 0 1 64Kcycles 0.5s
0 1 1 0 128Kcycles 1.0s
0 1 1 1 256Kcycles 2.0s
1 0 0 0 512Kcycles 4.0s
1 0 0 1 1024Kcycles 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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The following code example shows one assembly and one C function for turning off the WDT. The example assumes that
interrupts are controlled (e.g., by disabling interrupts globally) so that no interrupts will occur during execution of these
functions.
Note: 1. See Section 11. “About Code Examples” on page 20.
Assembly Code Example(1)
WDT_off:
WDR
; Clear WDRF in MCUSR
ldi r16, (0<<WDRF)
out MCUSR, r16
; Write logical one to WDCE and WDE
; Keep old prescaler setting to prevent unintentional Watchdog Reset
in r16, WDTCR
ori r16, (1<<WDCE)|(1<<WDE)
out WDTCR, r16
; Turn off WDT
ldi r16, (0<<WDE)
out WDTCR, r16
ret
C Code Example(1)
void WDT_off(void)
{
_WDR();
/* Clear WDRF in MCUSR */
MCUSR = 0x00
/* Write logical one to WDCE and WDE */
WDTCR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCR = 0x00;
}
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17. Interrupts
This section describes the specifics of the interrupt handling as performed in Atmel® ATtiny24/44/84. For a general
explanation of the AVR® interrupt handling, see Section 12.8 “Reset and Interrupt Handling” on page 27.
17.1 Interrupt Vectors
Table 17-1. Reset and Interrupt Vectors
Vector No. Program Address Source Interrupt Definition
10x0000 RESET External pin, power-on reset, brown-out reset,
watchdog reset
20x0001 INT0 External interrupt request 0
30x0002 PCINT0 Pin change interrupt request 0
40x0003 PCINT1 Pin change interrupt request 1
50x0004 WDT Watchdog time-out
60x0005 TIMER1 CAPT Timer/Counter1 capture event
70x0006 TIMER1 COMPA Timer/Counter1 compare match A
80x0007 TIMER1 COMPB Timer/Counter1 compare match B
90x0008 TIMER1 OVF Timer/Counter0 overflow
10 0x0009 TIMER0 COMPA Timer/Counter0 compare match A
11 0x000A TIMER0 COMPB Timer/Counter0 compare match B
12 0x000B TIMER0 OVF Timer/Counter0 overflow
13 0x000C ANA_COMP Analog comparator
14 0x000D ADC ADC conversion complete
15 0x000E EE_RDY EEPROM ready
16 0x000F USI_START USI START
17 0x0010 USI_OVF USI overflow
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If the program never enables an interrupt source, the interrupt vectors are not used, and regular program code can be placed
at these locations. The most typical and general program setup for the reset and interrupt vector addresses in
ATtiny24/44/84 is:
Address Labels Code Comments
0x0000 rjmp RESET ; Reset Handler
0x0001 rjmp EXT_INT0 ; IRQ0 Handler
0x0002 rjmp PCINT0 ; PCINT0 Handler
0x0003 rjmp PCINT1 ; PCINT1 Handler
0x0004 rjmp WATCHDOG ; Watchdog Interrupt Handler
0x0005 rjmp TIM1_CAPT ; Timer1 Capture Handler
0x0006 rjmp TIM1_COMPA ; Timer1 Compare A Handler
0x0007 rjmp TIM1_COMPB ; Timer1 Compare B Handler
0x0008 rjmp TIM1_OVF ; Timer1 Overflow Handler
0x0009 rjmp TIM0_COMPA ; Timer0 Compare A Handler
0x000A rjmp TIM0_COMPB ; Timer0 Compare B Handler
0x000B rjmp TIM0_OVF ; Timer0 Overflow Handler
0x000C rjmp ANA_COMP ; Analog Comparator Handler
0x000D rjmp ADC ; ADC Conversion Handler
0x000E rjmp EE_RDY ; EEPROM Ready Handler
0x000F rjmp USI_STR ; USI STart Handler
0x0010 rjmp USI_OVF ; USI Overflow Handler
;
0x0011 RESET: ldi r16, high(RAMEND); Main program start
0x0012 out SPH,r16 ; Set Stack Pointer to top of RAM
0x0013 ldi r16, low(RAMEND)
0x0014 out SPL,r16
0x0015 sei ; Enable interrupts
0x0016 <instr> xxx
... ... ... ...
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18. External Interrupts
The external interrupts are triggered by the INT0 pin or any of the PCINT11..0 pins. Observe that, if enabled, the interrupts
will trigger even if the INT0 or PCINT11..0 pins are configured as outputs. This feature provides a way of generating a
software interrupt. Pin change 0 interrupts PCI0 will trigger if any enabled PCINT7..0 pin toggles. Pin change 1 interrupts
PCI1 will trigger if any enabled PCINT11..8 pin toggles. The PCMSK0 and PCMSK1 registers control which pins contribute
to the pin change interrupts. Pin change interrupts on PCINT11..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 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 MCU control register – MCUCR. When the INT0 interrupt is enabled and is configured as level triggered, the interrupt
will trigger as long as the pin is held low. Note that recognition of falling or rising edge interrupts on INT0 requires the
presence of an I/O clock, described in Section 14.1 “Clock Systems and their Distribution” on page 37. Low level interrupt on
INT0 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 14. “System Clock and Clock Options” on page 37.
18.1 Pin Change Interrupt Timing
An example of timing of a pin change interrupt is shown in Figure 18-1.
Figure 18-1. Timing of Pin Change Interrupts
clk
clk
pin_lat
pin_sync
PCINT(0)
PCINT(0)
pcint_syn
pcint_setflag
PCIF
pin_lat pin_sync pcint_sync
x
0
clk
pcint_setflag
PCINT(0) in PCMSK(x)
PCINT(0)
PCIF
pcint_in_(0)
DQ
LE
DQ
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18.2 Register Description
18.2.1 MCUCR – MCU Control Register
The External Interrupt Control Register A contains control bits for interrupt sense control.
• Bits 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 18-1. 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.
18.2.2 GIMSK – General Interrupt Mask Register
• Bits 7, 3..0 – Res: Reserved Bits
These bits are reserved bits in the Atmel® ATtiny24/44/84 and will always read as zero.
• Bit 6 – 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.
• Bit 5 – 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 PCINT11..8 pin will cause an interrupt. The corresponding interrupt of pin change interrupt request is
executed from the PCI1 interrupt vector. PCINT11..8 pins are enabled individually by the PCMSK1 register.
• Bit 4– 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.
Bit 76543210
0x35 (0x55) –PUD SE SM1 SM0 – ISC01 ISC00 MCUCR
Read/Write R R/W R/W R/W R/W R R/W R/W
Initial Value00000000
Table 18-1. 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.
Bit 76543210
0x3B (0x5B) – INT0 PCIE1 PCIE0 – – – – GIMSK
Read/Write R R/W R/W R/w R R R R
Initial Value00000000
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18.2.3 GIFR – General Interrupt Flag Register
• Bits 7, 3..0 – Res: Reserved Bits
These bits are reserved bits in the Atmel® ATtiny24/44/84 and will always read as zero.
• Bit 6 – 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 GIMSK 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 5 – PCIF1: Pin Change Interrupt Flag 1
When a logic change on any PCINT11..8 pin triggers an interrupt request, PCIF1 becomes set (one). If the I-bit in SREG and
the PCIE1 bit in GIMSK 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 4– PCIF0: Pin Change Interrupt Flag 0
When a logic change on any PCINT7..0 pin triggers an interrupt request, PCIF becomes set (one). If the I-bit in SREG and
the PCIE0 bit in GIMSK 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.
18.2.4 PCMSK1 – Pin Change Mask Register 1
• Bits 7, 4– Res: Reserved Bits
These bits are reserved bits in the ATtiny24/44/84 and will always read as zero.
• Bits 3..0 – PCINT11..8: Pin Change Enable Mask 11..8
Each PCINT11..8 bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT11..8 is set and
the PCIE1 bit in GIMSK is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT11..8 is cleared, pin
change interrupt on the corresponding I/O pin is disabled.
18.2.5 PCMSK0 – Pin Change Mask Register 0
• Bits 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 GIMSK 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.
Bit 76543210
0x3A (0x5A – INTF0 PCIF1 PCIF0 – – – – GIFR
Read/Write R R/W R/W R/W R R R R
Initial Value00000000
Bit 7 6 5 4 3 2 1 0
0x20 (0x40) – – – – PCINT11 PCINT10 PCINT9 PCINT8 PCMSK1
Read/Write R R R R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
0x12 (0x32) 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 Value 0 0 0 0 0 0 0 0
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19. I/O Ports
19.1 Overview
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 19-1. See Section 29. “Electrical Characteristics” on page 175 for a complete list of
parameters.
Figure 19-1. 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 2 “EXT_CLOCK = external clock is selected as system clock.” on page 76.
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 19.2 “Ports as General Digital I/O” on page 65. 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 19.3 “Alternate Port Functions” on page 68. 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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19.2 Ports as General Digital I/O
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 19-2 shows a functional description of one I/O-
port pin, here generically called Pxn.
Figure 19-2. 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.
19.2.1 Configuring the Pin
Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown
in Section 2 “EXT_CLOCK = external clock is selected as system clock.” on page 76, 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
Pxn
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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19.2.2 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.
19.2.3 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} = 0b10) as an intermediate step.
Table 19-1 summarizes the control signals for the pin value.
19.2.4 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 19-2 on page 65, 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 19-3 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 19-3. 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 19-1. 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 19-4. 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 one system clock period.
Figure 19-4. Synchronization when Reading a Software Assigned Pin Value
The following code example shows how to set port A pins 0 and 1 high, 2 and 3 low, and define the port pins from 4 to 5 as
input with a pull-up assigned to port pin 4. 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 and 4, 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<<PA4)|(1<<PA1)|(1<<PA0)
ldi r17,(1<<DDA3)|(1<<DDA2)|(1<<DDA1)|(1<<DDA0)
out PORTA,r16
out DDRA,r17
; Insert nop for synchronization
nop
; Read port pins
in r16,PINA
...
C Code Example
unsigned char i;
...
/* Define pull-ups and set outputs high */
/* Define directions for port pins */
PORTA = (1<<PA4)|(1<<PA1)|(1<<PA0);
DDRA = (1<<DDA3)|(1<<DDA2)|(1<<DDA1)|(1<<DDA0);
/* Insert nop for synchronization*/
_NOP();
/* Read port pins */
i = PINA;
...
System CLK
Instructions
SYNC Latch
PINxn
r16
r17
out PORTx, r16 nop
0x00 0xFF
0xFF
in r17, PINx
tpd
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19.2.5 Digital Input Enable and Sleep Modes
As shown in Figure 19-2 on page 65, 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 19.3 “Alternate Port Functions” on page 68.
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.
19.2.6 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
pulldown. 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.
19.3 Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. Figure 19-5 on page 69 shows how the port
pin control signals from the simplified Figure 19-2 on page 65 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 19-5. 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
Pxn
CLR
RESET
Synchronizer
DATA BUS
PORTxn
Q
0
1
Q
L
DSET
CLR CLR
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
CLKI/O
DIxn
AIOxn
CLK:I/O
DIEOVxn
DIEOExn
PVOExn
DDOVxn
PVOVxn
0
1
PUOExn
PUOVxn
0
1
DDOExn
SLEEP
PUD
WDx
D
QCLR
DDxn
Q
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Table 19-2 on page 70 summarizes the function of the overriding signals. The pin and port indexes
from Figure 19-5 on page 69 are not shown in the succeeding tables. The overriding signals are generated internally in the
modules having the alternate function.
Table 19-2. 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.
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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.
19.3.1 Alternate Functions of Port A
The port A pins with alternate function are shown in Table 19-7 on page 74.
• Port A, Bit 0 – ADC0/AREF/PCINT0
ADC0: Analog to digital converter, channel 0.
AREF: External analog reference for ADC. Pullup and output driver are disabled on PA0 when the pin is used as an external
reference or internal voltage reference with external capacitor at the AREF pin by setting (one) the bit REFS0 in the ADC
multiplexer selection register (ADMUX).
PCINT0: pin change interrupt source 0. The PA0 pin can serve as an external interrupt source for pin change interrupt 0.
Table 19-3. Port A Pins Alternate Functions
Port Pin Alternate Function
PA0
ADC0: ADC input channel 0.
AREF: External analog reference.
PCINT0: Pin change interrupt 0 source 0.
PA1
ADC1: ADC input channel 1.
AIN0: Analog comparator positive input.
PCINT1:Pin change interrupt 0 source 1.
PA2
ADC2: ADC input channel 2.
AIN1: Analog comparator negative input.
PCINT2: Pin change interrupt 0 source 2.
PA3
ADC3: ADC input channel 3.
T0: Timer/Counter0 counter source.
PCINT3: Pin change interrupt 0 source 3.
PA4
ADC4: ADC input channel 4.
USCK:USI clock three wire mode.
SCL: USI clock two wire mode.
T1: Timer/Counter1 counter source.
PCINT4: Pin change interrupt 0 source 4.
PA5
ADC5: ADC input channel 5.
DO: USI data output three wire mode.
OC1B: Timer/counter1 compare match B output.
PCINT5: Pin change interrupt 0 source 5.
PA6
ADC6: ADC input channel 6.
DI: USI data input three wire mode.
SDA: USI data input two wire mode.
OC1A: Timer/Counter1 compare match A output.
PCINT6: Pin change interrupt 0 source 6.
PA7
ADC7: ADC input channel 7.
OC0B: Timer/Counter0 compare match B output.
ICP1: Timer/Counter1 input capture pin.
PCINT7: Pin change interrupt 0 source 7.
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• Port A, Bit 1 – ADC1/AIN0/PCINT1
ADC1: Analog to digital converter, channel 1.
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.
PCINT1: Pin change interrupt source 1. The PA1 pin can serve as an external interrupt source for pin change interrupt 0.
• Port A, Bit 2 – ADC2/AIN1/PCINT2
ADC2: Analog to digital converter, channel 2.
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.
PCINT2: Pin change Interrupt source 2. The PA2 pin can serve as an external interrupt source for pin change interrupt 0.
• Port A, Bit 3 – ADC3/T0/PCINT3
ADC3: Analog to digital converter, channel 3.
T0: Timer/counter0 counter source.
PCINT3: Pin change interrupt source 3. The PA3 pin can serve as an external interrupt source for pin change interrupt 0.
• Port A, Bit 4 – ADC4/USCK/SCL/T1/PCINT4
ADC4: Analog to digital converter, channel 4.
USCK: Three-wire mode universal serial interface clock.
SCL: Two-wire mode serial clock for USI two-wire mode.
T1: Timer/Counter1 counter source.
PCINT4: Pin change interrupt source 4. The PA4 pin can serve as an external interrupt source for pin change interrupt 0.
• Port A, Bit 5 – ADC5/DO/OC1B/PCINT5
ADC5: Analog to digital converter, channel 5.
DO: Data output in USI three-wire mode. Data output (DO) overrides PORTA5 value and it is driven to the port when the
data direction bit DDA5 is set (one). However the PORTA5 bit still controls the pullup, enabling pullup if direction is input and
PORTA5 is set(one).
OC1B: Output compare match output: The PA5 pin can serve as an external output for the Timer/Counter1 compare Match
B. The PA5 pin has to be configured as an output (DDA5 set (one)) to serve this function. The OC1B pin is also the output
pin for the PWM mode timer function.
PCINT5: Pin change interrupt source 5. The PA5 pin can serve as an external interrupt source for pin change interrupt 0.
• Port A, Bit 6 – ADC6/DI/SDA/OC1A/PCINT6
ADC6: Analog to digital converter, channel 6.
SDA: Two-wire mode serial interface data.
DI: Data input in USI three-wire mode. USI three-wire mode does not override normal port functions, so pin must be
configure as an input for DI function.
OC1A, Output compare match output: The PA6 pin can serve as an external output for the Timer/Counter1 compare match
A. The PA6 pin has to be configured as an output (DDA6 set (one)) to serve this function. The OC1A pin is also the output
pin for the PWM mode timer function.
PCINT6: Pin change interrupt source 6. The PA6 pin can serve as an external interrupt source for pin change interrupt 0.
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• Port A, Bit 7 – ADC7/OC0B/ICP1/PCINT7
ADC7: Analog to digital converter, channel 7.
OC1B, output compare match output: The PA7 pin can serve as an external output for the Timer/Counter1 compare match
B. The PA7 pin has to be configured as an output (DDA7 set (one)) to serve this function. The OC1B pin is also the output
pin for the PWM mode timer function.
ICP1, input capture Pin: The PA7 pin can act as an input capture pin for Timer/Counter1.
PCINT7: Pin change interrupt source 7. The PA7 pin can serve as an external interrupt source for pin change interrupt 0.
Table 19-4 to Table 19-6 on page 74 relate the alternate functions of port A to the overriding signals
shown in Figure 19-5 on page 69.
Table 19-4. Overriding Signals for Alternate Functions in PA7..PA5
Signal
Name PA7/ADC7/OC0B/ICP1/ PCINT7 PA6/ADC6/DI/SDA/OC1A/ PCINT6 PA5/ADC5/DO/OC1B/ PCINT5
PUOE 000
PUOV 000
DDOE 0USIWM1 0
DDOV 0(SDA + PORTA6) × DDRA6 0
PVOE OC0B enable (USIWM1× DDA6) + OC1A enable (USIWM1 × USIWM0) + OC1B
enable
PVOV OC0B (USIWM1× DDA6) × OC1A USIWM1 × USIWM0 × DO +
(~USIWM1 × USIWM0) × OC1B}
PTOE 000
DIEOE PCINT7 × PCIE0 + ADC7D USISIE + (PCINT6× PCIE0) +
ADC6D PCINT5 × PCIE + ADC5D
DIEOV PCINT7 × PCIE0 USISIE + PCINT7 × PCIE0 PCINT5 × PCIE
DI PCINT7/ICP1 Input DI/SDA/PCINT6 Input PCINT5 Input
AIO ADC7 Input ADC6 Input ADC5 Input
Table 19-5. Overriding Signals for Alternate Functions in PA4..PA2
Signal
Name PA4/ADC4/USCK/SCL/T1/PCINT4 PA3/ADC3/T0/PCINT3 PA2/ADC2/AIN1/PCINT2
PUOE 0 0 0
PUOV 0 0 0
DDOE USIWM1 0 0
DDOV USI_SCL_HOLD + PORTA4) ×
ADC4D 0 0
PVOE USIWM1 × ADC4D 0 0
PVOV 0 0 0
PTOE USI_PTOE 0 0
DIEOE USISIE + (PCINT4 × PCIE0) +
ADC4D (PCINT3 × PCIE0) + ADC3D PCINT2 × PCIE + ADC2D
DIEOV USISIE +
(PCINT4 × PCIE0) PCINT3 × PCIE0 PCINT3 × PCIE0
DI USCK/SCL/T1/PCINT4 input PCINT1 Input PCINT0 Input
AIO ADC4 Input ADC3 Input ADC2/Analog Comparator Negative
Input
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19.3.2 Alternate Functions of Port B
The port B pins with alternate function are shown in Table 19-7.
• Port B, Bit 0 – XTAL1/PCINT8
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. When using internal calibrated RC oscillator as a chip clock source, PB0
serves as an ordinary I/O pin.
PCINT8: Pin change interrupt source 8. The PB0 pin can serve as an external interrupt source for pin change interrupt 1.
Table 19-6. Overriding Signals for Alternate Functions in PA1..PA0
Signal
Name
PA1/ADC1/AIN0/PCINT1
PA0/ADC0/AREF/PCINT0
PUOE 0RESET ×
(REFS1 × REFS0 + REFS1× REFS0)
PUOV 0 0
DDOE 0RESET ×
(REFS1× REFS0 + REFS1 × REFS0)
DDOV 0 0
PVOE 0RESET ×
(REFS1 × REFS0 + REFS1 × REFS0)
PVOV 0 0
PTOE 0 0
DIEOE PCINT1 × PCIE0 + ADC1D PCINT0 × PCIE0 + ADC0D
DIEOV PCINT1 × PCIE0 PCINT0 × PCIE0
DI PCINT1 Input PCINT0 Input
AIO ADC1/Analog Comparator Positive Input ADC1 Input
Analog reference
Table 19-7. Port B Pins Alternate Functions
Port Pin Alternate Function
PB0 XTAL1: Crystal oscillator Input.
PCINT8: Pin change interrupt 1 source 8.
PB1 XTAL2: Crystal oscillator Output.
PCINT9: Pin change interrupt 1 source 9.
PB2
INT0: External interrupt 0 input.
OC0A: Timer/Counter0 compare match A output.
CKOUT: System clock output.
PCINT10: Pin change interrupt 1 source 10.
PB3
RESET: Reset pin.
dW: debugWire I/O.
PCINT11: Pin change interrupt 1 source 11.
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• Port B, Bit 1 – XTAL2/PCINT9
XTAL2: Chip clock oscillator pin 2. Used as clock pin for all chip clock sources except internal calibrated RC oscillator and
external clock. When used as a clock pin, the pin can not be used as an I/O pin. When using internal calibrated RC oscillator
or external clock as a chip clock sources, PB1 serves as an ordinary I/O pin.
PCINT9: Pin change interrupt source 9. The PB1 pin can serve as an external interrupt source for pin change interrupt 1.
• Port B, Bit 2 – INT0/OC0A/CKOUT/PCINT10
INT0: External interrupt request 0.
OC0A: output compare match output: The PB2 pin can serve as an external output for the Timer/Counter0 compare match
A. The PB2 pin has to be configured as an output (DDB2 set (one)) to serve this function. The OC0A pin is also the output
pin for the PWM mode timer function.
CKOUT - system clock output: The system clock can be output on the PB2 pin. The system clock will be output if the CKOUT
fuse is programmed, regardless of the PORTB2 and DDB2 settings. It will also be output during reset.
PCINT10: Pin change interrupt source 10. The PB2 pin can serve as an external interrupt source for pin change interrupt 1.
• Port B, Bit 3 – RESET/dW/PCINT11
RESET: External Reset input is active low and enabled by unprogramming (“1”) the RSTDISBL Fuse. Pullup is activated and
output driver and digital input are deactivated when the pin is used as the RESET pin.
dW: 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.
PCINT11: Pin change interrupt source 11. The PB3 pin can serve as an external interrupt source for pin change interrupt 1.
Table 19-8 and Table 19-9 relate the alternate functions of port B to the overriding signals shown in Figure 19-5 on page 69.
Table 19-8. Overriding Signals for Alternate Functions in PB3..PB2
Signal
Name
PB3/RESET/dW/
PCINT11 PB2/INT0/OC0A/CKOUT/PCINT10
PUOE RSTDISBL(1)+ DEBUGWIRE_ENABLE(2) CKOUT
PUOV 1 0
DDOE RSTDISBL(1) + DEBUGWIRE_ENABLE(2) CKOUT
DDOV DEBUGWIRE_ENABLE(2) × debugWire Transmit 1'b1
PVOE RSTDISBL(1) + DEBUGWIRE_ENABLE(2) CKOUT + OC0A enable
PVOV 0CKOUT × System Clock + CKOUT × OC0A
PTOE 0 0
DIEOE RSTDISBL(1) + DEBUGWIRE_ENABLE(2) +
PCINT11 × PCIE1 PCINT10 ×PCIE1 + INT0
DIEOV DEBUGWIRE_ENABLE(3) +
(RSTDISBL(1) × PCINT11 × PCIE1) PCINT10 ×PCIE1 + INT0
DI dW/PCINT11 Input INT0/PCINT10 Input
AIO
Note: 1. RSTDISBL is 1 when the fuse is “0” (programmed).
2. DebugWIRE is enabled wheb DWEN fuse is programmed and lock bits are unprogrammed.
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19.4 Register Description
19.4.1 MCUCR – MCU Control Register
• Bits 7, 2– Res: Reserved Bits
These bits are reserved bits in the Atmel® ATtiny24/44/84 and will always read as zero.
• Bit 6 – 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 19.2.1 “Configuring the Pin” on page 65 for more
details about this feature.
19.4.2 PORTA – Port A Data Register
Table 19-9. Overriding Signals for Alternate Functions in PB1..PB0
Signal
Name PB1/XTAL2/PCINT9 PB0/XTAL1/PCINT8
PUOE EXT_OSC(1) EXT_CLOCK(2)+ EXT_OSC(1)
PUOV 0 0
DDOE EXT_OSC(1) EXT_CLOCK(2) + EXT_OSC(1)
DDOV 0 0
PVOE EXT_OSC(1) EXT_CLOK(2) + EXT_OSC(1)
PVOV 0 0
PTOE 0 0
DIEOE EXT_OSC (1)+
PCINT9 × PCIE1
EXT_CLOCK(2) + EXT_OSC(1) +
(PCINT8 × PCIE1)
DIEOV EXT_OSC(1) × PCINT9 × PCIE1 ( EXT_CLOCK(2) × PWR_DOWN) +
(EXT_CLOCK(2) × EXT_OSC(1) × PCINT8 • PCIE1)
DI PCINT9 Input CLOCK/PCINT8 Input
AIO XTAL2 XTAL1
Note: 1. EXT_OSC = crystal oscillator or low frequency crystal oscillator is selected as system clock.
2. EXT_CLOCK = external clock is selected as system clock.
Bit 7 6 5 4 3 2 1 0
–PUD
SE SM1 SM0 – ISC01 ISC00 MCUCR
Read/Write R R/W R/W R/W R/W R R R
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
0x1B (0x3B) PORTA7 PORTA6 PORTA5 PORTA4 PORTA3 PORTA2 PORTA1 PORTA0 PORTA
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
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19.4.3 DDRA – Port A Data Direction Register
19.4.4 PINA – Port A Input Pins Address
19.4.5 PORTB – Port B Data Register
19.4.6 DDRB – Port B Data Direction Register
19.4.7 PINB – Port BInput Pins Address
Bit 76543210
0x1A (0x3A) DDA7 DDA6 DDA5 DDA4 DDA3 DDA2 DDA1 DDA0 DDRB
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x19 (0x39) PINA7 PINA6 PINA5 PINA4 PINA3 PINA2 PINA1 PINA0 PINB
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 N/A N/A N/A N/A N/A N/A
Bit 76543210
0x18 (0x38) – – PORTB3 PORTB2 PORTB1 PORTB0 PORTB
Read/Write R R R R R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x17 (0x37) – – DDB3 DDB2 DDB1 DDB0 DDRB
Read/Write R R R R R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x16 (0x36) – – PINB3 PINB2 PINB1 PINB0 PINB
Read/Write R R R R R/W R/W R/W R/W
Initial Value 0 0 N/A N/A N/A N/A N/A N/A
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20. 8-bit Timer/Counter0 with PWM
20.1 Features
●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)
20.2 Overview
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.
A simplified block diagram of the 8-bit timer/counter is shown in Figure 20-1. For the actual placement of I/O pins. CPU
accessible I/O registers, including I/O bits and I/O pins, are shown in bold. The device-specific I/O register and bit locations
are listed in the Section 20.9 “Register Description” on page 88.
Figure 20-1. 8-bit Timer/Counter Block Diagram
Control Logic
TCNTn
Timer/Counter
Count
Clear
Direction
clkTn
OCRnA
OCRnB
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 OCnB
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20.2.1 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) is 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 20.5 “Output Compare Unit” on page 81 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.
20.2.2 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 20-1 are also used extensively throughout the document.
20.3 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 (CS02:0) bits located in the timer/counter Control register (TCCR0B). For details
on clock sources and prescaler, see Section 22. “Timer/Counter Prescaler” on page 120.
Table 20-1. 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.
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20.4 Counter Unit
The main part of the 8-bit timer/counter is the programmable bi-directional counter unit. Figure 20-2 shows a block diagram
of the counter and its surroundings.
Figure 20-2. Counter Unit Block Diagram
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 output
OC0A. For more details about advanced counting sequences and waveform generation,
see Section 20.7 “Modes of Operation” on page 83.
The timer/counter overflow flag (TOV0) is set according to the mode of operation selected by the WGM01:0 bits. TOV0 can
be used for generating a CPU interrupt.
topbottom
TOVn
(Int. Req.)
DATA BUS
Control LogicTCNTn clkTn
clear
count
direction
Edge
Detector
(from Prescaler)
Clock Select
Tn
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20.5 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 20.7 “Modes of Operation” on page 83.
Figure 20-3 shows a block diagram of the output compare unit.
Figure 20-3. Output Compare Unit, Block Diagram
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.
20.5.1 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 (0x) 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).
20.5.2 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.
OCFnx (Int. Req.)
= (8-bit Comparator)
OCRnx
Waveform Generator
TCNTn
OCnx
top
bottom
FOCn
WGMn1:0 COMnx1:0
DATA BUS
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20.5.3 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 down-counting.
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 (0x) 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.
20.6 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 20-4 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”.
Figure 20-4. 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 20.9 “Register Description” on page 88
DATA BUS
0
1
QD
COMnx1
COMnx0
FOCn
OCnx
Waveform
Generator
QD
PORT
QD
DDR
OCnx
Pin
clkI/O
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20.6.1 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 20-2 on page 88. For fast PWM mode, refer to
Table 20-3 on page 89, and for phase correct PWM refer to Table 20-4 on page 89.
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 0x strobe bits.
20.7 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 20.7 “Modes of Operation” on
page 83).
For detailed timing information refer to Figure 20-8 on page 87, Figure 20-9 on page 87, Figure 20-10 on page 87
and Figure 20-11 on page 88 in Section 20.8 “Timer/Counter Timing Diagrams” on page 87.
20.7.1 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.
20.7.2 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 20-5. The counter value (TCNT0) increases until a compare match
occurs between TCNT0 and OCR0A, and then counter (TCNT0) is cleared.
Figure 20-5. CTC Mode, Timing Diagram
12
TCNTn
(COMnx1:0 = 1)
OCn
(Toggle)
Period 3
OCnx Interrupt Flag Set
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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 0=f
clk_I/O/2 when OCR0A is set to zero (0x00). 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 TOV0 flag is set in the same timer clock cycle that the counter counts
from MAX to 0×00.
20.7.3 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 0×FF 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 20-6. 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 20-6. Fast PWM Mode, Timing Diagram
fOCnx
fclk_I/O
2N1OCRnx+()⋅⋅
-------------------------------------------------
=
1234567
TCNTn
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCnx
OCnx
Period
OCRnx Update and
TOVn Interrupt Flag Set
OCRnx Interrupt
Flag Set
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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 allowes the AC0A pin to toggle on compare matches if the WGM02 bit is set. This option
is not available for the OC0B pin (See Table 20-3 on page 89). 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).
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 0 = 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.
20.7.4 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 down-counting. 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 20-7 on page 86. 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.
fOCnxPWM
fclk_I/O
N256⋅
-----------------
=
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Figure 20-7. Phase Correct PWM Mode, Timing Diagram
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 20-4 on page 89). 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 20-7 OCn has a transition from high to low even though there is no compare match.
The point of this transition is to guaratee symmetry around BOTTOM. There are two cases that give a transition without
compare match.
●OCR0A changes its value from MAX, like in Figure 20-7. 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 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 OCR0A, and for that reason misses the compare match
and hence the OCn change that would have happened on the way up.
123
TCNTn
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCnx
OCnx
Period
TOVn Interrupt
Flag Set
OCRnx Update
OCnx Interrupt
Flag Set
fOCnxPCPWM
fclk_I/O
N510⋅
-----------------
=
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20.8 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 20-8 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 20-8. Timer/Counter Timing Diagram, no Prescaling
Figure 20-9 shows the same timing data, but with the prescaler enabled.
Figure 20-9. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
Figure 20-10 shows the setting of OCF0B in all modes and OCF0A in all modes except CTC mode and PWM mode, where
OCR0A is TOP.
Figure 20-10.Timer/Counter Timing Diagram, Setting of OCF0x, with Prescaler (fclk_I/O/8)
MAX - 1
clkI/O
(clkI/O/1)
TCNTn
TOVn
clkTn
MAX BOTTOM BOTTOM + 1
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
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Figure 20-11 shows the setting of OCF0A and the clearing of TCNT0 in CTC mode and fast PWM mode where OCR0A is
TOP.
Figure 20-11.Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with Prescaler (fclk_I/O/8)
20.9 Register Description
20.9.1 TCCR0A – Timer/Counter Control Register A
• 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 20-2 shows the COM0A1:0 bit functionality when the WGM02:0 bits are set to a normal or CTC mode (non-PWM).
TOP - 1
clkI/O
(clkI/O/8)
TCNTn
(CTC)
OCRnx
OCFnx
clkTn
TOP BOTTOM
TOP
BOTTOM + 1
Bit 7 6 5 4 3 2 1 0
0x30 (0x50) COM0A1 COM0A0 COM0B1 COM0B0 – – 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 20-2. Compare Output Mode, non-PWM Mode
COM01 COM00 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
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Table 20-3 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to fast PWM mode.
Table 20-4 shows the COM0A1:0 bit functionality when the WGM02:0 bits are set to phase correct PWM mode.
• 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 20-2 on page 88 shows the COM0A1:0 bit functionality when the WGM02:0 bits are set to a normal or CTC mode
(non-PWM).
Table 20-3. Compare Output Mode, Fast PWM Mode(1)
COM01 COM00 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 BOTTOM
(non-inverting mode)
1 1 Set OC0A on Compare Match, clear OC0A at BOTTOM
(inverting mode)
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 BOTTOM. See Section 20.7.3 “Fast PWM Mode” on page 84 for more
details.
Table 20-4. 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 20.7.4 “Phase Correct PWM Mode” on page 85 for
more details.
Table 20-5. Compare Output Mode, non-PWM Mode
COM01 COM00 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
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Table 20-3 on page 89 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to fast PWM mode.
Table 20-4 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® ATtiny24/44/84 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 20-8. 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 20.7 “Modes of Operation” on page 83).
Table 20-6. Compare Output Mode, Fast PWM Mode(1)
COM01 COM00 Description
0 0 Normal port operation, OC0B disconnected.
0 1 Reserved
1 0 Clear OC0B on compare match, set OC0B at BOTTOM
(non-inverting mode)
1 1 Set OC0B on compare match, clear OC0B at BOTTOM
(inverting mode)
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 BOTTOM. See Section 20.7.3 “Fast PWM Mode” on page 84 for more
details.
Table 20-7. Compare Output Mode, Phase Correct PWM Mode(1)
COM0A1 COM0A0 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 20.7.4 “Phase Correct PWM Mode” on page 85 for
more details.
Table 20-8. Waveform Generation Mode Bit Description
Mode WGM2 WGM1 WGM0
Timer/Counter Mode of
Operation TOP
Update of
OCRx at
TOV Flag
Set on(1)
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 BOTTOM 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 BOTTOM TOP
Note: 1. MAX = 0xFF
BOTTOM = 0x00
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20.9.2 TCCR0B – Timer/Counter Control Register B
• 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® ATtiny24/44/84 and will always read as zero.
• Bit 3 – WGM02: Waveform Generation Mode
See the description in the Section 20.9.1 “TCCR0A – Timer/Counter Control Register A” on page 88.
• Bits 2:0 – CS02:0: Clock Select
The three clock select bits select the clock source to be used by the timer/counter.
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.
Bit 7 6 5 4 3 2 1 0
0x33 (0x53) FOC0A FOC0B – – WGM02 CS02 CS01 CS00 TCCR0B
Read/Write W W R R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 20-9. Clock Select Bit Description
CS02 CS01 CS00 Description
0 0 0 No clock source (Timer/Counter stopped)
0 0 1 clkI/O/(No prescaling)
0 1 0 clkI/O/8 (from prescaler)
0 1 1 clkI/O/64 (from prescaler)
1 0 0 clkI/O/256 (from prescaler)
1 0 1 clkI/O/1024 (from prescaler)
1 1 0 External clock source on T0 pin. Clock on falling edge.
1 1 1 External clock source on T0 pin. Clock on rising edge.
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20.9.3 TCNT0 – Timer/Counter Register
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.
20.9.4 OCR0A – Output Compare Register A
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.
20.9.5 OCR0B – Output Compare Register B
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.
20.9.6 TIMSK0 – Timer/Counter 0 Interrupt Mask Register
• Bits 7..3 – Res: Reserved Bits
These bits are reserved bits in the Atmel® ATtiny24/44/84 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 76543210
0x32 (0x52) 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
0x36 (0x56) 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
0x3C (0x5C) OCR0B[7:0] OCR0B
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x39 (0x59) –––––OCIE0BOCIE0ATOIE0TIMSK0
Read/WriteRRRRRR/WR/WR/W
Initial Value00000000
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• 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 – TIFR0.
20.9.7 TIFR0 – Timer/Counter 0 Interrupt Flag Register
• Bits 7..3 – Res: Reserved Bits
These bits are reserved bits in the Atmel® ATtiny24/44/84 and will always read as zero.
• Bit 2– OCF0B: Output Compare Flag 0 B
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: Output Compare Flag 0 A
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. See Table 20-8 on page 90.
Bit 76543210
0x38 (0x58) – – – – – OCF0B OCF0A TOV0 TIFR0
Read/Write R R R R R R/W R/W R/W
Initial Value00000000
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21. 16-bit Timer/Counter1
21.1 Features
●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)
●Variable PWM period
●Frequency generator
●External event counter
●Four independent interrupt sources (TOV1, OCF1A, OCF1B, and ICF1)
21.2 Overview
The 16-bit timer/counter unit allows accurate program execution timing (event management), wave generation, and signal
timing measurement.
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 21-1 on page 95. For the actual placement of I/O
pins. CPU accessible I/O registers, including I/O bits and I/O pins, are shown in bold. The device-specific I/O register and bit
locations are listed in the Section 21.11 “Register Description” on page 114.
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Figure 21-1. 16-bit Timer/Counter Block Diagram
21.2.1 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
Section 21.3 “Accessing 16-bit Registers” on page 96. 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 (TIFR). All interrupts are individually masked with the timer interrupt mask register (TIMSK). TIFR
and TIMSK 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 21.7 “Output Compare Units” on page 102. 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 24. “Analog Comparator” on page 133). The input capture
unit includes a digital filtering unit (noise canceler) for reducing the chance of capturing noise spikes.
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
Values
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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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.
21.2.2 Definitions
The following definitions are used extensively throughout the section:
21.2.3 Compatibility
The 16-bit timer/counter has been updated and improved from previous versions of the 16-bit AVR® timer/counter. This
16-bit timer/counter is fully compatible with the earlier version regarding:
●All 16-bit timer/counter related I/O register address locations, including timer interrupt registers.
●Bit locations inside all 16-bit timer/counter registers, including timer interrupt registers.
●Interrupt vectors.
The following control bits have changed name, but have same functionality and register location:
●PWM10 is changed to WGM10.
●PWM11 is changed to WGM11.
●CTC1 is changed to WGM12.
The following bits are added to the 16-bit timer/counter control registers:
●1A and 1B are added to TCCR1A.
●WGM13 is added to TCCR1B.
The 16-bit timer/counter has improvements that will affect the compatibility in some special cases.
21.3 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 21-1. 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. See Section 11. “About Code Examples” on page 20.
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.
Notes: 1. See Section 11. “About Code Examples” on page 20.
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. See Section 11. “About Code Examples” on page 20.
The assembly code example requires that the r17:r16 register pair contains the value to be written to TCNT1.
21.3.1 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.
21.4 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 22. “Timer/Counter Prescaler” on page 120.
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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21.5 Counter Unit
The main part of the 16-bit timer/counter is the programmable 16-bit bi-directional counter unit. Figure 21-2 on page 100
shows a block diagram of the counter and its surroundings.
Figure 21-2. 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 21.9 “Modes of Operation” on page 105.
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.
BOTTOMTOP
TOVn
(Int. Req.)
DATA BUS (8-bit)
Control Logic
TCNTnH (8-bit)
TCNTn (16-bit Counter)
TCNTnL (8-bit)
TEMP (8-bit)
clkTn
Clear
Count
Direction
Edge
Detector
(from Prescaler)
Clock Select
Tn
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21.6 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 21-3. 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.
Figure 21-3. 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 21.3 “Accessing 16-bit Registers” on page 96.
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
ICNCACIC*ACO*
WRITE
+
-
ICES
ICPn
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21.6.1 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 (Figure 22-1 on page 120). 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.
21.6.2 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.
21.6.3 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).
21.7 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
(Section 21.9 “Modes of Operation” on page 105).
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.
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Figure 21-4 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.
Figure 21-4. 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 21.3 “Accessing 16-bit Registers” on page 96.
21.7.1 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 (1x) 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).
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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21.7.2 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.
21.7.3 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 (1x) 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.
21.8 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 21-5 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 21-5. 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. See Table 21-2 on page 114, Table 21-3 on page 114 and Table 21-4 on page 115 for details.
DATA BUS
0
1
QD
COMnx1
COMnx0
FOCn
OCnx
Waveform
Generator
QD
PORT
QD
DDR
OCnx
Pin
clkI/O
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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 21.11 “Register Description” on page 114. The COM1x1:0 bits have no effect on the input capture unit.
21.8.1 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 21-2 on page 114. For fast PWM mode refer to
Table 21-3 on page 114, and for phase correct and phase and frequency correct PWM refer to Table 21-4 on page 115.
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 1x strobe bits.
21.9 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
(Section 21.8 “Compare Match Output Unit” on page 104)
For detailed timing information refer to Section 21.10 “Timer/Counter Timing Diagrams” on page 112.
21.9.1 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.
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21.9.2 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 21-6. The counter value (TCNT1) increases until a compare match
occurs with either OCR1A or ICR1, and then counter (TCNT1) is cleared.
Figure 21-6. CTC Mode, Timing Diagram
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 1A = 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.
12
TCNTn
(COMnA1:0 = 1)
OCnA
(Toggle)
Period 3
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
4
fOCnA
fclk_I/O
2N1OCRnA+()⋅⋅
--------------------------------------------------
=
107
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21.9.3 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 cleared on the compare match between TCNT1 and OCR1x, and set at BOTTOM. In inverting compare output
mode 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 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 21-7 on page 107. 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.
Figure 21-7. 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.
RFPWM
TOP 1+()log
2()log
----------------------------------
=
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)
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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 21-3 on page 114). 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.)
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). The waveform generated will have a maximum frequency of 1A = 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.
21.9.4 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:
fOCnxPWM
fclk_I/O
N1TOP+()⋅
----------------------------------
=
RPCPWM
TOP 1+()log
2()log
----------------------------------
=
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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 21-8 on page 109. 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 21-8. Phase Correct PWM Mode, Timing Diagram
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.
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)
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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 21-8 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 (See Table 21-4 on page 115). 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.
21.9.5 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 21-8 on page 109 and Figure 21-9 on page 111).
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
TOP 1+()log
2()log
----------------------------------
=
111
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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 21-9. 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 21-9. 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 21-9 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.
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)
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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 21-4 on page 115). 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).
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.
21.10 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 21-10 shows a timing diagram for the setting
of OCF1x.
Figure 21-10.Timer/Counter Timing Diagram, Setting of OCF1x, no Prescaling
Figure 21-11 shows the same timing data, but with the prescaler enabled.
Figure 21-11.Timer/Counter Timing Diagram, Setting of OCF1x, with Prescaler (fclk_I/O/8)
fOCnxPFCPWM
fclk_I/O
2NTOP⋅⋅
----------------------------
=
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 21-12 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 21-12.Timer/Counter Timing Diagram, no Prescaling
Figure 21-13 shows the same timing data, but with the prescaler enabled.
Figure 21-13.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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21.11 Register Description
21.11.1 TCCR1A – Timer/Counter1 Control Register A
• 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 21-2 shows the COM1x1:0 bit functionality when the WGM13:0 bits are set to a normal or a CTC mode (non-
PWM).
Table 21-3 shows the COM1x1:0 bit functionality when the WGM13:0 bits are set to the fast PWM mode.
Bit 76543210
0x2F (0x4F) COM1A1 COM1A0 COM1B1 COM1B0 – – WGM11 WGM10 TCCR1A
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 21-2. 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 21-3. Compare Output Mode, Fast PWM(1)
COM1A1/COM1B1 COM1A0/COM1B0 Description
0 0 Normal port operation, OC1A/OC1B disconnected.
0 1 WGM13=0: Normal port operation, OC1A/OC1B disconnected.
WGM13=1: Toggle OC1A on compare match, OC1B reserved.
1 0 Clear OC1A/OC1B on compare match, set OC1A/OC1B at
BOTTOM (non-inverting mode)
1 1 Set OC1A/OC1B on compare Mmtch, clear OC1A/OC1B at
BOTTOM (inverting mode)
Note: 1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is set. In this case the com-
pare match is ignored, but the set or clear is done at BOTTOM. Section 21.9.3 “Fast PWM Mode” on page 107
for more details.
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Table 21-4 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 21-5 on page 115.
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. (Section 21.9 “Modes of Operation” on page 105).
Table 21-4. 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: Normal port operation, OC1A/OC1B disconnected.
WGM13=1: Toggle OC1A on compare match, OC1B reserved.
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.
Notes: 1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is set.
Section 21.9.4 “Phase Correct PWM Mode” on page 108 for more details.
Table 21-5. 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
0 0 0 0 0 Normal 0xFFFF Immediate MAX
1 0 0 0 1 PWM, phase correct, 8-bit 0x00FF TOP BOTTOM
2 0 0 1 0 PWM, phase correct, 9-bit 0x01FF TOP BOTTOM
3 0 0 1 1 PWM, phase correct, 10-bit 0x03FF TOP BOTTOM
4 0 1 0 0 CTC OCR1A Immediate MAX
5 0 1 0 1 Fast PWM, 8-bit 0x00FF BOTTOM TOP
6 0 1 1 0 Fast PWM, 9-bit 0x01FF BOTTOM TOP
7 0 1 1 1 Fast PWM, 10-bit 0x03FF BOTTOM TOP
8 1 0 0 0 PWM, phase and frequency
correct ICR1 BOTTOM BOTTOM
9 1 0 0 1 PWM, phase and frequency
correct OCR1A BOTTOM BOTTOM
10 1 0 1 0 PWM, phase correct ICR1 TOP BOTTOM
11 1 0 1 1 PWM, phase correct OCR1A TOP BOTTOM
12 1 1 0 0 CTC ICR1 Immediate MAX
13 1 1 0 1 (Reserved) – – –
14 1 1 1 0 Fast PWM ICR1 BOTTOM TOP
15 1 1 1 1 Fast PWM OCR1A BOTTOM TOP
Note: 1. The CTC1 and PWM11:0 bit definition names are obsolete. Use the WGM12:0 definitions. However, the func-
tionality and location of these bits are compatible with previous versions of the timer.
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21.11.2 TCCR1B – Timer/Counter1 Control Register B
• 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 21-10 on page 112
and Figure 21-11 on page 112.
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
0x2E (0x4E) 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 21-6. 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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21.11.3 TCCR1C – Timer/Counter1 Control Register C
• 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.
• Bit 5..0 – Reserved Bit
This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be written to zero when the
register is written.
21.11.4 TCNT1H and TCNT1L – Timer/Counter1
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 21.3 “Accessing 16-bit Registers” on page 96.
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.
21.11.5 OCR1AH and OCR1AL – Output Compare Register 1 A
Bit 7654 3210
0x22 (0x42) FOC1AFOC1B–– ––––TCCR1C
Read/Write W W R R R R R R
Initial Value00000000
Bit 76543210
0x2D (0x4D) TCNT1[15:8] TCNT1H
0x2C (0x4C) 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
0x2B (0x4B) OCR1A[15:8] OCR1AH
0x2A (0x4A) OCR1A[7:0] OCR1AL
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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21.11.6 OCR1BH and OCR1BL – Output Compare Register 1 B
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 21.3 “Accessing 16-bit Registers” on page 96.
21.11.7 ICR1H and ICR1L – Input Capture Register 1
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. Section 21.3 “Accessing 16-bit Registers” on page 96.
21.11.8 TIMSK1 – Timer/Counter Interrupt Mask Register 1
• Bit 7,6,4,3 – Reserved Bit
This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be written to zero when the
register is written.
• 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/counter input
capture interrupt is enabled. The
corresponding interrupt vector (See “Interrupts” on page 66.) is executed when the ICF1 flag, located in TIFR1, is set.
• 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 17. “Interrupts” on page 59) 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 17. “Interrupts” on page 59) is
executed when the OCF1A flag, located in TIFR1, is set.
Bit 76543210
0x29 (0x49) OCR1B[15:8] OCR1BH
0x28 (0x48) OCR1B[7:0] OCR1BL
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x25 (0x45) ICR1[15:8] ICR1H
0x24 (0x44) 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 7 6 5 4 3 2 1 0
0x0C (0x2C) – – ICIE1 – – OCIE1B OCIE1A TOIE1 TIMSK1
Read/Write R R R/W R R R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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• 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 17. “Interrupts” on page 59) is executed when
the TOV1 flag, located in TIFR1, is set.
21.11.9 TIFR1 – Timer/Counter Interrupt Flag Register 1
• Bit 7,6,4,3 – Reserved Bit
This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be written to zero when the
register is written.
• 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 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 (1B) 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 (1A) 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. See Table 21-5 on page 115 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.
Bit 765432 1 0
0x0B (0x2B) – – ICIF1 – – OCF1B OCF1A TOV1 TIFR1
Read/Write R R R/W R R R/W R/W R/W
Initial Value000000 0 0
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22. Timer/Counter Prescaler
Timer/Counter 0, and 1 share the same prescaler module, but the timer/counters can have different prescaler settings. The
description below applies to all timer/counters. Tn is used as a general name, n = 0, 1.
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.
22.1 Prscaler eReset
The prescaler is free running, i.e., operates independently of the clock select logic of the timer/counter, and it is shared by
the timer/counter Tn. 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.
22.2 External Clock Source
An external clock source applied to the Tn pin can be used as timer/counter clock (clkTn). The Tn 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 22-1 shows a functional equivalent block diagram of the Tn 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 clkT0 pulse for each positive (CSn2:0 = 7) or negative (CSn2:0 = 6) edge it detects.
Figure 22-1. 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 Tn pin to the counter is updated.
Enabling and disabling of the clock input must be done when Tn has been stable for at least one system clock cycle,
otherwise it is a risk that a false timer/counter clock pulse is generated.
Tn
Synchronization Edge Detector
Tn_sync
(to Clock
Select Logic)
Q
LE
D QD QD
clkI/O
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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.
Figure 22-2. Prescaler for Timer/Counter0
Note: 1. The synchronization logic on the input pins (T0) is shown in Figure 22-1 on page 120.
22.3 Register Description
22.3.1 GTCCR – General Timer/Counter Control Register
• 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
PSR10 bit is kept, hence keeping the prescaler reset signal asserted. This ensures that the timer/counter is halted and can
be configured without the risk of advancing during configuration. When the TSM bit is written to zero, the PSR10 bit is
cleared by hardware, and the timer/counter start counting.
• Bit 0 – PSR10: Prescaler 0 Reset Timer/Counter n
When this bit is one, the timer/counter n prescaler will be reset. This bit is normally cleared immediately by hardware, except
if the TSM bit is set.
Timer/Counter 0 Clock Source
clkI/O
PSR10
T0
10-bit T/C Prescaler
0
CS00
CK/8
CK/64
CK/256
CK/1024
CS01
CS02
Synchronization
Clear
clkT0
Bit 7 6 5 4 3 2 1 0
0x23 (0x43) TSM – – – – – – PSR10 GTCCR
Read/Write R/W R R R R R R R/W
Initial Value 0 0 0 0 0 0 0 0
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23. USI – Universal Serial Interface
23.1 Features
●Two-wire synchronous data transfer (master or slave)
●Three-wire synchronous data transfer (master or slave)
●Data received interrupt
●Wakeup from idle mode
●In two-wire mode: Wake-up from all sleep modes, including power-down mode
●Two-wire start condition detector with interrupt capability
23.2 Overview
The universal serial interface (USI), provides the basic hardware resources needed for serial communication. Combined with
a minimum of control software, the USI allows significantly higher transfer rates and uses less code space than solutions
based on software only. Interrupts are included to minimize the processor load.
A simplified block diagram of the USI is shown in Figure 23-1. For the actual placement of I/O pins. CPU accessible I/O
registers, including I/O bits and I/O pins, are shown in bold. The device-specific I/O register and bit locations are listed in the
Section 23.5 “Register Descriptions” on page 128.
Figure 23-1. Universal Serial Interface, Block Diagram
The 8-bit shift register is directly accessible via the data bus and contains the incoming and outgoing data. The register has
no buffering so the data must be read as quickly as possible to ensure that no data is lost. The most significant bit is
connected to one of two output pins depending of the wire mode configuration. A transparent latch is inserted between the
serial register output and output pin, which delays the change of data output to the opposite clock edge of the data input
sampling. The serial input is always sampled from the data input (DI) pin independent of the configuration.
Q
3
2
1
0
LE
2
USIDR
D
TIM0 COMP
USCK/SCL
Two-wire Clock
Control Unit
CLOCK
HOLD
[1]
Bit0
Bit7
USISIF
USIOIF
USIPF
USIDC
USISR
4-bit Counter
DI/SDA
DO (Output only)
(Input/ Open Drain))
(Input/ Open Drain))
3
2
1
0
1
0
USISIE
USIOIE
USIWM1
USIWM0
USICS1
USICS0
USICLK
USITC
USICR
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The 4-bit counter can be both read and written via the data bus, and can generate an overflow interrupt. Both the serial
register and the counter are clocked simultaneously by the same clock source. This allows the counter to count the number
of bits received or transmitted and generate an interrupt when the transfer is complete. Note that when an external clock
source is selected the counter counts both clock edges. In this case the counter counts the number of edges, and not the
number of bits. The clock can be selected from three different sources: The USCK pin, timer/counter0 compare match or
from software.
The two-wire clock control unit can generate an interrupt when a start condition is detected on the two-wire bus. It can also
generate wait states by holding the clock pin low after a start condition is detected, or after the counter overflows.
23.3 Functional Descriptions
23.3.1 Three-wire Mode
The USI three-wire mode is compliant to the serial peripheral interface (SPI) mode 0 and 1, but does not have the slave
select (SS) pin functionality. However, this feature can be implemented in software if necessary. Pin names used by this
mode are: DI, DO, and USCK.
Figure 23-2. Three-wire Mode Operation, Simplified Diagram
Figure 23-2 shows two USI units operating in three-wire mode, one as master and one as slave. The two shift registers are
interconnected in such way that after eight USCK clocks, the data in each register are interchanged. The same clock also
increments the USI’s 4-bit counter. The counter overflow (interrupt) flag, or USIOIF, can therefore be used to determine
when a transfer is completed. The clock is generated by the master device software by toggling the USCK pin via the PORT
register or by writing a one to the USITC bit in USICR.
Bit7 DI
USCK
USCK
DO
PORTxn
SLAVE
Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
Bit7 DI
DO
MASTER
Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
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Figure 23-3. Three-wire Mode, Timing Diagram
The three-wire mode timing is shown in Figure 23-3. At the top of the figure is a USCK cycle reference. One bit is shifted into
the USI shift register (USIDR) for each of these cycles. The USCK timing is shown for both external clock modes. In external
clock mode 0 (USICS0 = 0), DI is sampled at positive edges, and DO is changed (data register is shifted by one) at negative
edges. external clock mode 1 (USICS0 = 1) uses the opposite edges versus mode 0, i.e., samples data at negative and
changes the output at positive edges. The USI clock modes corresponds to the SPI data mode 0 and 1.
Referring to the timing diagram (Figure 23-3 on page 124), a bus transfer involves the following steps:
1. The slave device and master device sets up its data output and, depending on the protocol used, enables its out-
put driver (mark A and B). The output is set up by writing the data to be transmitted to the serial data register.
Enabling of the output is done by setting the corresponding bit in the port data direction register. Note that point A
and B does not have any specific order, but both must be at least one half USCK cycle before point C where the
data is sampled. This must be done to ensure that the data setup requirement is satisfied. The 4-bit counter is
reset to zero.
2. The master generates a clock pulse by software toggling the USCK line twice (C and D). The bit value on the
slave and master’s data input (DI) pin is sampled by the USI on the first edge (C), and the data output is changed
on the opposite edge (D). The 4-bit counter will count both edges.
3. Step 2 is repeated eight times for a complete register (byte) transfer.
4. After eight clock pulses (i.e., 16 clock edges) the counter will overflow and indicate that the transfer is completed.
The data bytes transferred must now be processed before a new transfer can be initiated. The overflow interrupt
will wake up the processor if it is set to Idle mode. Depending of the protocol used the slave device can now set its
output to high impedance.
23.3.2 SPI Master Operation Example
The following code demonstrates how to use the USI module as a SPI master:
SPITransfer:
out USIDR,r16
ldi r16,(1<<USIOIF)
out USISR,r16
ldi r16,(1<<USIWM0)|(1<<USICS1)|(1<<USICLK)|(1<<USITC)
SPITransfer_loop:
out USICR,r16
in r16, USISR
sbrs r16, USIOIF
rjmp SPITransfer_loop
in r16,USIDR
ret
The code is size optimized using only eight instructions (+ ret). The code example assumes that the DO and USCK pins are
enabled as output in the DDRE register. The value stored in register r16 prior to the function is called is transferred to the
Slave device, and when the transfer is completed the data received from the slave is stored back into the r16 register.
12
6MSB 54321LSB
345678
6MSB
CYCLE
(Reference)
USCK
USCK
54321LSB
A B C D E
DI
DO
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The second and third instructions clears the USI counter overflow flag and the USI counter value. The fourth and fifth
instruction set three-wire mode, positive edge shift register clock, count at USITC strobe, and toggle USCK. The loop is
repeated 16 times.
The following code demonstrates how to use the USI module as a SPI master with maximum speed (fsck = fck/4):
SPITransfer_Fast:
out USIDR,r16
ldi r16,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)
ldi r17,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)|(1<<USICLK)
out USICR,r16 ; MSB
out USICR,r17
out USICR,r16
out USICR,r17
out USICR,r16
out USICR,r17
out USICR,r16
out USICR,r17
out USICR,r16
out USICR,r17
out USICR,r16
out USICR,r17
out USICR,r16
out USICR,r17
out USICR,r16 ; LSB
out USICR,r17
in r16,USIDR
ret
23.3.3 SPI Slave Operation Example
The following code demonstrates how to use the USI module as a SPI slave:
init:
ldi r16,(1<<USIWM0)|(1<<USICS1)
out USICR,r16
...
SlaveSPITransfer:
out USIDR,r16
ldi r16,(1<<USIOIF)
out USISR,r16
SlaveSPITransfer_loop:
in r16, USISR
sbrs r16, USIOIF
rjmp SlaveSPITransfer_loop
in r16,USIDR
ret
The code is size optimized using only eight instructions (+ ret). The code example assumes that the DO is configured as
output and USCK pin is configured as input in the DDR register. The value stored in register r16 prior to the function is called
is transferred to the master device, and when the transfer is completed the data received from the master is stored back into
the r16 register.
Note that the first two instructions is for initialization only and needs only to be executed once.These instructions sets three-
wire mode and positive edge shift register clock. The loop is repeated until the USI counter overflow flag is set.
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23.3.4 Two-wire Mode
The USI two-wire mode is compliant to the inter IC (TWI) bus protocol, but without slew rate limiting on outputs and input
noise filtering. Pin names used by this mode are SCL and SDA.
Figure 23-4. Two-wire Mode Operation, Simplified Diagram
Figure 23-4 shows two USI units operating in two-wire mode, one as master and one as slave. It is only the physical layer
that is shown since the system operation is highly dependent of the communication scheme used. The main differences
between the master and slave operation at this level, is the serial clock generation which is always done by the master, and
only the slave uses the clock control unit. Clock generation must be implemented in software, but the shift operation is done
automatically by both devices. Note that only clocking on negative edge for shifting data is of practical use in this mode. The
slave can insert wait states at start or end of transfer by forcing the SCL clock low. This means that the master must always
check if the SCL line was actually released after it has generated a positive edge.
Since the clock also increments the counter, a counter overflow can be used to indicate that the transfer is completed. The
clock is generated by the master by toggling the USCK pin via the PORT register.
The data direction is not given by the physical layer. A protocol, like the one used by the TWI-bus, must be implemented to
control the data flow.
Figure 23-5. Two-wire Mode, Typical Timing Diagram
Bit7
SDA
SCL
HOLD
SCL
SLAVE
Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
Two-wire
Clock
Control Unit
VCC
Bit7
SDA
SCL
MASTER
Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
PORTxn
1 to 7 8
SADDRESS R/W ACK DATA ACK ACKDATA
1 to 8 9 1 to 8 99
A B C D E F
SDA
SCL
P
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Referring to the timing diagram (Figure 23-5 on page 126), a bus transfer involves the following steps:
1. The a start condition is generated by the master by forcing the SDA low line while the SCL line is high (A). SDA
can be forced low either by writing a zero to bit 7 of the shift register, or by setting the corresponding bit in the
PORT register to zero. Note that the data direction register bit must be set to one for the output to be enabled. The
slave device’s start detector logic (Figure 23-6) detects the start condition and sets the USISIF flag. The flag can
generate an interrupt if necessary.
2. In addition, the start detector will hold the SCL line low after the master has forced an negative edge on this line
(B). This allows the slave to wake up from sleep or complete its other tasks before setting up the shift register to
receive the address. This is done by clearing the start condition flag and reset the counter.
3. The master set the first bit to be transferred and releases the SCL line (C). The slave samples the data and shift it
into the serial register at the positive edge of the SCL clock.
4. After eight bits are transferred containing slave address and data direction (read or write), the slave counter over-
flows and the SCL line is forced low (D). If the slave is not the one the master has addressed, it releases the SCL
line and waits for a new start condition.
5. If the slave is addressed it holds the SDA line low during the acknowledgment cycle before holding the SCL line
low again (i.e., the counter register must be set to 14 before releasing SCL at (D)). Depending of the R/W bit the
master or slave enables its output. If the bit is set, a master read operation is in progress (i.e., the slave drives the
SDA line) The slave can hold the SCL line low after the acknowledge (E).
6. Multiple bytes can now be transmitted, all in same direction, until a stop condition is given by the master (F). Or a
new start condition is given.
If the slave is not able to receive more data it does not acknowledge the data byte it has last received. When the master does
a read operation it must terminate the operation by force the acknowledge bit low after the last byte transmitted.
Figure 23-6. Start Condition Detector, Logic Diagram
23.3.5 Start Condition Detector
The start condition detector is shown in Figure 23-6. The SDA line is delayed (in the range of 50 to 300 ns) to ensure valid
sampling of the SCL line. The start condition detector is only enabled in two-wire mode.
The start condition detector is working asynchronously and can therefore wake up the processor from the power-down sleep
mode. However, the protocol used might have restrictions on the SCL hold time. Therefore, when using this feature in this
case the oscillator start-up time set by the CKSEL fuses
(see Section 14.1 “Clock Systems and their Distribution” on page 37) must also be taken into the consideration. See the
USISIF bit description in Section 23.5.3 “USISR – USI Status Register” on page 129 for further details.
23.3.6 Clock speed considerations
Maximum frequency for SCL and SCK is fCK /4. This is also the maximum data transmit and receive rate in both two- and
three-wire mode. In two-wire slave mode the two-wire clock control unit will hold the SCL low until the slave is ready to
receive more data. This may reduce the actual data rate in two-wire mode.
Q
SDA
SCL
Write (USISIF)
D
CLR
QD
USISIF
CLOCK
HOLD
CLR
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23.4 Alternative USI Usage
When the USI unit is not used for serial communication, it can be set up to do alternative tasks due to its flexible design.
23.4.1 Half-duplex Asynchronous Data Transfer
By utilizing the shift register in three-wire mode, it is possible to implement a more compact and higher performance UART
than by software only.
23.4.2 4-bit Counter
The 4-bit counter can be used as a stand-alone counter with overflow interrupt. Note that if the counter is clocked externally,
both clock edges will generate an increment.
23.4.3 12-bit Timer/Counter
Combining the USI 4-bit counter and timer/counter0 allows them to be used as a 12-bit counter.
23.4.4 Edge Triggered External Interrupt
By setting the counter to maximum value (F) it can function as an additional external interrupt. The overflow flag and interrupt
Enable bit are then used for the external interrupt. This feature is selected by the USICS1 bit.
23.4.5 Software Interrupt
The counter overflow interrupt can be used as a software interrupt triggered by a clock strobe.
23.5 Register Descriptions
23.5.1 USIBR – USI Data Buffer
23.5.2 USIDR – USI Data Register
The USI uses no buffering of the serial register, i.e., when accessing the data register (USIDR) the serial register is
accessed directly. If a serial clock occurs at the same cycle the register is written, the register will contain the value written
and no shift is performed. A (left) shift operation is performed depending of the USICS1..0 bits setting. The shift operation
can be controlled by an external clock edge, by a timer/counter0 compare match, or directly by software using the USICLK
strobe bit. Note that even when no wire mode is selected (USIWM1..0 = 0) both the external data input (DI/SDA) and the
external clock input (USCK/SCL) can still be used by the shift register.
The output pin in use, DO or SDA depending on the wire mode, is connected via the output latch to the most significant bit
(bit 7) of the data register. The output latch is open (transparent) during the first half of a serial clock cycle when an external
clock source is selected (USICS1 = 1), and constantly open when an internal clock source is used (USICS1 = 0). The output
will be changed immediately when a new MSB written as long as the latch is open. The latch ensures that data input is
sampled and data output is changed on opposite clock edges.
Note that the corresponding data direction register to the pin must be set to one for enabling data output from the shift
register.
Bit 7 6 5 4 3 2 1 0
0x10 (0x30) MSB LSB USIBR
Read/Write R R R R R R R R
Initial Value 0 0 0 0 0 0 0 0
Bit 7 6 5 4 3 2 1 0
0x0F (0x2F) MSB LSB USIDR
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
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23.5.3 USISR – USI Status Register
The status register contains interrupt flags, line status flags and the counter value.
• Bit 7 – USISIF: Start Condition Interrupt Flag
When two-wire mode is selected, the USISIF flag is set (to one) when a start condition is detected. When output disable
mode or three-wire mode is selected and (USICSx = 0b11 & USICLK = 0) or (USICS = 0b10 & USICLK = 0), any edge on the
SCK pin sets the flag.
An interrupt will be generated when the flag is set while the USISIE bit in USICR and the global interrupt enable flag are set.
The flag will only be cleared by writing a logical one to the USISIF bit. Clearing this bit will release the start detection hold of
USCL in Two-wire mode.
A start condition interrupt will wakeup the processor from all sleep modes.
• Bit 6 – USIOIF: Counter Overflow Interrupt Flag
This flag is set (one) when the 4-bit counter overflows (i.e., at the transition from 15 to 0). An interrupt will be generated when
the flag is set while the USIOIE bit in USICR and the global interrupt enable flag are set. The flag is cleared if a one is written
to the USIOIF bit or by reading the USIBR register. Clearing this bit will release the counter overflow hold of SCL in two-wire
mode.
A counter overflow interrupt will wakeup the processor from Idle sleep mode.
• Bit 5 – USIPF: Stop Condition Flag
When two-wire mode is selected, the USIPF flag is set (one) when a stop condition is detected. The flag is cleared by writing
a one to this bit. Note that this is not an interrupt flag. This signal is useful when implementing two-wire bus master
arbitration.
• Bit 4 – USIDC: Data Output Collision
This bit is logical one when bit 7 in the shift register differs from the physical pin value. The flag is only valid when two-wire
mode is used. This signal is useful when implementing two-wire bus master arbitration.
• Bits 3..0 – USICNT3..0: Counter Value
These bits reflect the current 4-bit counter value. The 4-bit counter value can directly be read or written by the CPU.
The 4-bit counter increments by one for each clock generated either by the external clock edge detector, by a timer/counter0
compare match, or by software using USICLK or USITC strobe bits. The clock source depends of the setting of the
USICS1..0 bits. For external clock operation a special feature is added that allows the clock to be generated by writing to the
USITC strobe bit. This feature is enabled by write a one to the USICLK bit while setting an external
clock source (USICS1 = 1).
Note that even when no wire mode is selected (USIWM1..0 = 0) the external clock input (USCK/SCL) are can still be used by
the counter.
Bit 7 6 5 4 3 2 1 0
0x0E (0x2E) USISIF USIOIF USIPF USIDC USICNT3 USICNT2 USICNT1 USICNT0 USISR
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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23.5.4 USICR – USI Control Register
The control register includes interrupt enable control, wire mode setting, clock select setting, and clock strobe.
• Bit 7 – USISIE: Start Condition Interrupt Enable
Setting this bit to one enables the start condition detector interrupt. If there is a pending interrupt when the USISIE and the
global interrupt enable flag is set to one, this will immediately be executed. See the USISIF
bit description in Section 23.5.3 “USISR – USI Status Register” on page 129 for further details.
• Bit 6 – USIOIE: Counter Overflow Interrupt Enable
Setting this bit to one enables the counter overflow interrupt. If there is a pending interrupt when the USIOIE and the global
interrupt enable flag is set to one, this will immediately be executed. See the USIOIF
bit description in Section 23.5.3 “USISR – USI Status Register” on page 129 for further details.
• Bit 5..4 – USIWM1..0: Wire Mode
These bits set the type of wire mode to be used. Basically only the function of the outputs are affected by these bits. Data
and clock inputs are not affected by the mode selected and will always have the same function. The counter and shift
register can therefore be clocked externally, and data input sampled, even when outputs are disabled. The relations
between USIWM1..0 and the USI operation is summarized in Table 23-1 on page 131.
Bit 7 6 5 4 3 2 1 0
0x0D (0x2D) USISIE USIOIE USIWM1 USIWM0 USICS1 USICS0 USICLK USITC USICR
Read/Write R/W R/W R/W R/W R/W R/W W W
Initial Value 0 0 0 0 0 0 0 0
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• Bit 3..2 – USICS1..0: Clock Source Select
These bits set the clock source for the shift register and counter. The data output latch ensures that the output is changed at
the opposite edge of the sampling of the data input (DI/SDA) when using external clock source (USCK/SCL). When software
strobe or timer/counter0 compare match clock option is selected, the output latch is transparent and therefore the output is
changed immediately. Clearing the USICS1..0 bits enables software strobe option. When using this option, writing a one to
the USICLK bit clocks both the shift register and the counter. For external clock source (USICS1 = 1), the USICLK bit is no
longer used as a strobe, but selects between external clocking and software clocking by the USITC strobe bit.
Table 23-1. Relations between USIWM1..0 and the USI Operation
USIWM1 USIWM0 Description
0 0 Outputs, clock hold, and start detector disabled. Port pins operates as normal.
0 1
Three-wire mode. Uses DO, DI, and USCK pins.
The data output (DO) pin overrides the corresponding bit in the PORT register in this mode.
However, the corresponding DDR bit still controls the data direction. When the port pin is set
as input the pins pull-up is controlled by the PORT bit.
The data input (DI) and serial clock (USCK) pins do not affect the normal port operation.
When operating as master, clock pulses are software generated by toggling the PORT
register, while the data direction is set to output. The USITC bit in the USICR register can be
used for this purpose.
1 0
Two-wire mode. Uses SDA (DI) and SCL (USCK) pins(1).
The serial data (SDA) and the serial clock (SCL) pins are bi-directional and uses open-
collector output drives. The output drivers are enabled by setting the corresponding bit for
SDA and SCL in the DDR register.
When the output driver is enabled for the SDA pin, the output driver will force the line SDA
low if the output of the shift register or the corresponding bit in the PORT register is zero.
Otherwise the SDA line will not be driven (i.e., it is released). When the SCL pin output driver
is enabled the SCL line will be forced low if the corresponding bit in the PORT register is
zero, or by the start detector. Otherwise the SCL line will not be driven.
The SCL line is held low when a start detector detects a start condition and the output is
enabled. Clearing the start condition flag (USISIF) releases the line. The SDA and SCL pin
inputs is not affected by enabling this mode. Pull-ups on the SDA and SCL port pin are
disabled in Two-wire mode.
1 1
Two-wire mode. Uses SDA and SCL pins.
Same operation as for the two-wire mode described above, except that the SCL line is also
held low when a counter overflow occurs, and is held low until the counter overflow flag
(USIOIF) is cleared.
Note: 1. The DI and USCK pins are renamed to serial data (SDA) and serial clock (SCL) respectively to avoid confu-
sion between the modes of operation.
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Table 23-2 shows the relationship between the USICS1..0 and USICLK setting and clock source used for the shift register
and the 4-bit counter.
• Bit 1 – USICLK: Clock Strobe
Writing a one to this bit location strobes the shift register to shift one step and the counter to increment by one, provided that
the USICS1..0 bits are set to zero and by doing so the software clock strobe option is selected. The output will change
immediately when the clock strobe is executed, i.e., in the same instruction cycle. The value shifted into the shift register is
sampled the previous instruction cycle. The bit will be read as zero.
When an external clock source is selected (USICS1 = 1), the USICLK function is changed from a clock strobe to a clock
select register. Setting the USICLK bit in this case will select the USITC strobe bit as clock source for the 4-bit counter (see
Table 23-2).
• Bit 0 – USITC: Toggle Clock Port Pin
Writing a one to this bit location toggles the USCK/SCL value either from 0 to 1, or from 1 to 0. The toggling is independent
of the setting in the data direction register, but if the PORT value is to be shown on the pin the DDRE4 must be set as output
(to one). This feature allows easy clock generation when implementing master devices. The bit will be read as zero.
When an external clock source is selected (USICS1 = 1) and the USICLK bit is set to one, writing to the USITC strobe bit will
directly clock the 4-bit counter. This allows an early detection of when the transfer is done when operating as a master
device.
Table 23-2. Relations between the USICS1..0 and USICLK Setting
USICS1 USICS0 USICLK Shift Register Clock Source 4-bit Counter Clock Source
0 0 0 No Clock No Clock
0 0 1 Software clock strobe (USICLK) Software clock strobe (USICLK)
0 1 X Timer/Counter0 Compare Match Timer/Counter0 Compare Match
1 0 0 External, positive edge External, both edges
1 1 0 External, negative edge External, both edges
1 0 1 External, positive edge Software clock strobe (USITC)
1 1 1 External, negative edge Software clock strobe (USITC)
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24. 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 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 24-1.
Figure 24-1. Analog Comparator Block Diagram(1)
Note: 1. See Table 24-1.
24.1 Analog Comparator Multiplexed Input
When the analog to digital converter (ADC) is configurated as single ended input channel, 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), MUX1..0 in ADMUX select the input pin to replace
the negative input to the analog comparator, as shown in Table 24-1. If ACME is cleared or ADEN is set, AIN1 is applied to
the negative input to the analog comparator.
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
Table 24-1. Analog Comparator Multiplexed Input
ACME ADEN MUX4..0 Analog Comparator Negative Input
0 x xx AIN1
1 1 xx AIN1
1 0 00000 ADC0
1 0 00001 ADC1
1 0 00010 ADC2
1 0 00011 ADC3
1 0 00100 ADC4
1 0 00101 ADC5
1 0 00110 ADC6
1 0 00111 ADC7
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24.2 Register Description
24.2.1 ADCSRB – ADC Control and Status Register B
• 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 24.1 “Analog Comparator Multiplexed Input” on page 133.
24.2.2 ACSR – Analog Comparator Control and Status Register
• 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.
• 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.
Bit 7 6543210
0x03 (0x23) BIN ACME –ADLAR –ADTS2 ADTS1 ADTS0 ADCSRB
Read/Write R/W R/W R R/w R R/W R/W R/W
Initial Value0 0000000
Bit 76543210
0x08 (0x28) ACD ACBG ACO ACI ACIE ACIC ACIS1 ACIS0 ACSR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 N/A 0 0 0 0 0
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• 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 24-2.
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.
24.2.3 DIDR0 – Digital Input Disable Register 0
• Bits 1, 0 – ADC0D,ADC1D: ADC 1/0 Digital input buffer 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 24-2. 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.
Bit 76543210
0x01 (0x21) ADC7D ADC6D ADC5D ADC4D ADC3D ADC2D ADC1D ADC0D DIDR0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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25. Analog to Digital Converter
25.1 Features
●10-bit resolution
●1.0 LSB integral non-linearity
●±2 LSB absolute accuracy
●65 - 260µs conversion time
●Up to 76kSPS at maximum resolution
●Eight multiplexed single ended input channels
●Twelve differential input channels with selectable gain (1x, 20x)
●Temperature sensor input channel
●Optional left adjustment for ADC result readout
●0 - VCC ADC input voltage range
●1.1V ADC reference voltage
●Free running or single conversion mode
●ADC start conversion by auto triggering on interrupt sources
●Interrupt on ADC conversion complete
●Sleep mode noise canceler
●Unipolar / bipolar input mode
●Input polarity reversal channels
25.2 Overview
The ATtiny24/44/84 features a 10-bit successive approximation ADC. The ADC is connected to 8-pin port A for external
sources. In addition to external sources internal temperature sensor can be measured by ADC. Analog multiplexer allows
eight single-ended channels or 12 differential channels from port A. The programmable gain stage provides amplification
steps 0 dB (1x) and 26 dB (20x) for 12 differential ADC channels.
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 25-1 on page 137.
Internal reference voltage of nominally 1.1V is provided On-chip. Alternatively, VCC can be used as reference voltage for
single ended channels. There is also an option to use an external voltage reference and turn-off the internal voltage
reference.
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Figure 25-1. Analog to Digital Converter Block Schematic
Prescaler START
BIN
Single Ended/ Differential Selection
IPR
ADC8
-
+
15 0
ADC Multiplexer
Select (ADMUX)
Trigger
Select
MUX Decoder
VCC
ADTS2 to ADTS0
8-bit Data Bus
Interrupt
Flags
AREF
10-bit DAC
Sample and Hold
Comparator
Gain
Amplifier
Internal
Reference
1.1V
Temperature
Sensor
Conversion Logic
ADC CTRL & Status B
Register (ADCSRB)
ADC Conversion
Complete IRQ
ADC CTRL and Status A
Register (ADCSRA)
ADC Data Register
(ADCH/ADCL)
+
-
ADIF
ADEN
Channel Selection
Gain Selection
ADSC
MUX4...MUX0
REFS1...REFS0
ADLAR
ADIF
ADPS2
ADPS1
ADPS0
ADATE
ADIE
ADC[9:0]
ADC
MULTIPLEXER
OUTPUT
A
DC7
A
DC6
A
DC5
A
DC4
A
DC3
A
DC2
A
DC1
A
DC0
AGND
POS.
Input
MUX
NEG.
Input
MUX
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25.3 ADC 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 reference voltage.The voltage reference for the ADC may be
selected by writing to the REFS1..0 bits in ADMUX. The VCC supply, the AREF pin or an internal 1.1V voltage reference
may be selected as the ADC voltage reference.
The analog input channel and differential gain are selected by writing to the MUX5..0 bits in ADMUX. Any of the eight ADC
input pins ADC7..0 can be selected as single ended inputs to the ADC. For differential measurements all analog inputs next
to each other can be selected as a input pair. Every input is also possible to measure with ADC3. These pairs of differential
inputs are measured by ADC trough the differential gain amplifier.
If differential channels are selected, the differential gain stage amplifies the voltage difference between the selected input
pair by the selected gain factor, 1x or 20x, according to the setting of the MUX0 bit in ADMUX. This amplified value then
becomes the analog input to the ADC. If single ended channels are used, the gain amplifier is bypassed altogether.
The offset of the differential channels can be measure by selecting the same input for both negative and positive input.
Offset calibration can be done for ADC0, ADC3 and ADC7. When ADC0 or ADC3 or ADC7 is selected as both the positive
and negative input to the differential gain amplifier, the remaining offset in the gain stage and conversion circuitry can be
measured directly as the result of the conversion. This figure can be subtracted from subsequent conversions with the same
gain setting to reduce offset error to below 1 LSB.
The on-chip temperature sensor is selected by writing the code “100010” to the MUX5..0 bits in ADMUX register.
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.
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 ADCSRB.
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.
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25.4 Starting a Conversion
A single conversion is started by 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 25-2. 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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25.5 Prescaling and Conversion Timing
Figure 25-3. 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 10 bits 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 14.5 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 25-1 on page 142.
7-bit ADC Prescaler
ADC Clock Source
ADEN
START
CK
ADPS0
ADPS1
ADPS2
Reset
CK/2
CK/4
CK/8
CK/16
CK/32
CK/64
CK/128
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Figure 25-4. ADC Timing Diagram, First Conversion (Single Conversion Mode)
Figure 25-5. 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 25-6. ADC Timing Diagram, Auto Triggered Conversion
Figure 25-7. ADC Timing Diagram, Free Running Conversion
Table 25-1. ADC Conversion Time
Condition
Sample and Hold (Cycles from Start of
Conversion) Conversion Time (Cycles)
First conversion 14.5 25
Normal conversions 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
1112131234
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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25.6 Changing Channel or Reference Selection
The MUX5:0 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.
25.6.1 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.
25.6.2 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 VCC, or internal 1.1V reference, or external AREF pin.
The first ADC conversion result after switching reference voltage source may be inaccurate, and the user is advised to
discard this result.
25.7 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.
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25.7.1 Analog Input Circuitry
The analog input circuitry for single ended channels is illustrated in Figure 25-8 on page 144. 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 10kΩ 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 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 25-8. Analog Input Circuitry
25.7.2 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. Use the ADC noise canceler function to reduce induced noise from the CPU.
c. If any port pins are used as digital outputs, it is essential that these do not switch while a conversion is in progress.
IIL
VCC/2
CS/H = 14pF
IIH
ADCn
1 to 100kΩ
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25.7.3 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 0.5 LSB). Ideal value:
0 LSB.
Figure 25-9. 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 1.5 LSB below maximum). Ideal value: 0 LSB
Figure 25-10.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: 0 LSB.
Figure 25-11.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 (1 LSB). Ideal value: 0 LSB.
Figure 25-12.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
(1 LSB wide) will code to the same value. Always ± 0.5 LSB.
●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: ± 0.5 LSB.
Output Code
Ideal ADC
INL
Actual ADC
V
REF
Input Voltage
Output Code
0x3FF
0x000
0
1 LSB
DNL
V
REF
Input Voltage
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25.8 ADC Conversion Result
After the conversion is complete (ADIF is high), the conversion result can be found in the ADC result registers (ADCL,
ADCH). The form of the conversion result depends on the type of the conversion as there are three types of conversions:
single ended conversion, unipolar differential conversion and bipolar differential conversion.
25.8.1 Single Ended Conversion
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 25-3 on page 149 and
Table 25-4 on page 150). 0x000 represents analog ground, and 0x3FF represents the selected reference voltage minus one
LSB. The result is presented in one-sided form, from 0x3FF to 0x000.
25.8.2 Unipolar Differential Conversion
If differential channels and an unipolar input mode are used, the result is
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin, and VREF the selected voltage
reference. The voltage of the positive pin must always be larger than the voltage of the negative pin or otherwise the voltage
difference is saturated to zero. The result is presented in one-sided form, from 0x000 (0d) through 0x3FF (+1023d). The
GAIN is either 1x or 20x.
ADC VIN 1024⋅
VREF
-------------------------
=
ADC VPOS VNEG
–()1024⋅
VREF
-------------------------------------------------------GAIN⋅=
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25.8.3 Bipolar Differential Conversion
If differential channels and a bipolar input mode are used, the result is
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin, and VREF the selected voltage
reference. The result is presented in two’s complement form, from 0x200 (–512d) through 0x1FF (+511d). The GAIN is
either 1x or 20x. Note that if the user wants to perform a quick polarity check of the result, it is sufficient to read the MSB of
the result (ADC9 in ADCH). If the bit is one, the result is negative, and if this bit is zero, the result is positive.
As default the ADC converter operates in the unipolar input mode, but the bipolar input mode can be selected by writing the
BIN bit in the ADCSRB to one. In the bipolar input mode two-sided voltage differences are allowed and thus the voltage on
the negative input pin can also be larger than the voltage on the positive input pin.
25.9 Temperature Measurement
The temperature measurement is based on an on-chip temperature sensor that is coupled to a single ended ADC8 channel.
Selecting the ADC8 channel by writing the MUX5:0 bits in ADMUX register to “100010” enables the temperature sensor. The
internal 1.1V reference must also be selected for the ADC reference source in the temperature sensor measurement. When
the temperature sensor is enabled, the ADC converter can be used in single conversion mode to measure the voltage over
the temperature sensor. The measured voltage has a linear relationship to the temperature as described in Table 25-2.
The voltage sensitivity is approximately 1mV/°C and the accuracy of the temperature measurement is ±10°C after offset
calibration. Bandgap is always calibrated and its accuracy is only guaranteed between 1.0V and 1.2V.
The values described in Table 25-2 are typical values. However, due to the process variation the temperature sensor output
voltage varies from one chip to another. To be capable of achieving more accurate results the temperature measurement
can be calibrated in the application software. The software calibration requires that a calibration value is measured and
stored in a register or EEPROM for each chip, as a part of the production test. The software calibration can be done utilizing
the formula:
T = {[(ADCH << 8) | ADCL] - TOS} / k
where ADCn are the ADC data registers, k is a fixed coefficient and TOS is the temperature sensor offset value determined
and stored into EEPROM as a part of the production test.To obtain best accuracy the coefficient k should be measured using
two temperature calibrations. Using offset calibration, set k = 1.0, where k = (1024 × 1.07mV/°C)/1.1V~1.0 [1/°C].
ADC VPOS VNEG
–()512⋅
VREF
----------------------------------------------------GAIN⋅=
Table 25-2. Temperature versus Sensor Output Voltage (Typical Case)
Temperature / °C –40°C +25°C +85°C +125°C
Voltage / mV 243mV 314mv 380mV 424mV
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25.10 Register Description
25.10.1 ADMUX – ADC Multiplexer Selection Register
• Bit 7:6 – REFS1:REFS0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in Table 25-3. If these bits are changed during a conversion,
the change will not go in effect until this conversion is complete (ADIF in ADCSR is set).
Special care should be taken when changing differential channels. Once a differential channel has been selected, the stage
may take as much as 25 ADC clock cycles to stabilize to the new value. Thus conversions should not be started within the
first 13 clock cycles after selecting a new differential channel. Alternatively, conversion results obtained within this period
should be discarded.
The same settling time should be observed for the first differential conversion after changing ADC reference (by changing
the REFS1:0 bits in ADMUX).
If channels where differential gain is used ie. the gainstage, using VCC or an optional external AREF higher than (VCC –1V) is
not recommended, as this will affect ADC accuracy. It is not allowed to connect internal voltage reference to AREF pin, if an
external voltage is being applied to it already. Internal voltage reference is connected AREF pin when REFS1:0 is set to
value ‘11’.
Bit 76543210
0x07 (0x27) REFS1 REFS0 MUX5 MUX4 MUX3 MUX2 MUX1 MUX0 ADMUX
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Table 25-3. Voltage Reference Selections for ADC
REFS1 REFS0 Voltage Reference Selection
0 0 VCC used as analog reference, disconnected from PA0 (AREF)
0 1 External voltage reference at PA0 (AREF) pin, internal voltage reference turned off
1 0 Internal 1.1V voltage reference
1 1 Reserved
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• Bits 5:0 – MUX5:0: Analog Channel and Gain Selection Bits
The value of these bits selects which combination of analog inputs are connected to the ADC. In case of differential input,
gain selection is also made with these bits. Selections on Table 25-4 show values for single ended channels and where the
differential channels as well as the offset calibration selections are located. Selecting the single-ended channel ADC8
enables the temperature measurement. See Table 25-4 for details. If these bits are changed during a conversion, the change
will not go into effect until this conversion is complete (ADIF in ADCSRA is set).
Table 25-4. Single Endid Input channel Selections.
Single Ended Input MUX5..0
ADC0 (PA0) 000000
ADC1 (PA1) 000001
ADC2 (PA2) 000010
ADC3 (PA3) 000011
ADC4 (PA4) 000100
ADC5 (PA5) 000101
ADC6 (PA6) 000110
ADC7 (PA7) 000111
Reserved for differential channels(1) 001000 - 011111
0V (AGND) 100000
1.1V (I Ref) 100001
ADC8(2) 100010
Reserved for offset calibration(3) 100011 - 100111
Reserved for reversal differential channels(1) 101000 - 111111
Notes: 1. See Table 25-5 on page 151 for details.
2. See Section 25.9 “Temperature Measurement” on page 148.
3. For offset calibration only. See Table 25-5 on page 151 and Section 25.3 “ADC Operation” on page 138.
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See Table 25-5 for details of selections of differential input channel selections as well as selections of offset calibration
channels. MUX0 bit works as a gain selection bit for differential channels shown in Table 25-5. When MUX0 bit is cleared
(‘0’) 1x gain is selected and when it is set (‘1’) 20x gain is selected. For normal differential channel pairs MUX5 bit work as a
polarity reversal bit. Togling of the MUX5 bit exhanges the positive and negative channel other way a round.
For offset calibration purpose the offset of the certain differential channels can be measure by selecting the same input for
both negative and positive input. This calibration can be done for ADC0, ADC3 and ADC7.
Section 25.3 “ADC Operation” on page 138 describes offset calibration in a more detailed level.
Table 25-5. Differential Input channel Selections.
Positive Differential Input Negative Differential Input
MUX5..0
Gain 1x Gain 20x
ADC0 (PA0)
ADC0 (PA0)(1) N/A 100011
ADC1 (PA1) 001000 001001
ADC3 (PA3) 001010 001011
ADC1 (PA1)
ADC0 (PA0) 101000 101001
ADC2 (PA2) 001100 001101
ADC3 (PA3) 001110 001111
ADC2 (PA2) ADC1 (PA1) 101100 101101
ADC3 (PA3) 010000 010001
ADC3 (PA3)
ADC0 (PA0) 101010 101011
ADC1 (PA1) 101110 101111
ADC2 (PA2) 110000 110001
ADC3 (PA3)(1) 100100 100101
ADC4 (PA4 010010 010011
ADC5 (PA5) 010100 010101
ADC6 (PA6) 010110 010111
ADC7 (PA7) 011000 011001
ADC4 (PA4 ADC3 (PA3) 110010 110011
ADC5 (PA5) 011010 011011
ADC5 (PA5)
ADC3 (PA3) 110100 110101
ADC4 (PA4) 111010 111011
ADC6 (PA6) 011100 011101
ADC6 (PA6)
ADC3 (PA3) 110110 110111
ADC5 (PA5) 111100 111101
ADC7 (PA7) 011110 011111
ADC7 (PA7)
ADC3 (PA3) 111000 111001
ADC6 (PA6) 111110 111111
ADC7 (PA7)(1) 100110 100111
Notes: 1. For offset calibration only. See Section 25.3 “ADC Operation” on page 138
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25.10.2 ADCSRA – ADC Control and Status Register A
• 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 instruction is used.
• 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.
Bit 76543210
0x06 (0x26) 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
Table 25-6. 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
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25.10.3 ADCL and ADCH – ADC Data Register
25.10.3.1 ADLAR = 0
25.10.3.2 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 ADCSRB, 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 25.8 “ADC Conversion Result” on page 147.
25.10.4 ADCSRB – ADC Control and Status Register B
• Bits 7 – BIN: Bipolar Input Mode
The gain stage is working in the unipolar mode as default, but the bipolar mode can be selected by writing the BIN bit in the
ADCSRB register. In the unipolar mode only one-sided conversions are supported and the voltage on the positive input must
always be larger than the voltage on the negative input. Otherwise the result is saturated to the voltage reference. In the
bipolar mode two-sided conversions are supported and the result is represented in the two’s complement form. In the
unipolar mode the resolution is 10 bits and the bipolar mode the resolution is 9 bits + 1 sign bit.
• Bit 6 – ACME: Analog Comparator Multiplexer Enable
See Section 24.2.1 “ADCSRB – ADC Control and Status Register B” on page 134.
• Bit 5 – Res: Reserved Bit
This bit is reserved bit in the Atmel® ATtiny24/44/84 and will always read as what was wrote there.
Bit 151413121110 9 8
0x05 (0x25) – – – – – – ADC9 ADC8 ADCH
0x04 (0x24) ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADC1 ADC0 ADCL
76543210
Read/WriteRRRRRRRR
RRRRRRRR
Initial Value00000000
00000000
Bit 151413121110 9 8
0x05 (0x25) ADC9 ADC8 ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADCH
0x04 (0x24) ADC1 ADC0 – – – – – – ADCL
76543210
Read/WriteRRRRRRRR
RRRRRRRR
Initial Value00000000
00000000
Bit 76543210
0x03 (0x23) BIN ACME – ADLAR – ADTS2 ADTS1 ADTS0 ADCSRB
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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• Bit 4 – 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 25.10.3 “ADCL and ADCH – ADC Data Register” on page 153.
• Bit 3 – Res: Reserved Bit
This bit is reserved bit in the Atmel ATtiny24/44/84 and will always read as what was wrote there.
• Bits 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.
25.10.5 DIDR0 – Digital Input Disable Register 0
• Bits 7..0 – ADC7D..ADC0D: ADC7..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 ADC7..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 25-7. 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
0x01 (0x21) ADC7D ADC6D ADC5D ADC4D ADC3D ADC2D ADC1D ADC0D DIDR0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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26. debugWIRE On-chip Debug System
26.1 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
26.2 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.
26.3 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 26-1. The debugWIRE Setup
Figure 26-1 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 resistor on the dW/(RESET) line must be in the range of 10k to 20kΩ. However, the pull-up resistor is optional.
●Connecting the RESET pin directly to VCC will not work.
●Capacitors inserted on the RESET pin must be disconnected when using debugWire.
●All external reset sources must be disconnected.
GND
dw (RESET)
VCC
dw
1.8 to 5.5V
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26.4 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.
26.5 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). See the debugWIRE documentation for detailed description of the limitations.
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.
26.6 Register Description
The following section describes the registers used with the debugWire.
26.6.1 DWDR – debugWire Data Register
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.
Bit 76543210
0x27 (0x47) DWDR[7:0] DWDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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27. Self-Programming the Flash
The device provides a self-programming mechanism for downloading and uploading program code by the MCU itself. The
self-programming can use any available data interface and associated protocol to read code and write (program) that code
into the program memory.
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 re-written. 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.
27.0.1 Performing Page Erase by SPM
To execute page erase, set up the address in the Z-pointer, write “00000011” 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.
●The CPU is halted during the page erase operation.
27.0.2 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 CTPB 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.
27.0.3 Performing a Page Write
To execute page write, set up the address in the Z-pointer, write “00000101” 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.
●The CPU is halted during the page write operation.
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27.1 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 28-7 on page 164), 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 is shown in Figure 28-1 on page 164. Note that the page erase and page write
operations are addressed independently. Therefore it is of major importance that the software addresses the same page in
both the page erase and page write operation.
The LPM instruction uses 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.
Figure 27-1. Addressing the Flash During SPM(1)
Notes: 1. The different variables used in Figure 27-1 are listed in Table 28-7 on page 164.
27.1.1 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.
27.1.2 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 RFLB and SPMEN bits in SPMCSR. When an LPM instruction is executed within three CPU cycles after the RFLB and
SPMEN bits are set in SPMCSR, the value of the lock bits will be loaded in the destination register. The RFLB and SPMEN
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 RFLB and SPMEN are cleared, LPM will work as described in the
instruction set manual.
Bit 151413121110 9 8
ZH (R31) Z15 Z14 Z13 Z12 Z11 Z10 Z9 Z8
ZL (R30)Z7Z6Z5Z4Z3Z2Z1Z0
76543210
Bit
PAGEMSBPCMSB
ZPAGEMSBZPCMSB 0115
Z-register
Program
Counter
Page Address
within the Flash
Word Address
within a Page
0
PCWORDPCPAGE
02
01
00
PAGEEND
PCWORD[PAGEMSB:0]
Page
Program Memory
Instruction Word
Page
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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 RFLB and SPMEN bits in SPMCSR. When an LPM instruction is
executed within three cycles after the RFLB and SPMEN bits are set in the SPMCSR, the value of the fuse low byte (FLB)
will be loaded in the destination register as shown below. See Table 28-5 on page 163 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 RFLB and SPMEN bits are set in the SPMCSR, the value of the fuse high byte (FHB) will be loaded in the
destination register as shown below. See Table 28-4 on page 162 for detailed description and mapping of the fuse high 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.
27.1.3 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. 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.
2. 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.
27.1.4 Programming Time for Flash when Using SPM
The calibrated RC oscillator is used to time flash accesses. Table 27-1 shows the typical programming time for flash
accesses from the CPU.
Bit 76543210
Rd ––––––LB2LB1
Bit 76543210
Rd FLB7 FLB6 FLB5 FLB4 FLB3 FLB2 FLB1 FLB0
Bit 76543210
Rd FHB7 FHB6 FHB5 FHB4 FHB3 FHB2 FHB1 FHB0
Table 27-1. SPM Programming Time(1)
Symbol Min Programming Time Max Programming Time
Flash write (page erase, page write, and write lock
bits by SPM) 3.7ms 4.5ms
Note: 1. The min and max programming times is per individual operation.
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27.2 Register Description
27.2.1 SPMCSR – Store Program Memory Control and Status Register
The Store program memory control and status register contains the control bits needed to control the program memory
operations.
• Bits 7..5 – Res: Reserved Bits
These bits are reserved bits in the Atmel® ATtiny24/44/84 and always read as zero.
• Bit 4 – CTPB: Clear Temporary Page Buffer
If the CTPB bit is written while filling the temporary page buffer, the temporary page buffer will be cleared and the data will be
lost.
• Bit 3 – RFLB: Read Fuse and Lock Bits
An LPM instruction within three cycles after RFLB and SPMEN 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 27.1.1 “EEPROM Write Prevents Writing to SPMCSR” on page 158 for details.
• Bit 2 – PGWRT: Page Write
If this bit is written to one at the same time as SPMEN, 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.
• Bit 1 – PGERS: Page Erase
If this bit is written to one at the same time as SPMEN, 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.
• Bit 0 – SPMEN: Store Program Memory Enable
This bit enables the SPM instruction for the next four clock cycles. If written to one together with either CTPB, RFLB,
PGWRT, or PGERS, the following SPM instruction will have a special meaning, see description above. If only SPMEN 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 SPMEN 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 SPMEN 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.
Bit 7 65 4 3210
0x37 (0x57) – – – CTPB RFLB PGWRT PGERS SPMEN SPMCSR
Read/Write R 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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28. Memory Programming
This section describes the different methods for programming the Atmel® ATtiny24/44/84 memories.
28.1 Program And Data Memory Lock Bits
The Atmel ATtiny24/44/84 provides two lock bits which can be left unprogrammed (“1”) or can be programmed (“0”) to obtain
the additional security listed in Table 28-2 on page 161. The lock bits can only be erased to “1” with the chip erase command.
Program memory can be read out via the debugWIRE interface when the DWEN fuse is programmed, even if the lock bits
are set. Thus, when lock bit security is required, should always debugWIRE be disabled by clearing the DWEN fuse.
Table 28-1. Lock Bit Byte(1)
Lock Bit Byte Bit No Description Default Value
7 – 1 (unprogrammed)
6 – 1 (unprogrammed)
5 – 1 (unprogrammed)
4 – 1 (unprogrammed)
3 – 1 (unprogrammed)
2 – 1 (unprogrammed)
LB2 1Lock bit 1 (unprogrammed)
LB1 0Lock bit 1 (unprogrammed)
Notes: 1. “1” means unprogrammed, “0” means programmed.
Table 28-2. 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 high-voltage
and serial programming mode. The fuse bits are locked in both serial and
high-voltage programming mode(1). debugWire is disabled.
3 0 0
Further programming and verification of the flash and EEPROM is disabled in
high-voltage and serial programming mode. The fuse bits are locked in both
serial and high-voltage programming mode(1). debugWire is disabled.
Notes: 1. Program the Fuse bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
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28.2 Fuse Bytes
The Atmel® ATtiny24/44/84 has three fuse bytes. Table 28-4 to Table 28-5 on page 163 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 28-3. Fuse Extended Byte
Fuse High Byte Bit No Description Default Value
7 - 1 (unprogrammed)
6 - 1 (unprogrammed)
5 - 1 (unprogrammed)
4 - 1 (unprogrammed)
3 - 1 (unprogrammed)
2 - 1 (unprogrammed)
1 - 1 (unprogrammed)
SELFPRGEN 0Self-programming enable 1 (unprogrammed)
Table 28-4. Fuse High Byte
Fuse High Byte Bit No Description Default Value
RSTDISBL(1) 7External reset disable 1 (unprogrammed)
DWEN(2) 6DebugWIRE enable 1 (unprogrammed)
SPIEN(3) 6Enable serial program and data downloading 0 (programmed, SPI prog.
enabled)
WDTON(4) 4Watchdog timer always on 1 (unprogrammed)
EESAVE 3EEPROM memory is preserved through the chip
erase
1 (unprogrammed, EEPROM
not preserved)
BODLEVEL2(5) 2Brown-out detector trigger level 1 (unprogrammed)
BODLEVEL1(5) 1Brown-out detector trigger level 1 (unprogrammed)
BODLEVEL0(5) 0Brown-out detector trigger level 1 (unprogrammed)
Notes: 1. See Section 19.3.2 “Alternate Functions of Port B” on page 74 for description of RSTDISBL and DWEN
Fuses. When programming the RSTDISBL fuse, high-voltage serial programming has to be used to change
fuses to perform further programming.
2. DWEN must be unprogrammed when lock bit security is required.
See Section 28.1 “Program And Data Memory Lock Bits” on page 161.
3. The SPIEN fuse is not accessible in SPI programming mode.
4. See Section 16-2 “WDT Configuration as a Function of the Fuse Settings of WDTON” on page 54 for details.
5. See Table 29-4 on page 178 for BODLEVEL fuse decoding.
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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.
28.2.1 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.
28.3 Signature Bytes
All Atmel® microcontrollers have a three-byte signature code which identifies the device. This code can be read in both serial
and high-voltage programming mode, also when the device is locked. The three bytes reside in a separate address space.
For the Atmel ATtiny24/44/84 the signature bytes are given in Table 28-6.
Table 28-5. Fuse Low Byte
Fuse Low Byte Bit No Description Default Value
CKDIV8(1) 7Divide clock by 8 0 (programmed)
CKOUT 6Clock output enable 1 (unprogrammed)
SUT1 5Select start-up time 1 (unprogrammed)(2)
SUT0 4Select start-up time 0 (programmed)(2)
CKSEL3 3Select clock source 0 (programmed)(3)
CKSEL2 2Select clock source 0 (programmed)(3)
CKSEL1 1Select clock source 1 (unprogrammed)(3)
CKSEL0 0Select clock source 0 (programmed)(3)
Notes: 1. See Section 14.9 “System Clock Prescaler” on page 43 for details.
2. The default value of SUT1..0 results in maximum start-up time for the default clock source.
See Table 14-7 on page 41 for details.
3. The default setting of CKSEL3..0 results in internal RC oscillator at 8.0MHz. See Table 14-6 on page 41 for
details.
Table 28-6. Device ID
Parts
Signature Bytes Address
0x000 0x001 0x002
ATtiny24 0x1E 0x91 0x0B
ATtiny44 0x1E 0x92 0x07
ATtiny84 0x1E 0x93 0x0C
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28.4 Calibration Byte
Signature area of the Atmel ATtiny24/44/84 has one byte of calibration data for the internal RC oscillator. This byte resides in
the high byte of address 0x000. During reset, this byte is automatically written into the OSCCAL register to ensure correct
frequency of the calibrated RC oscillator.
28.5 Page Size
28.6 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 28-9 on page 164,
the pin mapping for SPI programming is listed. Not all parts use the SPI pins dedicated for the internal SPI interface.
Figure 28-1. 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 CLKI pin
Table 28-7. No. of Words in a Page and No. of Pages in the Flash
Device Flash Size Page Size PCWORD No. of Pages PCPAGE PCMSB
ATtiny24 1Kwords (2Kbytes) 16 words PC[3:0] 64 PC[9:4] 9
ATtiny44 2Kwords (4Kbytes) 32 words PC[4:0] 64 PC[10:5] 10
ATtiny84 4Kwords (8Kbytes) 32 words PC[4:0] 128 PC[11:5] 11
Table 28-8. No. of Words in a Page and No. of Pages in the EEPROM
Device EEPROM Size Page Size PCWORD No. of Pages PCPAGE EEAMSB
ATtiny24 128 bytes 4 bytes EEA[1:0] 32 EEA[6:2] 6
ATtiny44 256 bytes 4 bytes EEA[1:0] 64 EEA[7:2] 7
ATtiny84 512 bytes 4 bytes EEA[1:0] 128 EEA[8:2] 8
Table 28-9. Pin Mapping Serial Programming
Symbol Pins I/O Description
MOSI PA6 ISerial data in
MISO PA5 OSerial data out
SCK PA4 ISerial clock
GND
RESET
VCC
+1.8V to 5.5V
MOSI
MISO
SCK
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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: > 2CPU clock cycles for fck < 12MHz, 3CPU clock cycles for fck ≥ 12MHz
High: > 2CPU clock cycles for fck < 12MHz, 3CPU clock cycles for fck ≥ 12MHz
28.6.1 Serial Programming Algorithm
When writing serial data to the Atmel® ATtiny24/44/84, data is clocked on the rising edge of SCK.
When reading data from the Atmel ATtiny24/44/84, data is clocked on the falling edge of SCK. See Figure 29-3 on page 181
and Figure 29-4 on page 181 for timing details.
To program and verify the Atmel ATtiny24/44/84 in the serial programming mode, the following sequence is recommended
(see four byte instruction formats in Table 28-11 on page 166):
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 20 ms and enable serial programming by sending the programming enable serial instruction to pin
MOSI.
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 5
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 3MSB of the address. If
polling (RDY/BSY) is not used, the user must wait at least tWD_FLASH before issuing the next page.
(See Table 28-10 on page 166.) Accessing the serial programming interface before the flash write operation com-
pletes can result in incorrect programming.
5. A: 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 (RDY/BSY) is not used, the user must wait at least tWD_EEPROM before issuing the next byte.
(See Table 28-10 on page 166.) In a chip erased device, no 0xFFs in the data file(s) need to be programmed.
B: The EEPROM array is programmed one page at a time. The memory page is loaded one byte at a time by sup-
plying the 2LSB of the address and data together with the load EEPROM memory page instruction. The EEPROM
memory page is stored by loading the write EEPROM memory page instruction with the 4MSB of the address.
When using EEPROM page access only byte locations loaded with the load EEPROM memory page instruction is
altered. The remaining locations remain unchanged. If polling (RDY/BSY) is not used, the used must wait at least
tWD_EEPROM before issuing the next page (See Table 28-10 on page 166). In a chip erased device, no 0xFF 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.
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28.6.2 Serial Programming Instruction set
Table 28-11 on page 166 and Figure 28-2 on page 167 describes the Instruction set
.
Table 28-10. Minimum Wait Delay Before Writing the Next Flash or EEPROM Location
Symbol Minimum Wait Delay
tWD_FLASH 4.5ms
tWD_EEPROM 4.0ms
tWD_ERASE 4.0ms
tWD_FUSE 4.5ms
Table 28-11. Serial Programming Instruction Set
Instruction/Operation(1)
Instruction Format
Byte 1 Byte 2 Byte 3 Byte4
Programming enable $AC $53 $00 $00
Chip erase (program memory/EEPROM) $AC $80 $00 $00
Poll RDY/BSY $F0 $00 $00 data byte out
Load instructions
Load extended address byte $4D $00 Extended adr $00
Load program memory page, high byte $48 adr MSB adr LSB high data byte in
Load program memory page, low byte $40 adr MSB adr LSB low data byte in
Load EEPROM memory page (Page
access) $C1 $00 adr LSB data byte in
Read instructions
Read program memory, high byte $28 adr MSB adr LSB high data byte out
Read program memory, low byte $20 adr MSB adr LSB low data byte out
Read EEPROM memory $A0 $00 adr LSB data byte out
Read lock bits $58 $00 $00 data byte out
Read signature byte $30 $00 adr LSB data byte out
Read fuse bits $50 $00 $00 data byte out
Read fuse high bits $58 $08 $00 data byte out
Read extended fuse bits $50 $08 $00 data byte out
Read calibration byte $38 $00 $00 data byte out
Write instructions(6)
Write program memory page $4C adr MSB adr LSB $00
Write EEPROM memory $C0 $00 adr LSB data byte in
Write EEPROM memory Page (page
access) $C2 $00 adr LSB $00
Notes: 1. Not all instructions are applicable for all parts.
2. a = address
3. Bits are programmed ‘0’, unprogrammed ‘1’.
4. To ensure future compatibility, unused fuses and lock bits should be unprogrammed (‘1’).
5. Refer to the corresponding section for fuse and lock bits, calibration and signature bytes and page size.
6. Instructions accessing program memory use a word address. This address may be random within the page
range.
7. See http://www.atmel.com/avr for application notes regarding programming and programmers.
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If the LSB in RDY/BSY data byte out is ‘1’, a programming operation is still pending. Wait until this bit returns ‘0’ before the
next instruction is carried out.
Within the same page, the low data byte must be loaded prior to the high data byte.
After data is loaded to the page buffer, program the EEPROM page, see Figure 28-2.
Figure 28-2. Serial Programming Instruction example
Write lock bits $AC $E0 $00 data byte in
Write fuse bits $AC $A0 $00 data byte in
Write fuse high bits $AC $A8 $00 data byte in
Write extended fuse bits $AC $A4 $00 data byte in
Table 28-11. Serial Programming Instruction Set (Continued)
Instruction/Operation(1)
Instruction Format
Byte 1 Byte 2 Byte 3 Byte4
Notes: 1. Not all instructions are applicable for all parts.
2. a = address
3. Bits are programmed ‘0’, unprogrammed ‘1’.
4. To ensure future compatibility, unused fuses and lock bits should be unprogrammed (‘1’).
5. Refer to the corresponding section for fuse and lock bits, calibration and signature bytes and page size.
6. Instructions accessing program memory use a word address. This address may be random within the page
range.
7. See http://www.atmel.com/avr for application notes regarding programming and programmers.
Byte 1 Byte 2 Byte 3 Byte 4
Page 0
Page 1
Page 2
Adr LBSAdr MBS
Bit 15 B 0 Bit 15 B 0
Byte 1 Byte 2 Byte 3 Byte 4
Adr LBSAdr MBS
Page N-1
Program Memory/
EEPROM Memory
Serial Programming Instruction
Page Buffer
Page Number
Page Offset
Load Program Memory Page (High/Low Byte)/
Load EEPROM Memory Page (page access)
Write Program Memory Page/
Write EEPROM Memory Page
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28.7 High-voltage Serial Programming
This section describes how to program and verify flash program memory, EEPROM data memory, lock bits and fuse bits in
the Atmel® ATtiny24/44/84.
Figure 28-3. High-voltage Serial Programming
The minimum period for the serial clock input (SCI) during high-voltage serial programming is 220ns.
Table 28-12. Pin Name Mapping
Signal Name in High-voltage Serial
Programming Mode Pin Name I/O Function
SDI PA6 ISerial data input
SII PA5 ISerial instruction input
SDO PA4 OSerial data output
SCI PB0 ISerial clock input (min. 220ns period)
Table 28-13. Pin Values Used to Enter Programming Mode
Pin Symbol Value
PA0 Prog_enable[0] 0
PA1 Prog_enable[1] 0
PA2 Prog_enable[2] 0
GND
PB0
PB3 (RESET) VCC
SCI SDO
SII
SDI
+ 1.8 to 5.5V
+ 11.5 to 12.5V
PA4
PA5
PA6
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28.8 High-voltage Serial Programming Algorithm
To program and verify the Atmel® ATtiny24/44/84 in the high-voltage serial programming mode, the following sequence is
recommended (See instruction formats in Table 28-15 on page 172):
28.8.1 Enter High-voltage Serial Programming Mode
The following algorithm puts the device in high-voltage serial programming mode:
1. Apply 4.5 - 5.5V between VCC and GND.
2. Set RESET pin to “0” and toggle SCI at least six times.
3. Set the prog_enable pins listed in Table 28-13 on page 168 to “000” and wait at least 100ns.
4. Apply VHVRST - 5.5V to RESET. Keep the prog_enable pins unchanged for at least tHVRST after the high-voltage has
been applied to ensure the prog_enable signature has been latched.
5. Shortly after latching the prog_enable signature, the device will actively output data on the prog_enable[2]/SDO
pin, and the resulting drive contention may increase the power consumption. To minimize this drive contention,
release the prog_enable[2] pin after tHVRST has elapsed.
6. Wait at least 50µs before giving any serial instructions on SDI/SII.
28.8.2 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.
28.8.3 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 re-programmed.
Notes: 1. The EEPROM memory is preserved during chip erase if the EESAVE fuse is programmed.
1. Load command “chip erase” (see Table 28-15 on page 172).
2. Wait after Instr. 3 until SDO goes high for the “chip erase” cycle to finish.
3. Load command “no operation”.
Table 28-14. High-voltage Reset Characteristics
Supply Voltage RESET Pin High-voltage Threshold
Minimum High-voltage Period for Latching
Prog_enable
VCC VHVRST tHVRST
4.5V 11.5V 100ns
5.5V 11.5V 100ns
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28.8.4 Programming the Flash
The flash is organized in pages, see Section 28.5 “Page Size” on page 164. 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:
1. Load command “write flash” (see Table 28-15 on page 172).
2. Load flash page buffer.
3. Load flash high address and program page. Wait after Instr. 3 until SDO goes high for the “page programming”
cycle to finish.
4. Repeat 2 through 3 until the entire flash is programmed or until all data has been programmed.
5. End page programming by loading command “no operation”.
When writing or reading serial data to the Atmel® ATtiny24/44/84, data is clocked on the rising edge of the serial clock, see
Figure 29-5 on page 182, Figure 28-3 on page 168 and Table 29-8 on page 182 for details.
Figure 28-4. Addressing the Flash which is Organized in Pages
Figure 28-5. High-voltage Serial Programming Waveforms
PAGEMSBPCMSB
Program
Counter
Word Address
within a Page
Page Address
within the Flash
PCWORDPCPAGE
02
01
00
PAGEEND
PCWORD[PAGEMSB:0]
Page
Program Memory
Instruction Word
Page
0123
MSB LSB
MSB LSB
MSB LSB
45678910
SDI
SII
SDO
SCI
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28.8.5 Programming the EEPROM
The EEPROM is organized in pages, see Table 29-7 on page 181. When programming the EEPROM, the 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 Table 28-15 on page 172):
1. Load Command “Write EEPROM”.
2. Load EEPROM page buffer.
3. Program EEPROM page. wait after Instr. 2 until SDO goes high for the “page programming” cycle to finish.
4. Repeat 2 through 3 until the entire EEPROM is programmed or until all data has been programmed.
5. End page programming by loading command “no operation”.
28.8.6 Reading the Flash
The algorithm for reading the flash memory is as follows (refer to Table 28-15 on page 172):
1. Load Command “read flash”.
2. Read flash low and high bytes. The contents at the selected address are available at serial output SDO.
28.8.7 Reading the EEPROM
The algorithm for reading the EEPROM memory is as follows (refer to Table 28-15 on page 172):
1. Load command “read EEPROM”.
2. Read EEPROM byte. The contents at the selected address are available at serial output SDO.
28.8.8 Programming and Reading the Fuse and Lock Bits
The algorithms for programming and reading the fuse low/high bits and lock bits are shown in Table 28-15 on page 172.
28.8.9 Reading the Signature Bytes and Calibration Byte
The algorithms for reading the signature bytes and calibration byte are shown in Table 28-15 on page 172.
28.8.10 Power-off sequence
Set SCI to “0”. Set RESET to “1”. Turn VCC power off.
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Table 28-15. High-voltage Serial Programming Instruction Set for ATtiny24/44/84
Instruction
Instruction Format
Operation RemarksInstr.1/5 Instr.2/6 Instr.3/7 Instr.4
Chip Erase
SDI
SII
SDO
0_1000_0000_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_0100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
x_xxxx_xxxx_xx
Wait after Instr.3 until SDO
goes high for the Chip Erase
cycle to finish.
Load “Write
Flash”
Command
SDI
SII
SDO
0_0001_0000_00
0_0100_1100_00
x_xxxx_xxxx_xx
Enter Flash Programming
code.
Load Flash
Page Buffer
SDI
SII
SDO
0_ bbbb_bbbb _00
0_0000_1100_00
x_xxxx_xxxx_xx
0_eeee_eeee_00
0_0010_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1101_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
x_xxxx_xxxx_xx
Repeat after Instr. 1 - 7until the
entire page buffer is filled or
until all data within the page is
filled. See Note 1.
SDI
SII
SDO
0_dddd_dddd_00
0_0011_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1101_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1100_00
x_xxxx_xxxx_xx
Instr 5-7.
Load Flash
High Address
and Program
Page
SDI
SII
SDO
0_0000_000a_00
0_0001_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_0100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
x_xxxx_xxxx_xx
Wait after Instr 3 until SDO
goes high. Repeat Instr. 2 - 3
for each loaded Flash Page
until the entire Flash or all data
is programmed. Repeat Instr. 1
for a new 256 byte page. See
Note 1.
Load “Read
Flash”
Command
SDI
SII
SDO
0_0000_0010_00
0_0100_1100_00
x_xxxx_xxxx_xx
Enter Flash Read mode.
Read Flash
Low and High
Bytes
SDI
SII
SDO
0_bbbb_bbbb_00
0_0000_1100_00
x_xxxx_xxxx_xx
0_0000_000a_00
0_0001_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1000_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
q_qqqq_qqqx_xx
Repeat Instr. 1, 3 - 6 for each
new address. Repeat Instr. 2
for a new 256 byte page.
SDI
SII
SDO
0_0000_0000_00
0_0111_1000_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1100_00
p_pppp_pppx_xx
Instr 5 - 6.
Load “Write
EEPROM”
Command
SDI
SII
SDO
0_0001_0001_00
0_0100_1100_00
x_xxxx_xxxx_xx
Enter EEPROM Programming
mode.
Load
EEPROM
Page Buffer
SDI
SII
SDO
0_bbbb_bbbb_00
0_0000_1100_00
x_xxxx_xxxx_xx
0_aaaa_aaaa_00
0_0001_1100_00
x_xxxx_xxxx_xx
0_eeee_eeee_00
0_0010_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1101_00
x_xxxx_xxxx_xx
Repeat Instr. 1 - 5 until the
entire page buffer is filled or
until all data within the page is
filled. See Note 2.
SDI
SII
SDO
0_0000_0000_00
0_0110_1100_00
x_xxxx_xxxx_xx
a = address high bits, b = address low bits, d = data in high bits, e = data in low bits, p = data out high bits,
q = data out low bits, x = don’t care, 1 = Lock Bit1, 2 = Lock Bit2, 3 = CKSEL0 Fuse, 4 = CKSEL1 Fuse,
5 = CKSEL2 Fuse, 6 = CKSEL3 Fuse, 7 = SUT0 Fuse, 8 = SUT1 Fuse, 9 = CKDIV8 Fuse, A = CKOUT Fuse,
B = BODLEVEL0 Fuse, C = BODLEVEL1 Fuse, D= BODLEVEL2 Fuse, E = EESAVE Fuse, F = WDTON Fuse,
G = SPIEN Fuse, H = DWEN Fuse, I = RSTDISBL Fuse
Notes: 1. For page sizes less than 256 words, parts of the address (bbbb_bbbb) will be parts of the page address.
2. For page sizes less than 256 bytes, parts of the address (bbbb_bbbb) will be parts of the page address.
3. The EEPROM is written page-wise. But only the bytes that are loaded into the page are actually written to the
EEPROM. Page-wise EEPROM access is more efficient when multiple bytes are to be written to the same
page. Note that auto-erase of EEPROM is not available in High-voltage Serial Programming, only in SPI
Programming.
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Program
EEPROM
Page
SDI
SII
SDO
0_0000_0000_00
0_0110_0100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
x_xxxx_xxxx_xx
Wait after Instr. 2 until SDO
goes high. Repeat Instr. 1 - 2
for each loaded EEPROM
page until the entire EEPROM
or all data is programmed.
Write
EEPROM Byte
SDI
SII
SDO
0_bbbb_bbbb_00
0_0000_1100_00
x_xxxx_xxxx_xx
0_aaaa_aaaa_00
0_0001_1100_00
x_xxxx_xxxx_xx
0_eeee_eeee_00
0_0010_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1101_00
x_xxxx_xxxx_xx
Repeat Instr. 1 - 6 for each
new address. Wait after Instr. 6
until SDO goes high. See Note
3.
SDI
SII
SDO
0_0000_0000_00
0_0110_0100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
x_xxxx_xxxx_xx
Instr. 5-6
Load “Read
EEPROM”
Command
SDI
SII
SDO
0_0000_0011_00
0_0100_1100_00
x_xxxx_xxxx_xx
Enter EEPROM Read mode.
Read
EEPROM Byte
SDI
SII
SDO
0_bbbb_bbbb_00
0_0000_1100_00
x_xxxx_xxxx_xx
0_aaaa_aaaa_00
0_0001_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1000_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
q_qqqq_qqq0_00
Repeat Instr. 1, 3 - 4 for each
new address. Repeat Instr. 2
for a new 256 byte page.
Write Fuse
Low Bits
SDI
SII
SDO
0_0100_0000_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_A987_6543_00
0_0010_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_0100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
x_xxxx_xxxx_xx
Wait after Instr. 4 until SDO
goes high. Write A - 3 = “0” to
program the Fuse bit.
Write Fuse
High Bits
SDI
SII
SDO
0_0100_0000_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_IHGF_EDCB_00
0_0010_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_0100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1100_00
x_xxxx_xxxx_xx
Wait after Instr. 4 until SDO
goes high. Write F - B = “0” to
program the Fuse bit.
Write Fuse
Extended Bits
SDI
SII
SDO
0_0100_0000_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_000J_00
0_0010_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_0110_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1110_00
x_xxxx_xxxx_xx
Wait after Instr. 4 until SDO
goes high. Write J = “0” to
program the Fuse bit.
Write Lock Bits
SDI
SII
SDO
0_0010_0000_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_0021_00
0_0010_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_0100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
x_xxxx_xxxx_xx
Wait after Instr. 4 until SDO
goes high. Write 2 - 1 = “0” to
program the Lock Bit.
Read Fuse
Low Bits
SDI
SII
SDO
0_0000_0100_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1000_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
A_9876_543x_xx
Reading A - 3 = “0” means the
Fuse bit is programmed.
Read Fuse
High Bits
SDI
SII
SDO
0_0000_0100_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1010_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1100_00
I_HGFE_DCBx_xx
Reading F - B = “0” means the
Fuse bit is programmed.
Table 28-15. High-voltage Serial Programming Instruction Set for ATtiny24/44/84 (Continued)
Instruction
Instruction Format
Operation RemarksInstr.1/5 Instr.2/6 Instr.3/7 Instr.4
a = address high bits, b = address low bits, d = data in high bits, e = data in low bits, p = data out high bits,
q = data out low bits, x = don’t care, 1 = Lock Bit1, 2 = Lock Bit2, 3 = CKSEL0 Fuse, 4 = CKSEL1 Fuse,
5 = CKSEL2 Fuse, 6 = CKSEL3 Fuse, 7 = SUT0 Fuse, 8 = SUT1 Fuse, 9 = CKDIV8 Fuse, A = CKOUT Fuse,
B = BODLEVEL0 Fuse, C = BODLEVEL1 Fuse, D= BODLEVEL2 Fuse, E = EESAVE Fuse, F = WDTON Fuse,
G = SPIEN Fuse, H = DWEN Fuse, I = RSTDISBL Fuse
Notes: 1. For page sizes less than 256 words, parts of the address (bbbb_bbbb) will be parts of the page address.
2. For page sizes less than 256 bytes, parts of the address (bbbb_bbbb) will be parts of the page address.
3. The EEPROM is written page-wise. But only the bytes that are loaded into the page are actually written to the
EEPROM. Page-wise EEPROM access is more efficient when multiple bytes are to be written to the same
page. Note that auto-erase of EEPROM is not available in High-voltage Serial Programming, only in SPI
Programming.
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Read Fuse
Extended Bits
SDI
SII
SDO
0_0000_0100_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1010_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1110_00
x_xxxx_xxJx_xx
Reading J = “0” means the
Fuse bit is programmed.
Read Lock Bits
SDI
SII
SDO
0_0000_0100_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1000_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
x_xxxx_x21x_xx
Reading 2, 1 = “0” means the
Lock bit is programmed.
Read
Signature
Bytes
SDI
SII
SDO
0_0000_1000_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_00bb_00
0_0000_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1000_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0110_1100_00
q_qqqq_qqqx_xx
Repeats Instr 2 4 for each
signature byte address.
Read
Calibration
Byte
SDI
SII
SDO
0_0000_1000_00
0_0100_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0000_1100_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1000_00
x_xxxx_xxxx_xx
0_0000_0000_00
0_0111_1100_00
p_pppp_pppx_xx
Load “No
Operation”
Command
SDI
SII
SDO
0_0000_0000_00
0_0100_1100_00
x_xxxx_xxxx_xx
Table 28-15. High-voltage Serial Programming Instruction Set for ATtiny24/44/84 (Continued)
Instruction
Instruction Format
Operation RemarksInstr.1/5 Instr.2/6 Instr.3/7 Instr.4
a = address high bits, b = address low bits, d = data in high bits, e = data in low bits, p = data out high bits,
q = data out low bits, x = don’t care, 1 = Lock Bit1, 2 = Lock Bit2, 3 = CKSEL0 Fuse, 4 = CKSEL1 Fuse,
5 = CKSEL2 Fuse, 6 = CKSEL3 Fuse, 7 = SUT0 Fuse, 8 = SUT1 Fuse, 9 = CKDIV8 Fuse, A = CKOUT Fuse,
B = BODLEVEL0 Fuse, C = BODLEVEL1 Fuse, D= BODLEVEL2 Fuse, E = EESAVE Fuse, F = WDTON Fuse,
G = SPIEN Fuse, H = DWEN Fuse, I = RSTDISBL Fuse
Notes: 1. For page sizes less than 256 words, parts of the address (bbbb_bbbb) will be parts of the page address.
2. For page sizes less than 256 bytes, parts of the address (bbbb_bbbb) will be parts of the page address.
3. The EEPROM is written page-wise. But only the bytes that are loaded into the page are actually written to the
EEPROM. Page-wise EEPROM access is more efficient when multiple bytes are to be written to the same
page. Note that auto-erase of EEPROM is not available in High-voltage Serial Programming, only in SPI
Programming.
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29. Electrical Characteristics
29.1 Absolute Maximum Ratings
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 Min. Typ. Max. Unit
Automotive operating temperature – 40 +125 °C
Storage temperature – 65 +150 °C
Voltage on any pin except RESET
with respect to ground – 0.5 VCC + 0.5 V
Voltage on RESET with respect to ground – 0.5 +13.0 V
Voltage on VCC with respect to ground – 0.5 +6.0 V
DC current per I/O pin 40.0 mA
DC current VCC and GND pins 200.0 mA
Injection current at VCC = 0V to 5V(2) ±5.0 mA(1)
Notes: 1. Maximum current per port = ±30mA
2. Functional corruption may occur.
29.2 DC Characteristics
TA = –40°C to 125°C, VCC = 2.7V to 5.5V (unless otherwise noted)(1)
Parameter Condition Symbol Min. Typ. Max. Unit
Input low voltage VCC = 2.4V - 5.5V VIL –0.5 0.3VCC V
Input high-voltage
Except RESET pin VCC = 2.4V - 5.5V VIH –0.6VCC(3) VCC + 0.5(2) V
Input high-voltage
RESET pin VIH2 –0.9VCC(3) VCC + 0.5(2) V
Output low voltage(4)
(port B,PORTA)
IOL = 10mA, VCC = 5V
IOL = 5mA, VCC = 3V VOL
0.8
0.5
V
V
Output high-voltage(5)
(Port B2:0,PORTA)
IOH = –10mA, VCC = 5V
IOH = –5mA, VCC = 3V VOH
–4.3
–2.5
V
V
Input leakage
current I/O pin
Vcc = 5.5V, pin low
(absolute value) IILPORTA 50 nA
Notes: 1. All DC characteristics contained in this data sheet are based on actual silicon characterization of Atmel ATtiny24/44/84
AVR microcontrollers manufactured in corner run process technology. These values are preliminary values represent-
ing design targets, and will be updated after characterization of actual Automotive silicon.
2. “Max” means the highest value where the pin is guaranteed to be read as low.
3. “Min” means the lowest value where the pin is guaranteed to be read as high.
4. Although each I/O port can sink more than the test conditions (10mA at VCC = 5V, 5mA at VCC = 3V) under steady state
conditions (non-transient), the following must be observed:
1] The sum of all IOL, for all ports, should not exceed 60mA.
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.
5. Although each I/O port can source more than the test conditions (10mA at VCC = 5V, 5mA at VCC = 3V) under steady
state conditions (non-transient), the following must be observed:
1] The sum of all IOH, for all ports, should not exceed 60mA.
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. Pull up driving strength of the PB3 RESET pad is weak.
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Input leakage
current I/O pin
Vcc = 5.5V, pin high
(absolute value) IIHPORTA 50 nA
Input leakage
current I/O pin
Vcc = 5.5V, pin low
(absolute value) IIHPORTB <0.05 1µA
Input leakage
current I/O lin
Vcc = 5.5V, pin high
(absolute value) IILPORTB <0.05 1µA
Reset pull-up resistor RRST 30 60 kW
I/O pin pull-up resistor Rpu 20 50 kW
Power supply current
Active 1MHz, VCC = 3V
ICC
0.4 1.5 mA
Active 4MHz, VCC = 3V 1.8 3.0 mA
Active 8MHz, VCC = 5V 5.0 10.0 mA
Idle 1MHz, VCC = 3V 0.075 0.2 mA
Idle 4MHz, VCC = 3V 0.3 0.5 mA
Idle 8MHz, VCC = 5V 1.2 2.5 mA
Power-down mode
WDT enabled, VCC = 3V 5.0 30 µA
WDT enabled, VCC = 5V 9.0 50 µA
WDT disabled, VCC = 3V 2.5 24 µA
WDT disabled, VCC = 5V 4.3 36 µA
Analog comparator input
leakage current
VCC = 5V
Vin = VCC/2 IACLK –50 50 nA
29.2 DC Characteristics (Continued)
TA = –40°C to 125°C, VCC = 2.7V to 5.5V (unless otherwise noted)(1)
Parameter Condition Symbol Min. Typ. Max. Unit
Notes: 1. All DC characteristics contained in this data sheet are based on actual silicon characterization of Atmel ATtiny24/44/84
AVR microcontrollers manufactured in corner run process technology. These values are preliminary values represent-
ing design targets, and will be updated after characterization of actual Automotive silicon.
2. “Max” means the highest value where the pin is guaranteed to be read as low.
3. “Min” means the lowest value where the pin is guaranteed to be read as high.
4. Although each I/O port can sink more than the test conditions (10mA at VCC = 5V, 5mA at VCC = 3V) under steady state
conditions (non-transient), the following must be observed:
1] The sum of all IOL, for all ports, should not exceed 60mA.
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.
5. Although each I/O port can source more than the test conditions (10mA at VCC = 5V, 5mA at VCC = 3V) under steady
state conditions (non-transient), the following must be observed:
1] The sum of all IOH, for all ports, should not exceed 60mA.
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. Pull up driving strength of the PB3 RESET pad is weak.
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29.3 Speed Grades
Figure 29-1. Maximum Frequency versus VCC
29.4 Clock Characterizations
29.4.1 Calibrated Internal RC Oscillator Accuracy
Example: with oscillator divided by 32, jitter standard deviation will be 32 × 0.4ns = 12.8ns.
29.4.2 External Clock Drive Waveforms
Figure 29-2. External Clock Drive Waveforms
16MHz
8MHz
2.7V 4.5V 5.5V
Safe Operating
Area
Table 29-1. Calibration Accuracy of Internal RC Oscillator
Frequency VCC Temperature Accuracy
Factory
calibration 8.0MHz 3V 25°C ±2%
User calibration 7.3 - 8.1MHz 2.7V - 5.5V –40°C - 125°C ±20%
Oscillator jitter 8.0MHz 2.7V - 5.5V –40°C - 125° Standard deviation 0.4ns(1)
Note: 1. The overall jitter increase proportionally to the divider ratio
tCHCX
VIH1
VIL1
tCHCX
tCLCH tCHCL
tCLCX
tCLCL
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29.4.3 External Clock Drive
29.5 System and Reset Characterizations
Table 29-2. External Clock Drive
Parameter Symbol
VCC = 2.7 - 5.5V VCC = 4.5 - 5.5V
UnitMin. Max. Min. Max.
Clock frequency 1/tCLCL 010 020 MHz
Clock period tCLCL 100 50 ns
High time tCHCX 40 20 ns
Low time tCLCX 40 20 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 %
Table 29-3. Reset, Brown-out and Internal Voltage Reference Characteristics(1)
Parameter Symbol Condition Min Typ Max Unit
Brown-out detector hysteresis VHYST 100 250 mV
RAM retention voltage(1) VRAM2. 50 mV
Min Pulse width on brown-out reset tBOD 2ns
Bandgap reference voltage VBG VC C= 2.7V, TA = 25°C 1.0 1.1 1.2 V
Bandgap reference start-up time tBG VC C= 2.7V, TA = 25°C 40 70 µs
Bandgap reference current consumption IBG VC C= 2.7V, TA = 25°C 10 µA
Notes: 1. Values are guidelines only.
2. This is the limit to which VDD can be lowered without losing RAM data
Table 29-4. BODLEVEL Fuse Coding(1)
BODLEVEL [2..0] Fuses Min VBOT Typ VBOT Max VBOT Unit
111 BOD Disabled
110 1.8
V
101 2.7
100 4.3
011 2.3
010 2.2
001 1.9
000 2.0
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.
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29.6 ADC Characteristics – Preliminary Data
Table 29-5. ADC Characteristics, Single Ended Channels. –40°C - 125°C
Parameter Condition Symbol Min Typ Max Unit
Resolution Single ended conversion 10 Bits
Absolute accuracy (including
INL, DNL, quantization error,
gain and offset error)
Single ended conversion
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
TUE
2.0 4.0 LSB
Single ended conversion
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
Noise reduction mode
2.0 4.0 LSB
Integral non-linearity (INL)
Single ended conversion
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
INL 0.5 1.5 LSB
Differential non-linearity (DNL)
Single ended conversion
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
DNL 0.3 0.7 LSB
Gain error
Single ended conversion
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
–5.0 –3.0 5.0 LSB
Offset error
Single ended conversion
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
–3.5 1.5 3.5 LSB
Conversion time Free running conversion 65 260 µs
Clock frequency 50 200 kHz
External voltage reference Vref 2.56 AVCC V
Input voltage VIN GND VREF V
Internal voltage reference VINT 1.0 1.1 1.2 V
Analog input resistance RAIN 100 MΩ
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Table 29-6. ADC Characteristics, Differential Channels, TA = –40°C to 125°C
Parameter Condition Symbol Min Typ Max Unit
Resolution Gain = 1x 8Bits
Gain = 20x 8Bits
Absolute accuracy
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200kHz TUE
2.5 5.0 LSB
Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200kHz
3.0 6.0 LSB
Integral non-linearity (INL)
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200kHz
0.5 2.5 LSB
Bipolar - Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200kHz
INL 0.5 3.0 LSB
Unipolar - Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200kHz
1.5 5.0 LSB
Differential non-linearity (DNL)
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200kHz
0.4 1.0 LSB
Bipolar - Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200kHz
DNL 0.4 1.0 LSB
Unipolar - Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200kHz
0.7 2.0 LSB
Gain error
Bipolar -Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200kHz
–5.0 2.3 5.0 LSB
Unipolar -Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200kHz
–5.0 –2.8 5.0 LSB
Bipolar -Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200kHz
–7.0 2.2 7.0 LSB
Unipolar -Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200kHz
–7.0 -1.8 7.0 LSB
Offset error
Gain = 1x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200kHz
–5.0 2.0 5.0 LSB
Bipolar - Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200kHz
–5.0 2.0 5.0 LSB
Unipolar - Gain = 20x
VREF = 4V, VCC = 5V
ADC clock = 50 - 200kHz
–6.5 2.0 6.5 LSB
181
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29.7 Serial Programming Characteristics
Figure 29-3. Serial Programming Timing
Figure 29-4. Serial Programming Waveforms
Clock frequency 50 200 kHz
Conversion time 65 260 µs
Reference voltage VREF 2.56 AVCC - 0.5 V
Input voltage VIN GND AVCC V
Input differential voltage VDIFF –VREF/gain VREF/gain V
Table 29-6. ADC Characteristics, Differential Channels, TA = –40°C to 125°C (Continued)
Parameter Condition Symbol Min Typ Max Unit
MOSI
SCK
MISO
tOVSH tSHOX
tSHSL
tSLSH
tSLIV
Serial Data Input
(MOSI)
Serial Data Output
(MISO)
Serial Clock Input
(SCK)
Sample
MSB LSB
MSB LSB
Table 29-7. Serial Programming Characteristics, TA = –40°C to 125°C, VCC = 2.7 to 5.5V (Unless Otherwise Noted)
Parameter Symbol Min Typ Max Unit
Oscillator frequency (ATtiny24/44/84V) 1/tCLCL 0 4 MHz
Oscillator period (ATtiny24/44/84V) tCLCL 250 ns
Oscillator frequency (ATtiny24/44/84, VCC = 4.5V - 5.5V) 1/tCLCL 020 MHz
Oscillator period (ATtiny24/44/84, VCC = 4.5V - 5.5V) tCLCL 50 ns
SCK pulse width high tSHSL 2 tCLCL* ns
SCK pulse width low tSLSH 2 tCLCL*ns
MOSI setup to SCK high tOVSH tCLCL ns
MOSI hold after SCK high tSHOX 2 tCLCL ns
SCK low to MISO valid tSLIV TBD TBD TBD ns
Note: 1. 2 tCLCL for fck < 12MHz, 3 tCLCL for fck ≥ 12MHz
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29.8 High-voltage Serial Programming Characteristics
Figure 29-5. High-voltage Serial Programming Timing
1 CK Cycle
VCC
RESET
Internal
Reset
RESET
Time-out
WDT
Time-out
tTOUT
Table 29-8. High-voltage Serial Programming Characteristics
TA = 25°C ±10%, VCC = 5.0V ±10% (Unless otherwise noted)
Parameter Symbol Min Typ Max Unit
SCI (PB0) pulse width high tSHSL 110 ns
SCI (PB0) pulse width low tSLSH 110 ns
SDI (PA6), SII (PB1) valid to SCI (PB0) high tIVSH 50 ns
SDI (PA6), SII (PB1) hold after SCI (PB0) high tSHIX 50 ns
SCI (PB0) high to SDO (PA4) valid tSHOV 16 ns
Wait after Instr. 3 for write fuse bits tWLWH_PFB 2.5 ms
183
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30. Typical Characteristics – Preliminary Data
The data contained in this section is largely based on simulations and characterization of similar devices in the same
process and design methods. Thus, the data should be treated as indications of how the part will behave.
The following charts show typical behavior. These figures are not tested during manufacturing. All current consumption
measurements are performed with all I/O pins configured as inputs and with internal pull-ups enabled. A sine wave generator
with rail-to-rail output is used as clock source.
The power consumption in power-down mode is independent of clock selection.
The current consumption is a function of several factors such as: operating voltage, operating frequency, loading of I/O pins,
switching rate of I/O pins, code executed and ambient temperature. The dominating factors are operating voltage and
frequency.
The current drawn from capacitive loaded pins may be estimated (for one pin) as CL × VCC × f where CL= load capacitance,
VCC = operating voltage and f = average switching frequency of I/O pin.
The parts are characterized at frequencies higher than test limits. Parts are not guaranteed to function properly at
frequencies higher than the ordering code indicates.
The difference between current consumption in power-down mode with watchdog timer enabled and power-down mode with
watchdog timer disabled represents the differential current drawn by the watchdog timer.
30.1 Active Supply Current
Figure 30-1. Active Supply Current versus Low Frequency (0.1 to 1.0MHz) - Temp. = 25°C
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
5.5V
5.0V
4.5V
3.3V
3.0V
2.7V
1
Frequency (MHz)
1.2
1
0.8
0.6
0.4
0.2
0
ICC (mA)
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Figure 30-2. Active Supply Current versus Low Frequency (0.1 to 1.0MHz) - Temp. = 125°C
Figure 30-3. Active Supply Current versus frequency (1 to 20MHz) - Temp. = 25°C
Figure 30-4. Active Supply Current versus frequency (1 to20MHz) - Temp. = 125°C
5.5V
5.0V
4.5V
3.3V
3.0V
2.7V
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Frequency (MHz)
1.2
1
0.8
0.6
0.4
0.2
0
ICC (mA)
5.5V
5.0V
4.5V
3.3V
3.0V
2.7V
0 2 4 6 8 10 12 14 16 18 20
Frequency (MHz)
25
20
15
10
5
0
ICC (mA)
5.5V
5.0V
4.5V
3.3V
3.0V
2.7V
0 2 4 6 8 101214161820
Frequency (MHz)
25
20
15
10
5
0
ICC (mA)
185
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Figure 30-5. Active Supply Current versus VCC (Internal RC Oscillator, 8MHz)
Figure 30-6. Active Supply Current versus VCC (Internal RC Oscillator, 1MHz)
Figure 30-7. Active Supply Current versus VCC (Internal RC Oscillator, 128kHz)
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
5
4
7
6
3
2
1
0
ICC (mA)
85°C
125°C
25°C
-45°C
85°C
125°C
25°C
-40°C
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
1
0.8
1.4
1.2
0.6
0.4
0.2
0
ICC (mA)
85°C
125°C
25°C
-40°C
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
0.2
0.16
0.12
0.08
0.04
0
ICC (mA)
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30.2 Idle Supply Current
Figure 30-8. Idle Supply Current versus Low Frequency (0.1 to 1.0MHz)
Figure 30-9. Idle Supply Current versus Frequency (1 to 20MHz)
5.5V
5.0V
4.5V
3.3V
3.0V
2.7V
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Frequency (MHz)
0.012
0.01
0.008
0.006
0.004
0.002
0
ICC (mA)
5.5V
5.0V
4.5V
3.3V
3.0V
2.7V
0 2 4 6 8 101214161820
Frequency (MHz)
2.5
2
1.5
4
3.5
3
1
0.5
0
ICC (mA)
187
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Figure 30-10. Idle Supply Current versus VCC (Internal RC Oscillator, 8MHz)
Figure 30-11. Idle Supply Current versus VCC (Internal RC Oscillator, 1MHz)
Figure 30-12. Idle Supply Current versus VCC (Internal RC Oscillator, 8MHz)
85°C
125°C
25°C
-40°C
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
1
0.8
1.4
1.2
1.6
2
1.8
0.6
0.4
0.2
0
ICC (mA)
85°C
125°C
25°C
-40°C
2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
0.25
0.2
0.35
0.3
0.15
0.1
0.05
0
I
CC
(mA)
85°C
125°C
25°C
-40°C
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
0.025
0.02
0.035
0.03
0.015
0.01
0.005
0
ICC (mA)
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30.3 Supply Current of IO modules
The tables and formulas below can be used to calculate the additional current consumption for the different I/O modules in
active and idle mode. The enabling or disabling of the I/O modules are controlled by the power reduction register. See
Section 15.6 “Power Reduction Register” on page 46 for details.
30.4 Power-down Supply Current
Figure 30-13. Power-down Supply Current versus VCC (Watchdog Timer Disabled)
Figure 30-14. Power-down Supply Current versus VCC (Watchdog Timer Enabled)
Table 30-1. Additional Current Consumption for the Different I/O Modules (Absolute Values)
PRR bit Typical numbers
VCC = 2V, F = 1MHz VCC = 3V, F = 4MHz VCC = 5V, F = 8MHz
PRTIM1 6.6µA 26µA 106µA
PRTIM0 8.7µA 35µA 140µA
PRUSI 5.5µA 22µA 87µA
PRADC 22µA 87µA 340µA
85°C
125°C
25°C
-45°C
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
2.5
2
3.5
3
4
5
4.5
1.5
1
0.5
0
ICC (µA)
85°C
125°C
25°C
-45°C
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
5
4
7
6
8
10
9
3
2
1
0
ICC (µA)
189
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30.5 Pin Pull-up
Figure 30-15. I/O Pin Pull-up Resistor Current versus input Voltage (VCC = 2.7V)
Figure 30-16. I/O pin Pull-up Resistor Current versus Input Voltage (VCC = 5V)
85°C
125°C
25°C
-45°C
0 0.5 1 1.5 2 2.5 3
VOP (V)
50
40
70
60
80
90
30
20
10
0
IOP (µA)
85°C
125°C
25°C
-45°C
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
VOP (V)
100
80
140
120
160
60
40
20
0
IOP (µA)
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Figure 30-17. Reset Pull-up Resistor Current versus Reset Pin Voltage (VCC = 2.7V)
Figure 30-18. Reset Pull-up Resistor Current versus Reset Pin Voltage (VCC = 5V)
-40°C
125°C
0 0.5 1 1.5 2 2.5 3
V
RESET
(V)
50
40
60
30
20
10
0
I
RESET
(µA)
-40°C
125°C
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
VRESET (V)
100
80
120
60
40
20
0
IRESET (µA)
191
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30.6 Pin Driver Strength
Figure 30-19. I/O Pin Output Voltage versus Sink Current (VCC = 3V)
Figure 30-20. I/O Pin Output Voltage versus Sink Current (VCC = 5V)
85°C
125°C
25°C
-40°C
0 2 4 6 8 101214161820
IOL (mA)
0.04
0.03
0.06
0.05
0.02
0.01
0
VOL (V)
85°C
125°C
25°C
-45°C
02468101214161820
IOL (mA)
0.4
0.3
0.6
0.7
0.5
0.2
0.1
0
VOL (V)
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Figure 30-21. I/O Pin Output Voltage versus Source Current (VCC = 3V)
Figure 30-22. I/O Pin output Voltage versus Source Current (VCC = 5V)
85°C
125°C
25°C
-45°C
0 2 4 6 8 10 12 14 16 18 20
IOH (mA)
2.5
3.5
3
2
1.5
VOH (V)
85°C
125°C
25°C
-45°C
0 2 4 6 8 10 12 14 16 18 20
I
OH
(mA)
4.5
4.7
4.6
4.4
4.9
5.1
5
4.8
4.3
V
OH
(V)
193
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30.7 Pin Threshold and Hysteresis
Figure 30-23. I/O Pin Input Threshold Voltage versus VCC (VIH, IO Pin Read as ‘1’)
Figure 30-24. I/O Pin Input threshold Voltage versus VCC (VIL, IO Pin Read as ‘0’)
85°C
125°C
25°C
-40°C
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
1
2
1.5
2.5
3.5
3
0.5
0
Threshold (V)
85°C
125°C
25°C
-40°C
2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
1
2
1.5
2.5
0.5
0
Threshold (V)
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Figure 30-25. I/O Pin Input Hysteresis versus VCC
Figure 30-26. Reset Input Threshold Voltage versus VCC (VIH, IO Pin Threshold as ‘1’)
Figure 30-27. Reset Input Threshold Voltage versus VCC (VIL, IO Pin Read as ‘0’)
85°C
125°C
-20°C
-40°C
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
0.1
0.2
0.15
0.25
0.05
0.35
0.45
0.4
0.5
0.3
0
Input Hysteresis (mV)
85°C
125°C
25°C
-40°C
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
1
2
1.5
2.5
0.5
3
0
Threshold (V)
85°C
125°C
25°C
-45°C
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
1
2
1.5
2.5
0.5
3
0
Threshold (V)
195
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Figure 30-28. Reset Pin Input Hysteresis versus VCC
30.8 BOD Threshold and Analog Comparator Offset
Figure 30-29. BOD Threshold versus Temperature (BODLEVEL is 4.3V)
85°C
125°C
25°C
-40°C
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
0.2
0.4
0.3
0.5
0.1
0.7
0.9
0.8
1
0.6
0
Input Hysteresis (mV)
1
0
-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
Temperature (°C)
4.25
4.35
4.3
4.4
4.2
4.15
Threshold (V)
100 110 120
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Figure 30-30. BOD Threshold versus Temperature (BODLEVEL is 2.7V)
Figure 30-31. BOD Threshold versus Temperature (BODLEVEL is 1.8V)
1
0
2.68
2.72
2.70
2.74
2.76
2.78
2.66
2.64
Threshold (V)
-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
Temperature (°C)
100 110 120
1
0
1.80
1.82
1.81
1.83
1.84
1.85
1.79
1.78
Threshold (V)
-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
Temperature (°C)
100 110 120
197
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30.9 Internal Oscillator Speed
Figure 30-32. Watchdog Oscillator Frequency versus VCC
Figure 30-33. Calibrated 8MHz RC Oscillator Frequency versus VCC
85°C
125°C
25°C
-40°C
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
114
112
118
116
120
124
122
110
108
106
104
FRC (kHz)
85°C
125°C
25°C
-40°C
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
8.5
8
9
7.5
7
6.5
6
FRC (MHz)
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Figure 30-34. Calibrated 8MHz RC oscillator Frequency versus Temperature
Figure 30-35. Calibrated 8MHz RC Oscillator Frequency versus OSCCAL Value
5.0V
3.0V
7.9
8.1
8
8.2
8.3
8.4
7.8
7.7
F
RC
(MHz)
-40-30-20-10 0 102030405060708090
Temperature (°C)
100 110 120
4
8
6
10
12
14
16
2
0
FRC (MHz)
0 16 32 48 64 80 96 112 128 144 160 176 192 208
OSCCAL (X1)
224 240 256
85°C
125°C
25°C
-40°C
199
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30.10 Current Consumption of Peripheral Units
Figure 30-36. ADC Current versus VCC
Figure 30-37. AREF External Reference Current versus VCC
200
400
300
500
600
700
100
0
ICC (µA)
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
85°C
125°C
25°C
-40°C
4
8
6
10
12
14
2
0
AREF Pin Current (µA)
1.5 2 2.5 3 3.5 4 4.5 5 5.5
AREF (V)
25°C
ATA8741 [DATASHEET]
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200
Figure 30-38. Analog Comparator Current versus VCC
Figure 30-39. Programming Current versus VCC
Figure 30-40. Brownout Detector Current versus VCC
20
40
30
50
60
70
80
90
100
10
0
ICC (µA)
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
85°C
125°C
25°C
-40°C
4000
8000
6000
10000
12000
2000
0
ICC (µA)
2.5 3.5 4.5 5.5
VCC (V)
25°C
1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5
VCC (V)
10
8
6
16
14
12
4
2
0
ICC (µA)
85°C
125°C
25°C
-40°C
201
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Figure 30-41. Watchdog Timer Current versus VCC
30.11 Current Consumption in Reset and Reset Pulse Width
Figure 30-42. Reset Supply Current versus VCC (0.1 to 1.0MHz, excluding Current Through the Reset Pull-up)
85°C
125°C
25°C
-40°C
2.5 3 3.5 4 4.5 5 5.5
VCC (V)
25
20
30
15
10
5
0
ICC (µA)
5.5V
5.0V
4.5V
3.3V
3.0V
2.7V
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Frequency (MHz)
0.12
0.1
0.08
0.06
0.2
0.18
0.16
0.14
0.04
0.02
0
ICC (mA)
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Figure 30-43. Reset Supply Current versus VCC (1 to 20MHz, Excluding Current Through the Reset Pull-up)
Figure 30-44. Minimum Reset Pulse Width versus VCC
5.5V
5.0V
4.5V
3.3V
3.6V
3.0V
2.7V
0 2 4 6 8 10 12 14 16 18 20
Frequency (MHz)
3
2.5
2
1.5
1
0.5
0
ICC (mA)
85°C
125°C
25°C
-40°C
2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
1000
800
1200
600
400
200
0
Pulse width (ns)
203
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31. Register Summary
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
0x3F (0x5F) SREG I T H S V N Z C 22
0x3E (0x5E) SPH –––––– SP9 SP8 25
0x3D (0x5D) SPL SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 25
0x3C (0x5C) OCR0B Timer/Counter0 – Output Compare Register B 92
0x3B (0x5B) GIMSK – INT0 PCIE1 PCIE0 – – – – 62
0x3A (0x5A GIFR – INTF0 PCIF1 PCIF0 – – – – 63
0x39 (0x59) TIMSK0 – – – – – OCIE0B OCIE0A TOIE0 92
0x38 (0x58) TIFR0 – – – – –OCF0BOCF0ATOV0 93
0x37 (0x57) SPMCSR – – – CTPB RFLB PGWRT PGERS SPMEN 160
0x36 (0x56) OCR0A Timer/Counter0 – Output Compare Register A 92
0x35 (0x55) MCUCR – PUD SE SM1 SM0 –ISC01ISC00 62
0x34 (0x54) MCUSR – – – – WDRF BORF EXTRF PORF 55
0x33 (0x53) TCCR0B FOC0A FOC0B –– WGM02 CS02 CS01 CS00 91
0x32 (0x52) TCNT0 Timer/Counter0 92
0x31 (0x51) OSCCAL CAL7 CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 43
0x30 (0x50) TCCR0A COM0A1 COM0A0 COM0B1 COM0B0 ––WGM01WGM00 88
0x2F (0x4F) TCCR1A COM1A1 COM1A0 COM1B1 COM1B0 ––WGM11WGM10 114
0x2E (0x4E) TCCR1B ICNC1 ICES1 – WGM13 WGM12 CS12 CS11 CS10 116
0x2D (0x4D) TCNT1H Timer/Counter1 – Counter Register High Byte 117
0x2C (0x4C) TCNT1L Timer/Counter1 – Counter Register Low Byte 117
0x2B (0x4B) OCR1AH Timer/Counter1 – Compare Register A High Byte 117
0x2A (0x4A) OCR1AL Timer/Counter1 – Compare Register A Low Byte 117
0x29 (0x49) OCR1BH Timer/Counter1 – Compare Register B High Byte 118
0x28 (0x48) OCR1BL Timer/Counter1 – Compare Register B Low Byte 118
0x27 (0x47) DWDR DWDR[7:0] 156
0x26 (0x46) CLKPR CLKPCE – – – CLKPS3 CLKPS2 CLKPS1 CLKPS0 43
0x25 (0x45) ICR1H Timer/Counter1 - Input Capture Register High Byte 118
0x24 (0x44) ICR1L Timer/Counter1 - Input Capture Register Low Byte 118
0x23 (0x43) GTCCR TSM –––––– PSR10 121
0x22 (0x42) TCCR1C FOC1A FOC1B – – – – – – 117
0x21 (0x41) WDTCSR WDIF WDIE WDP3 WDCE WDE WDP2 WDP1 WDP0 56
0x20 (0x40) PCMSK1 – – – – PCINT11 PCINT10 PCINT9 PCINT8 63
0x1F (0x3F) EEARH – – – – – – – EEAR8 34
0x1E (0x3E) EEARL EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 34
0x1D (0x3D) EEDR EEPROM Data Register 35
0x1C (0x3C) EECR –– EEPM1 EEPM0 EERIE EEMPE EEPE EERE 35
0x1B (0x3B) PORTA PORTA7 PORTA6 PORTA5 PORTA4 PORTA3 PORTA2 PORTA1 PORTA0 76
0x1A (0x3A) DDRA DDA7 DDA6 DDA5 DDA4 DDA3 DDA2 DDA1 DDA0 77
0x19 (0x39) PINA PINA7 PINA6 PINA5 PINA4 PINA3 PINA2 PINA1 PINA0 77
0x18 (0x38) PORTB – – – – PORTB3 PORTB2 PORTB1 PORTB0 77
0x17 (0x37) DDRB – – – – DDB3 DDB2 DDB1 DDB0 77
0x16 (0x36) PINB – – – – PINB3 PINB2 PINB1 PINB0 77
Note: 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 AVR®, the CBI and
SBI instructions will only operation 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.
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0x15 (0x35) GPIOR2 General Purpose I/O Register 2 36
0x14 (0x34) GPIOR1 General Purpose I/O Register 1 36
0x13 (0x33) GPIOR0 General Purpose I/O Register 0 36
0x12 (0x32) PCMSK0 PCINT7 PCINT6 PCINT5 PCINT4 PCINT3 PCINT2 PCINT1 PCINT0 63
0x11 (0x31)) Reserved –
0x10 (0x30) USIBR USI Buffer Register 128
0x0F (0x2F) USIDR USI Data Register 128
0x0E (0x2E) USISR USISIF USIOIF USIPF USIDC USICNT3 USICNT2 USICNT1 USICNT0 129
0x0D (0x2D) USICR USISIE USIOIE USIWM1 USIWM0 USICS1 USICS0 USICLK USITC 130
0x0C (0x2C) TIMSK1 ––ICIE1–– OCIE1B OCIE1A TOIE1 118
0x0B (0x2B) TIFR1 ––ICF1––OCF1BOCF1ATOV1 119
0x0A (0x2A) Reserved –
0x09 (0x29) Reserved –
0x08 (0x28) ACSR ACD ACBG ACO ACI ACIE ACIC ACIS1 ACIS0 134
0x07 (0x27) ADMUX REFS1 REFS0 MUX5 MUX4 MUX3 MUX2 MUX1 MUX0 149
0x06 (0x26) ADCSRA ADEN ADSC ADATE ADIF ADIE ADPS2 ADPS1 ADPS0 152
0x05 (0x25) ADCH ADC Data Register High Byte 153
0x04 (0x24) ADCL ADC Data Register Low Byte 153
0x03 (0x23) ADCSRB BIN ACME –ADLAR– ADTS2 ADTS1 ADTS0 153
0x02 (0x22) Reserved –
0x01 (0x21) DIDR0 ADC7D ADC6D ADC5D ADC4D ADC3D ADC2D ADC1D ADC0D 135,154
0x00 (0x20) PRR – – – – PRTIM1 PRTIM0 PRUSI PRADC 46
31. Register Summary (Continued)
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
Note: 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 AVR®, the CBI and
SBI instructions will only operation 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.
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32. 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
Branch Instructions
RJMP kRelative jump PC ← PC + k + 1 None 2
IJMP Indirect jump to (Z) PC ← Z None 2
RCALL kRelative subroutine call PC ← PC + k + 1 None 3
ICALL Indirect call to (Z) PC ← Z None 3
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
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
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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
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
32. Instruction Set Summary (Continued)
Mnemonics Operands Description Operation Flags #Clocks
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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
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
32. Instruction Set Summary (Continued)
Mnemonics Operands Description Operation Flags #Clocks
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Appendix 2: Appendix B - ATA8741/ATA8742/ATA8743 Automotive Specification at 1.8V
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33. Description
This document contains information specific to devices operating at voltage between 1.8V and 3.6V. Only deviations with
standard operating characteristics are covered in this appendix, all other information can be found in the complete
Automotive datasheet. The complete Atmel® ATtiny24/ATtiny44/ATtiny84 automotive datasheet can be found on
http://www.atmel.com.
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34. Electrical Characteristics
34.1 Absolute Maximum Ratings
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 Value Unit
Operating temperature –40 to +85 °C
Storage temperature –65 to +175 °C
Voltage on any pin except RESET with respect to ground –0.5 to VCC + 0.5 V
Maximum operating voltage 6.0 V
DC current per I/O pin 30.0 mA
DC current VCC and GND pins 200.0 mA
34.2 DC Characteristics
TA = –40°C to +85°C, VCC = 1.8V to 3.6V (unless otherwise noted)
Parameters Condition Symbol Min. Typ. Max. Unit
Input low voltage, except XTAL1
and RESET pin VCC = 1.8V to 3.6V VIL –0.5 +0.2VCC(1) V
Input high voltage, except XTAL1
and RESET pins VCC = 1.8V to 3.6V VIH 0.7VCC(2) VCC + 0.5 V
Input low voltage, XTAL1 pin VCC = 1.8V to 3.6V VIL1 –0.5 +0.2VCC(1) V
Input high voltage, XTAL1 pin VCC = 1.8V to 3.6V VIH1 0.9VCC(2) VCC + 0.5 V
Input low voltage, RESET pin VCC = 1.8V to 3.6V VIL2 –0.5 +0.2VCC(1) V
Input high voltage, RESET pin VCC = 1.8V to 3.6V VIH2 0.9VCC(2) VCC + 0.5 V
Output low voltage(3),
I/O pin except RESET IOL = 2mA, VCC = 1.8V VOL 0.2 V
Output high voltage(4),
I/O pin except RESET IOH = –2mA, VCC = 1.8V VOH 1.2 V
Power supply current Active 4MHz, VCC = 3V
ICC
0.8 2.5 mA
Idle 4MHz, VCC = 3V 0.2 0.5 mA
Power-down mode WDT disabled, VCC = 3V
WDT enabled, VCC = 3V
0.2
4
24
30 µA
Analog comparator
input offset voltage
VCC = 2.7V
Vin = VCC/2 VACIO <10 40 mV
Analog comparator
input leakage current
VCC = 2.7V
Vin = VCC/2 IACLK –50 +50 nA
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 (2mA at VCC = 1.8V) under steady state conditions (non-
transient), the following must be observed: (1) The sum of all IOL, for all ports, should not exceed 50mA. 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 (0.5mA at VCC = 1.8V) under steady state conditions
(nontransient), the following must be observed: (1) The sum of all IOL, for ports B0 to B5, should not exceed 50mA. 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.
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34.3 Maximum Speed versus VCC
Maximum frequency is dependent on VCC. As shown in Figure 34-1, the maximum frequency versus VCC curve is linear
between 1.8V < VCC < 3.6V.
Figure 34-1. Maximum Frequency versus VCC
34.4 Clock Characterizations
8MHz
1.8V 2.7V 3.6V
4MHz
Safe Operating Area
Table 34-1. Calibration Accuracy of Internal RC Oscillator
Frequency VCC Temperature Accuracy
User calibration 7.3MHz to 8.1MHz 1.8V to 3.6V –40°C to +85°C ±25%
34.5 ADC Characteristics
TA = –40°C to +85°C, VCC = 1.8V to 3.6V (unless otherwise noted)
Parameters Test Conditions Symbol Min. Typ. Max. Unit
Resolution Single ended conversion 10 Bits
Absolute accuracy (Including INL,
DNL, quantization error, gain and
offset error)
VCC = 1.8V, VRef = 1.8V,
ADC clock = 200 kHz 24.0 LSB
VCC = 1.8V, VRef = 1.8V,
ADC clock = 200 kHz
Noise Reduction Mode
24.0 LSB
Integral non-linearity (INL) VCC = 1.8V, VRef = 1.8V,
ADC clock = 200 kHz 0.5 1.5 LSB
Differential non-linearity (DNL) VCC = 1.8V, VRef = 1.8V,
ADC clock = 200 kHz 0.2 0.7 LSB
Gain error VCC = 1.8V, VRef = 1.8V,
ADC clock = 200 kHz –7.0 –3.0 +5.0 LSB
Offset error VCC = 1.8V, VRef = 1.8V,
ADC clock = 200 kHz –3.5 +1.5 +3.5 LSB
Reference voltage VREF 1.8 AVCC V
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34.6 ADC Characteristics
TA = –40°C to +85°C, VCC = 1.8V to 3.6V (unless otherwise noted)
Parameters Test Conditions Symbol Min. Typ. Max. Unit
Resolution Differential conversion, gain = 1x
BIPOLAR mode only 8Bits
Absolute accuracy (Including INL,
DNL, quantization error, gain and
offset error)
Gain = 1x, VCC = 1.8V, VRef =1.3V,
ADC clock = 125kHz 1.6 5.0 LSB
Integral non-linearity (INL)
Gain = 1x, VCC = 1.8V,
VRef = 1.3V,
ADC clock = 125kHz
0.7 2.5 LSB
Differential non-linearity (DNL)
Gain = 1x, VCC = 1.8V,
VRef = 1.3V,
ADC clock = 125kHz
0.3 1.0 LSB
Gain error
Gain = 1x, VCC = 1.8V,
VRef = 1.3V,
ADC clock = 125kHz
–7.0 +1.50 +7.0 LSB
Offset error
Gain = 1x, VCC = 1.8V.
VRef = 1.3V,
ADC clock = 125kHz
–4.0 0.0 +4.0 LSB
Reference voltage VREF 1.30 AVCC –
0.5 V
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36. Package Information
35. Ordering Information
Extended Type Number Package Remarks
ATA8741C-PXQW-1 QFN24 5mm × 5mm Microcontroller with UHF Tx for 310MHz to 350MHz, MOQ 6000
Package Drawing Contact:
packagedrawings@atmel.com
GPC DRAWING NO.
REV. TITLE
6.543-5132.02-4 1
10/18/13
Package: VQFN_5x5_24L
Exposed pad 3.6x3.6
COMMON DIMENSIONS
(Unit of Measure = mm)
MIN NOM NOTEMAXSymbol
Dimensions in mm
specifications
according to DIN
technical drawings
0.035 0.050.0A1
55.14.9E
0.25 0.30.2b
0.65e
0.4 0.450.35L
3.6 3.73.5E2
3.6 3.73.5D2
55.14.9D
0.21 0.260.16A3
0.85 0.90.8A
Top View
D
24
1
6
PIN 1 ID
E
Side View
A3
A
A1
b
L
Z 10:1
Bottom View
e
D2
24 19
7
1
6
12
13
18
E2
Z
ATA8741 [DATASHEET]
9140E–INDCO–09/14
214
37. 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
9140E-INDCO-09/14 • Section 35 “Ordering Information” on page 214 updated
• Section 36 “Package Information” on page 214 updated
9140D-INDCO-05/14 • Put datasheet in the latest template
9140C-INDCO-02/10 • Section 35 “Ordering Information” on page 237 changed
X
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