Features
•High Performance, Low Power Atmel®AVR® 8-Bit Microcontroller
•Advanced RISC Architecture
– 130 Powerful Instructions – Most Single Clock Cycle Execution
– 32 x 8 General Purpose Working Registers
– Fully Static Operation
– Up to 16 MIPS Throughput at 16MHz
– On-Chip 2-cycle Multiplier
•High Endurance Non-volatile Memory Segments
– In-System Self-programmable Flash Program Memory
• 32KBytes (ATmega329/ATmega3290)
• 64KBytes (ATmega649/ATmega6490)
– EEPROM
• 1Kbytes (ATmega329/ATmega3290)
• 2Kbytes (ATmega649/ATmega6490)
– Internal SRAM
• 2Kbytes (ATmega329/ATmega3290)
• 4Kbytes (ATmega649/ATmega6490)
– Write/Erase Cycles: 10,000 Flash/ 100,000 EEPROM
– Data retention: 20 years at 85°C/100 years at 25°C(1)
– Optional Boot Code Section with Independent Lock Bits
• In-System Programming by On-chip Boot Program
• True Read-While-Write Operation
– Programming Lock for Software Security
•JTAG (IEEE std. 1149.1 compliant) Interface
– Boundary-scan Capabilities According to the JTAG Standard
– Extensive On-chip Debug Support
– Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG Interface
•Peripheral Features
– 4 x 25 Segment LCD Driver (ATmega329/ATmega649)
– 4 x 40 Segment LCD Driver (ATmega3290/ATmega6490)
– Two 8-bit Timer/Counters with Separate Prescaler and Compare Mode
– One 16-bit Timer/Counter with Separate Prescaler, Compare Mode, and Capture
Mode
– Real Time Counter with Separate Oscillator
–Four PWM Channels
– 8-channel, 10-bit ADC
– Programmable Serial USART
– Master/Slave SPI Serial Interface
– Universal Serial Interface with Start Condition Detector
– Programmable Watchdog Timer with Separate On-chip Oscillator
– On-chip Analog Comparator
– Interrupt and Wake-up on Pin Change
•Special Microcontroller Features
– Power-on Reset and Programmable Brown-out Detection
– Internal Calibrated Oscillator
– External and Internal Interrupt Sources
– Five Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, and
Standby
•I/O and Packages
– 53/68 Programmable I/O Lines
– 64-lead TQFP, 64-pad QFN/MLF, and 100-lead TQFP
•Speed Grade:
– ATmega329V/ATmega3290V/ATmega649V/ATmega6490V:
– 0 - 4MHz @ 1.8 - 5.5V, 0 - 8MHz @ 2.7 - 5.5V
– ATmega329/3290/649/6490:
– 0 - 8MHz @ 2.7 - 5.5V, 0 - 16MHz @ 4.5 - 5.5V
•Temperature range:
– -40°C to 85°C Industrial
•Ultra-Low Power Consumption
– Active Mode:
• 1MHz, 1.8V: 350µA
• 32kHz, 1.8V: 20µA (including Oscillator)
• 32kHz, 1.8V: 40µA (including Oscillator and LCD)
– Power-down Mode:
• 100nA at 1.8V
8-bit Atmel
Microcontroller
with In-System
Programmable
Flash
ATmega329/V
ATmega3290/V
ATmega649/V
ATmega6490/V
2552K–AVR–04/11
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2552K–AVR–04/11
ATmega329/3290/649/6490
1. Pin Configurations
Figure 1-1. Pinout ATmega3290/6490
(OC2A/PCINT15) PB7
DNC
(T1/SEG33) PG3
(T0/SEG32) PG4
RESET/PG5
VCC
GND
(TOSC2) XTAL2
(TOSC1) XTAL1
DNC
DNC
(PCINT26/SEG31) PJ2
(PCINT27/SEG30) PJ3
(PCINT28/SEG29) PJ4
(PCINT29/SEG28) PJ5
(PCINT30/SEG27) PJ6
DNC
(ICP1/SEG26) PD0
(INT0/SEG25) PD1
(SEG24) PD2
(SEG23) PD3
(SEG22) PD4
(SEG21) PD5
(SEG20) PD6
(SEG19) PD7
AVCC
AGND
AREF
PF0 (ADC0)
PF1 (ADC1)
PF2 (ADC2)
PF3 (ADC3)
PF4 (ADC4/TCK)
PF5 (ADC5/TMS)
PF6 (ADC6/TDO)
PF7 (ADC7/TDI)
DNC
DNC
PH7 (PCINT23/SEG36)
PH6 (PCINT22/SEG37)
PH5 (PCINT21/SEG38)
PH4 (PCINT20/SEG39)
DNC
DNC
GND
VCC
DNC
PA0 (COM0)
PA1 (COM1)
PA2 (COM2)
PA3 (COM3)
PA4 (SEG0)
PA5 (SEG1)
PA6 (SEG2)
PA7 (SEG3)
PG2 (SEG4)
PC7 (SEG5)
PC6 (SEG6)
DNC
PH3 (PCINT19/SEG7)
PH2 (PCINT18/SEG8)
PH1 (PCINT17/SEG9)
PH0 (PCINT16/SEG10)
DNC
DNC
DNC
DNC
PC5 (SEG11)
PC4 (SEG12)
PC3 (SEG13)
PC2 (SEG14)
PC1 (SEG15)
PC0 (SEG16)
PG1 (SEG17)
PG0 (SEG18)
INDEX CORNER
ATmega3290/6490
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
75
74
73
72
71
70
69
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
51
100
99
98
97
96
95
94
93
92
91
90
89
88
87
86
85
84
83
82
81
80
79
78
77
76
LCDCAP
(RXD/PCINT0) PE0
(TXD/PCINT1) PE1
(XCK/AIN0/PCINT2) PE2
(AIN1/PCINT3) PE3
(USCK/SCL/PCINT4) PE4
(DI/SDA/PCINT5) PE5
(DO/PCINT6) PE6
(CLKO/PCINT7) PE7
VCC
GND
DNC
(PCINT24/SEG35) PJ0
(PCINT25/SEG34) PJ1
DNC
DNC
DNC
DNC
(SS/PCINT8) PB0
(SCK/PCINT9) PB1
(MOSI/PCINT10) PB2
(MISO/PCINT11) PB3
(OC0A/PCINT12) PB4
(OC1A/PCINT13) PB5
(OC1B/PCINT14) PB6
TQFP
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2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 1-2. Pinout ATmega329/649
Note: The large center pad underneath the QFN/MLF packages is made of metal and internally con-
nected to GND. It should be soldered or glued to the board to ensure good mechanical stability. If
the center pad is left unconnected, the package might loosen from the board.
PC0 (SEG12)
VCC
GND
PF0 (ADC0)
PF7 (ADC7/TDI)
PF1 (ADC1)
PF2 (ADC2)
PF3 (ADC3)
PF4 (ADC4/TCK)
PF5 (ADC5/TMS)
PF6 (ADC6/TDO)
AREF
GND
AVCC
17
61
60
18
59
20
58
19
21
57
22
56
23
55
24
54
25
53
26
52
27
51
29
28
50
49
32
31
30
(RXD/PCINT0) PE0
(TXD/PCINT1) PE1
LCDCAP
(XCK/AIN0/PCINT2) PE2
(AIN1/PCINT3) PE3
(USCK/SCL/PCINT4) PE4
(DI/SDA/PCINT5) PE5
(DO/PCINT6) PE6
(CLKO/PCINT7) PE7
(SCK/PCINT9) PB1
(MOSI/PCINT10) PB2
(MISO/PCINT11) PB3
(OC0A/PCINT12) PB4
(OC2A/PCINT15) PB7
(T1/SEG24) PG3
(OC1B/PCINT14) PB6
(T0/SEG23) PG4
(OC1A/PCINT13) PB5
PC1 (SEG11)
PG0 (SEG14)
(SEG15) PD7
PC2 (SEG10)
PC3 (SEG9)
PC4 (SEG8)
PC5 (SEG7)
PC6 (SEG6)
PC7 (SEG5)
PA7 (SEG3)
PG2 (SEG4)
PA6 (SEG2)
PA5 (SEG1)
PA4 (SEG0)
PA3 (COM3)
PA0 (COM0)
PA1 (COM1)
PA2 (COM2)
PG1 (SEG13)
(SEG16) PD6
(SEG17) PD5
(SEG18) PD4
(SEG19) PD3
(SEG20) PD2
(INT0/SEG21) PD1
(ICP1/SEG22) PD0
(TOSC1) XTAL1
(TOSC2) XTAL2
RESET/PG5
GND
VCC
INDEX CORNER
(SS/PCINT8) PB0
2
3
1
4
5
6
7
8
9
10
11
12
13
14
16
15
64
63
62
47
46
48
45
44
43
42
41
40
39
38
37
36
35
33
34
ATmega329/649
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2552K–AVR–04/11
ATmega329/3290/649/6490
2. Overview
The ATmega329/3290/649/6490 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC architec-
ture. By executing powerful instructions in a single clock cycle, the ATmega329/3290/649/6490 achieves throughputs
approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing speed.
2.1 Block Diagram
Figure 2-1. Block Diagram
PROGRAM
COUNTER
INTERNAL
OSCILLATOR
WATCHDOG
TIMER
STACK
POINTER
PROGRAM
FLASH
MCU CONTROL
REGISTER
SRAM
GENERAL
PURPOSE
REGISTERS
INSTRUCTION
REGISTER
TIMER/
COUNTERS
INSTRUCTION
DECODER
DATA DIR.
REG. PORTB
DATA DIR.
REG. PORTE
DATA DIR.
REG. PORTA
DATA DIR.
REG. PORTD
DATA REGISTER
PORTB
DATA REGISTER
PORTE
DATA REGISTER
PORTA
DATA REGISTER
PORTD
TIMING AND
CONTROL
OSCILLATOR
INTERRUPT
UNIT
EEPROM
SPI
USART
STATUS
REGISTER
Z
Y
X
ALU
PORTB DRIVERS
PORTE DRIVERS
PORTA DRIVERS
PORTF DRIVERS
PORTD DRIVERS
PORTC DRIVERS
PB0 - PB7PE0 - PE7
PA0 - PA7PF0 - PF7
VCCGND
XTAL1
XTAL2
CONTROL
LINES
+
-
ANALOG
COMPARATOR
PC0 - PC7
8-BIT DATA BUS
RESET
CALIB. OSC
DATA DIR.
REG. PORTC
DATA REGISTER
PORTC
ON-CHIP DEBUG
JTAG TAP
PROGRAMMING
LOGIC
BOUNDARY-
SCAN
DATA DIR.
REG. PORTF
DATA REGISTER
PORTF
ADC
PD0 - PD7
DATA DIR.
REG. PORTG
DATA REG.
PORTG
PORTG DRIVERS
PG0 - PG4
AGND
AREF
AVCC
UNIVERSAL
SERIAL INTERFACE
AVR CPU
LCD
CONTROLLER/
DRIVER
PORTH DRIVERS
PH0 - PH7
DATA DIR.
REG. PORTH
DATA REGISTER
PORTH
PORTJ DRIVERS
PJ0 - PJ6
DATA DIR.
REG. PORTJ
DATA REGISTER
PORTJ
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2552K–AVR–04/11
ATmega329/3290/649/6490
The Atmel® AVR® core combines a rich instruction set with 32 general purpose working regis-
ters. 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 ATmega329/3290/649/6490 provides the following features: 32/64K bytes of In-Sys-
tem Programmable Flash with Read-While-Write capabilities, 1/2K bytes EEPROM, 2/4K byte
SRAM, 54/69 general purpose I/O lines, 32 general purpose working registers, a JTAG interface
for Boundary-scan, On-chip Debugging support and programming, a complete On-chip LCD
controller with internal contrast control, three flexible Timer/Counters with compare modes, inter-
nal and external interrupts, a serial programmable USART, Universal Serial Interface with Start
Condition Detector, an 8-channel, 10-bit ADC, a programmable Watchdog Timer with internal
Oscillator, an SPI serial port, and five software selectable power saving modes. The Idle mode
stops the CPU while allowing the SRAM, Timer/Counters, SPI port, and interrupt system to con-
tinue functioning. The Power-down mode saves the register contents but freezes the Oscillator,
disabling all other chip functions until the next interrupt or hardware reset. In Power-save mode,
the asynchronous timer and the LCD controller continues to run, allowing the user to maintain a
timer base and operate the LCD display while the rest of the device is sleeping. The ADC Noise
Reduction mode stops the CPU and all I/O modules except asynchronous timer, LCD controller
and ADC, to minimize switching noise during ADC conversions. In Standby mode, the crys-
tal/resonator Oscillator is running while the rest of the device is sleeping. This allows very fast
start-up combined with low-power consumption.
The device is manufactured using Atmel’s high density non-volatile memory technology. The
On-chip In-System re-Programmable (ISP) Flash allows the program memory to be repro-
grammed In-System through an SPI serial interface, by a conventional non-volatile memory
programmer, or by an On-chip Boot program running on the AVR core. The Boot program can
use any interface to download the application program in the Application Flash memory. Soft-
ware in the Boot Flash section will continue to run while the Application Flash section is updated,
providing true Read-While-Write operation. By combining an 8-bit RISC CPU with In-System
Self-Programmable Flash on a monolithic chip, the Atmel ATmega329/3290/649/6490 is a pow-
erful microcontroller that provides a highly flexible and cost effective solution to many embedded
control applications.
The Atmel ATmega329/3290/649/6490 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.
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ATmega329/3290/649/6490
2.2 Comparison between ATmega329, ATmega3290, ATmega649 and ATmega6490
The ATmega329, ATmega3290, ATmega649, and ATmega6490 differs only in memory sizes,
pin count and pinout. Table 2-1 on page 6 summarizes the different configurations for the four
devices.
2.3 Pin Descriptions
The following section describes the I/O-pin special functions.
2.3.1 VCC
Digital supply voltage.
2.3.2 GND
Ground.
2.3.3 Port A (PA7..PA0)
Port A is an 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 also serves the functions of various special features of the ATmega329/3290/649/6490
as listed on page 67.
2.3.4 Port B (PB7..PB0)
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port B output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port B pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port B has better driving capabilities than the other ports.
Port B also serves the functions of various special features of the ATmega329/3290/649/6490
as listed on page 68.
Table 2-1. Configuration Summary
Device Flash EEPROM RAM
LCD
Segments
General Purpose
I/O Pins
ATmega329 32Kbytes 1Kbytes 2Kbytes 4 x 25 54
ATmega3290 32Kbytes 1K bytes 2Kbytes 4 x 40 69
ATmega649 64Kbytes 2Kbytes 4Kbytes 4 x 25 54
ATmega6490 64Kbytes 2Kbytes 4Kbytes 4 x 40 69
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ATmega329/3290/649/6490
2.3.5 Port C (PC7..PC0)
Port C is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port C output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port C pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port C pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port C also serves the functions of special features of the ATmega329/3290/649/6490 as listed
on page 71.
2.3.6 Port D (PD7..PD0)
Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port D output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port D pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port D pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port D also serves the functions of various special features of the ATmega329/3290/649/6490
as listed on page 73.
2.3.7 Port E (PE7..PE0)
Port E is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port E output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port E pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port E pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port E also serves the functions of various special features of the ATmega329/3290/649/6490
as listed on page 75.
2.3.8 Port F (PF7..PF0)
Port F serves as the analog inputs to the A/D Converter.
Port F also serves as an 8-bit bi-directional I/O port, if the A/D Converter is not used. Port pins
can provide internal pull-up resistors (selected for each bit). The Port F output buffers have sym-
metrical drive characteristics with both high sink and source capability. As inputs, Port F pins
that are externally pulled low will source current if the pull-up resistors are activated. The Port F
pins are tri-stated when a reset condition becomes active, even if the clock is not running. If the
JTAG interface is enabled, the pull-up resistors on pins PF7(TDI), PF5(TMS), and PF4(TCK) will
be activated even if a reset occurs.
Port F also serves the functions of the JTAG interface.
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ATmega329/3290/649/6490
2.3.9 Port G (PG5..PG0)
Port G is a 6-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port G output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port G pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port G pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port G also serves the functions of various special features of the ATmega329/3290/649/6490
as listed on page 75.
2.3.10 Port H (PH7..PH0)
Port H is a 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port H output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port H pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port H pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port H also serves the functions of various special features of the ATmega3290/6490 as listed
on page 75.
2.3.11 Port J (PJ6..PJ0)
Port J is a 7-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port J output buffers have symmetrical drive characteristics with both high sink and source capa-
bility. As inputs, Port J pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port J pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port J also serves the functions of various special features of the ATmega3290/6490 as listed on
page 75.
2.3.12 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 “System and Reset
Characteristics” on page 330. Shorter pulses are not guaranteed to generate a reset.
2.3.13 XTAL1
Input to the inverting Oscillator amplifier and input to the internal clock operating circuit.
2.3.14 XTAL2
Output from the inverting Oscillator amplifier.
2.3.15 AVCC
AVCC is the supply voltage pin for Port F and the A/D Converter. It should be externally con-
nected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC
through a low-pass filter.
2.3.16 AREF
This is the analog reference pin for the A/D Converter.
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2552K–AVR–04/11
ATmega329/3290/649/6490
2.3.17 LCDCAP
An external capacitor (typical > 470nF) must be connected to the LCDCAP pin as shown in Fig-
ure 23-2. This capacitor acts as a reservoir for LCD power (VLCD). A large capacitance reduces
ripple on VLCD but increases the time until VLCD reaches its target value.
3. Resources
A comprehensive set of development tools, application notes and datasheets are available for
download on http://www.atmel.com/avr.
Note: 1.
4. Data Retention
Reliability Qualification results show that the projected data retention failure rate is much less
than 1 PPM over 20 years at 85°C or 100 years at 25°C.
5. 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 documen-
tation 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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2552K–AVR–04/11
ATmega329/3290/649/6490
6. AVR CPU Core
6.1 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.
6.2 Architectural Overview
Figure 6-1. 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 instruc-
tion 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.
Flash
Program
Memory
Instruction
Register
Instruction
Decoder
Program
Counter
Control Lines
32 x 8
General
Purpose
Registrers
ALU
Status
and Control
I/O Lines
EEPROM
Data Bus 8-bit
Data
SRAM
Direct Addressing
Indirect Addressing
Interrupt
Unit
SPI
Unit
Watchdog
Timer
Analog
Comparator
I/O Module 2
I/O Module1
I/O Module n
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ATmega329/3290/649/6490
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 typ-
ical ALU operation, two operands are output from the Register File, the operation is executed,
and the result is stored back in the Register File – in one clock cycle.
Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data
Space addressing – enabling efficient address calculations. One of the these address pointers
can also be used as an address pointer for look up tables in Flash program memory. These
added function registers are the 16-bit X-, Y-, and Z-register, described later in this section.
The ALU supports arithmetic and logic operations between registers or between a constant and
a register. Single register operations can also be executed in the ALU. After an arithmetic opera-
tion, 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 for-
mat. Every program memory address contains a 16- or 32-bit instruction.
Program Flash memory space is divided in two sections, the Boot Program section and the
Application Program section. Both sections have dedicated Lock bits for write and read/write
protection. The SPM instruction that writes into the Application Flash memory section must
reside in the Boot Program section.
During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the
Stack. The Stack is effectively allocated in the general data SRAM, and consequently the Stack
size is only limited by the total SRAM size and the usage of the SRAM. All user programs must
initialize the SP in the Reset routine (before subroutines or interrupts are executed). The Stack
Pointer (SP) is read/write accessible in the I/O space. The data SRAM can easily be accessed
through the five different addressing modes supported in the AVR architecture.
The memory spaces in the AVR architecture are all linear and regular memory maps.
A flexible interrupt module has its control registers in the I/O space with an additional Global
Interrupt Enable bit in the Status Register. All interrupts have a separate Interrupt Vector in the
Interrupt Vector table. The interrupts have priority in accordance with their Interrupt Vector posi-
tion. The lower the Interrupt Vector address, the higher the priority.
The I/O memory space contains 64 addresses for CPU peripheral functions as Control Regis-
ters, SPI, and other I/O functions. The I/O Memory can be accessed directly, or as the Data
Space locations following those of the Register File, 0x20 - 0x5F. In addition, the
ATmega329/3290/649/6490 has Extended I/O space from 0x60 - 0xFF in SRAM where only the
ST/STS/STD and LD/LDS/LDD instructions can be used.
6.3 ALU – Arithmetic Logic Unit
The high-performance AVR ALU operates in direct connection with all the 32 general purpose
working registers. Within a single clock cycle, arithmetic operations between general purpose
registers or between a register and an immediate are executed. The ALU operations are divided
into three main categories – arithmetic, logical, and bit-functions. Some implementations of the
architecture also provide a powerful multiplier supporting both signed/unsigned multiplication
and fractional format. See the “Instruction Set” section for a detailed description.
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6.4 AVR Status Register
The Status Register contains information about the result of the most recently executed arithme-
tic 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.
6.4.1 SREG – AVR Status Register
The AVR Status Register – SREG – is defined as:
• Bit 7 – I: Global Interrupt Enable
The Global Interrupt Enable bit must be set for the interrupts to be enabled. The individual inter-
rupt enable control is then performed in separate control registers. If the Global Interrupt Enable
Register is cleared, none of the interrupts are enabled independent of the individual interrupt
enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is set by
the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared by
the application with the SEI and CLI instructions, as described in the instruction set reference.
• Bit 6 – T: Bit Copy Storage
The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or desti-
nation 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 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 Value 0 0 0 0 0 0 0 0
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• 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.
6.5 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 6-2 shows the structure of the 32 general purpose working registers in the CPU.
Figure 6-2. 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 6-2, 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 imple-
mented 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
R280x1C 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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6.5.1 The X-register, Y-register, and Z-register
The registers R26..R31 have some added functions to their general purpose usage. These reg-
isters 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 6-3.
Figure 6-3. 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).
6.6 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 loca-
tions 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 implementa-
tions of the AVR architecture is so small that only SPL is needed. In this case, the SPH Register
will not be present.
15 XH XL 0
X-register 707 0
R27 (0x1B) R26 (0x1A)
15 YH YL 0
Y-register 707 0
R29 (0x1D) R28 (0x1C)
15 ZH ZL 0
Z-register 70 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 Value 0 0 0 0 0 0 0 0
00000000
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6.7 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 6-4 shows the parallel instruction fetches and instruction executions enabled by the Har-
vard architecture and the fast-access Register File concept. This is the basic pipelining concept
to obtain up to 1 MIPS per MHz with the corresponding unique results for functions per cost,
functions per clocks, and functions per power-unit.
Figure 6-4. The Parallel Instruction Fetches and Instruction Executions
Figure 6-5 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 destina-
tion register.
Figure 6-5. Single Cycle ALU Operation
6.8 Reset and Interrupt Handling
The AVR provides several different interrupt sources. These interrupts and the separate Reset
Vector each have a separate program vector in the program memory space. All interrupts are
assigned individual enable bits which must be written logic one together with the Global Interrupt
Enable bit in the Status Register in order to enable the interrupt. Depending on the Program
Counter value, interrupts may be automatically disabled when Boot Lock bits BLB02 or BLB12
are programmed. This feature improves software security. See the section “Memory Program-
ming” on page 293 for details.
The lowest addresses in the program memory space are by default defined as the Reset and
Interrupt Vectors. The complete list of vectors is shown in “Interrupts” on page 49. The list also
determines the priority levels of the different interrupts. The lower the address the higher is the
clk
1st Instruction Fetch
1st Instruction Execute
2nd Instruction Fetch
2nd Instruction Execute
3rd Instruction Fetch
3rd Instruction Execute
4th Instruction Fetch
T1 T2 T3 T4
CPU
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back
T1 T2 T3 T4
clkCPU
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priority level. RESET has the highest priority, and next is INT0 – the External Interrupt Request
0. The Interrupt Vectors can be moved to the start of the Boot Flash section by setting the IVSEL
bit in the MCU Control Register (MCUCR). Refer to “Interrupts” on page 49 for more information.
The Reset Vector can also be moved to the start of the Boot Flash section by programming the
BOOTRST Fuse, see “Boot Loader Support – Read-While-Write Self-Programming” on page
278.
When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts are dis-
abled. 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 Vec-
tor in order to execute the interrupt handling routine, and hardware clears the corresponding
Interrupt Flag. Interrupt Flags can also be cleared by writing a logic one to the flag bit position(s)
to be cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is
cleared, the Interrupt Flag will be set and remembered until the interrupt is enabled, or the flag is
cleared by software. Similarly, if one or more interrupt conditions occur while the Global Interrupt
Enable bit is cleared, the corresponding Interrupt Flag(s) will be set and remembered until the
Global Interrupt Enable bit is set, and will then be executed by order of priority.
The second type of interrupts will trigger as long as the interrupt condition is present. These
interrupts do not necessarily have Interrupt Flags. If the interrupt condition disappears before the
interrupt is enabled, the interrupt will not be triggered.
When the AVR exits from an interrupt, it will always return to the main program and execute one
more instruction before any pending interrupt is served.
Note that the Status Register is not automatically stored when entering an interrupt routine, nor
restored when returning from an interrupt routine. This must be handled by software.
When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled.
No interrupt will be executed after the CLI instruction, even if it occurs simultaneously with the
CLI instruction. The following example shows how this can be used to avoid interrupts during the
timed EEPROM write sequence.
Assembly Code Example
in r16, SREG ; store SREG value
cli ; disable interrupts during timed sequence
sbi EECR, EEMWE ; start EEPROM write
sbi EECR, EEWE
out SREG, r16 ; restore SREG value (I-bit)
C Code Example
char cSREG;
cSREG = SREG; /* store SREG value */
/* disable interrupts during timed sequence */
__disable_interrupt();
EECR |= (1<<EEMWE); /* start EEPROM write */
EECR |= (1<<EEWE);
SREG = cSREG; /* restore SREG value (I-bit) */
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When using the SEI instruction to enable interrupts, the instruction following SEI will be exe-
cuted before any pending interrupts, as shown in this example.
6.8.1 Interrupt Response Time
The interrupt execution response for all the enabled AVR interrupts is four clock cycles mini-
mum. 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
sei ; set Global Interrupt Enable
sleep; enter sleep, waiting for interrupt
; note: will enter sleep before any pending
; interrupt(s)
C Code Example
__enable_interrupt(); /* set Global Interrupt Enable */
__sleep(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */
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7. AVR ATmega329/3290/649/6490 Memories
This section describes the different memories in the ATmega329/3290/649/6490. The Atmel®
AVR® architecture has two main memory spaces, the Data Memory and the Program Memory
space. In addition, the ATmega329/3290/649/6490 features an EEPROM Memory for data stor-
age. All three memory spaces are linear.
7.1 In-System Reprogrammable Flash Program Memory
The ATmega329/3290/649/6490 contains 32/64Kbytes 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 16/32K x 16. For software security, the Flash Program memory space is divided
into two sections, Boot Program section and Application Program section.
The Flash memory has an endurance of at least 10,000 write/erase cycles. The
ATmega329/3290/649/6490 Program Counter (PC) is 14/15 bits wide, thus addressing the
16/32K program memory locations. The operation of Boot Program section and associated Boot
Lock bits for software protection are described in detail in “Boot Loader Support – Read-While-
Write Self-Programming” on page 278. “Memory Programming” on page 293 contains a detailed
description on Flash data serial downloading using the SPI pins or the JTAG interface.
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 “Instruction Execution Tim-
ing” on page 15.
Figure 7-1. Program Memory Map
0x0000
0x3FFF/0x7FFF
Program Memory
Application Flash Section
Boot Flash Section
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7.2 SRAM Data Memory
Figure 7-2 shows how the ATmega329/3290/649/6490 SRAM Memory is organized.
The ATmega329/3290/649/6490 is a complex microcontroller with more peripheral units than
can be supported within the 64 locations reserved in the Opcode for the IN and OUT instruc-
tions. For the Extended I/O space from 0x60 - 0xFF in SRAM, only the ST/STS/STD and
LD/LDS/LDD instructions can be used.
The lower 2304/4352 data memory locations address both the Register File, the I/O memory,
Extended I/O memory, and the internal data SRAM. The first 32 locations address the Register
File, the next 64 location the standard I/O memory, then 160 locations of Extended I/O memory,
and the next 2048/4096 locations address the internal data SRAM.
The five different addressing modes for the data memory cover: Direct, Indirect with Displace-
ment, 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-incre-
ment, the address registers X, Y, and Z are decremented or incremented.
The 32 general purpose working registers, 64 I/O Registers, 160 Extended I/O Registers, and
the 2,048 bytes of internal data SRAM in the ATmega329/3290/649/6490 are all accessible
through all these addressing modes. The Register File is described in “General Purpose Regis-
ter File” on page 13.
Figure 7-2. Data Memory Map
7.2.1 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 7-3.
32 Registers
64 I/O Registers
Internal SRAM
(2048 x 8)/
(4096 x 8)
0x0000 - 0x001F
0x0020 - 0x005F
0x08FF/0x10FF
0x0060 - 0x00F
F
Data Memory
160 Ext I/O Reg.
0x0100
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Figure 7-3. On-chip Data SRAM Access Cycles
7.3 EEPROM Data Memory
The ATmega329/3290/649/6490 contains 1/2K 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 SPI, JTAG and Parallel data downloading to the EEPROM, see
page 308, page 313, and page 296 respectively.
7.3.1 EEPROM Read/Write Access
The EEPROM Access Registers are accessible in the I/O space.
The write access time for the EEPROM is given in Table 7-1. A self-timing function, however,
lets the user software detect when the next byte can be written. If the user code contains instruc-
tions 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 “Preventing EEPROM Corruption” on page 21. for details on how to avoid problems in these
situations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed.
Refer to the description of the EEPROM Control Register for details on this.
When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is
executed. When the EEPROM is written, the CPU is halted for two clock cycles before the next
instruction is executed.
7.3.2 EEPROM Write During Power-down Sleep Mode
When entering Power-down sleep mode while an EEPROM write operation is active, the
EEPROM write operation will continue, and will complete before the Write Access time has
passed. However, when the write operation is completed, the clock continues running, and as a
clk
WR
RD
Data
Data
Address Address valid
T1 T2 T3
Compute Address
Read Write
CPU
Memory Access Instruction Next Instruction
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consequence, the device does not enter Power-down entirely. It is therefore recommended to
verify that the EEPROM write operation is completed before entering Power-down.
7.3.3 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. Sec-
ondly, 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 com-
pleted provided that the power supply voltage is sufficient.
7.4 I/O Memory
The I/O space definition of the ATmega329/3290/649/6490 is shown in “Register Summary” on
page 365.
All ATmega329/3290/649/6490 I/Os and peripherals are placed in the I/O space. All I/O loca-
tions may be accessed by the LD/LDS/LDD and ST/STS/STD instructions, transferring data
between the 32 general purpose working registers and the I/O space. I/O Registers within the
address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In
these registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
Refer to the instruction set section for more details. When using the I/O specific commands IN
and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing I/O Registers as data
space using LD and ST instructions, 0x20 must be added to these addresses. The
ATmega329/3290/649/6490 is a complex microcontroller with more peripheral units than can be
supported within the 64 location reserved in Opcode for the IN and OUT instructions. For the
Extended I/O space from 0x60 - 0xFF in SRAM, only the ST/STS/STD and LD/LDS/LDD instruc-
tions can be used.
For compatibility with future devices, reserved bits should be written to zero if accessed.
Reserved I/O memory addresses should never be written.
Some of the Status Flags are cleared by writing a logical one to them. Note that, unlike most
other AVRs, the CBI and SBI instructions will only operate on the specified bit, and can therefore
be used on registers containing such Status Flags. The CBI and SBI instructions work with reg-
isters 0x00 to 0x1F only.
The I/O and peripherals control registers are explained in later sections.
7.4.1 General Purpose I/O Registers
The ATmega329/3290/649/6490 contains three General Purpose I/O Registers. These registers
can be used for storing any information, and they are particularly useful for storing global vari-
ables 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.
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7.5 Register Description
7.5.1 EEARH and EEARL – The EEPROM Address Register
• Bits 15:11 – Reserved Bits
These bits are reserved bits in the ATmega329/3290/649/6490 and will always read as zero.
• Bits 10:0 – EEAR10:0: EEPROM Address
The EEPROM Address Registers – EEARH and EEARL specify the EEPROM address in the
1/2K bytes EEPROM space. The EEPROM data bytes are addressed linearly between 0 and
1023/2047. The initial value of EEAR is undefined. A proper value must be written before the
EEPROM may be accessed.
Note: EEAR10 is only valid for ATmega649 and ATmega6490.
7.5.2 EEDR – The 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.
7.5.3 EECR – The EEPROM Control Register
• Bits 7:4 – Reserved Bits
These bits are reserved bits in the ATmega329/3290/649/6490 and will always read as zero.
• 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 inter-
rupt when EEWE is cleared.
• Bit 2 – EEMWE: EEPROM Master Write Enable
The EEMWE bit determines whether setting EEWE to one causes the EEPROM to be written.
When EEMWE is set, setting EEWE within four clock cycles will write data to the EEPROM at
Bit 151413121110 9 8
0x22 (0x42) – – – – – EEAR10 EEAR9 EEAR8 EEARH
0x21 (0x41) EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEARL
76543210
Read/WriteRRRRRR/WR/WR/W
R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 X X X
XXXXXXXX
Bit 76543210
0x20 (0x40) MSB LSB EEDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x1F (0x3F) ––––EERIEEEMWEEEWEEEREEECR
Read/Write R R R R R/W R/W R/W R/W
Initial Value000000X0
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the selected address If EEMWE is zero, setting EEWE will have no effect. When EEMWE has
been written to one by software, hardware clears the bit to zero after four clock cycles. See the
description of the EEWE bit for an EEPROM write procedure.
• Bit 1 – EEWE: EEPROM Write Enable
The EEPROM Write Enable Signal EEWE is the write strobe to the EEPROM. When address
and data are correctly set up, the EEWE bit must be written to one to write the value into the
EEPROM. The EEMWE bit must be written to one before a logical one is written to EEWE, oth-
erwise no EEPROM write takes place. The following procedure should be followed when writing
the EEPROM (the order of steps 3 and 4 is not essential):
1. Wait until EEWE becomes zero.
2. Wait until SPMEN in SPMCSR becomes zero.
3. Write new EEPROM address to EEAR (optional).
4. Write new EEPROM data to EEDR (optional).
5. Write a logical one to the EEMWE bit while writing a zero to EEWE in EECR.
6. Within four clock cycles after setting EEMWE, write a logical one to EEWE.
The EEPROM can not be programmed during a CPU write to the Flash memory. The software
must check that the Flash programming is completed before initiating a new EEPROM write.
Step 2 is only relevant if the software contains a Boot Loader allowing the CPU to program the
Flash. If the Flash is never being updated by the CPU, step 2 can be omitted. See “Boot Loader
Support – Read-While-Write Self-Programming” on page 278 for details about Boot
programming.
Caution: An interrupt between step 5 and step 6 will make the write cycle fail, since the
EEPROM Master Write Enable will time-out. If an interrupt routine accessing the EEPROM is
interrupting another EEPROM access, the EEAR or EEDR Register will be modified, causing the
interrupted EEPROM access to fail. It is recommended to have the Global Interrupt Flag cleared
during all the steps to avoid these problems.
When the write access time has elapsed, the EEWE bit is cleared by hardware. The user soft-
ware can poll this bit and wait for a zero before writing the next byte. When EEWE has been set,
the CPU is halted for two cycles before the next instruction is executed.
• Bit 0 – EERE: EEPROM Read Enable
The EEPROM Read Enable Signal EERE is the read strobe to the EEPROM. When the correct
address is set up in the EEAR Register, the EERE bit must be written to a logic one to trigger the
EEPROM read. The EEPROM read access takes one instruction, and the requested data is
available immediately. When the EEPROM is read, the CPU is halted for four cycles before the
next instruction is executed.
The user should poll the EEWE bit before starting the read operation. If a write operation is in
progress, it is neither possible to read the EEPROM, nor to change the EEAR Register.
The calibrated Oscillator is used to time the EEPROM accesses. Table 7-1 lists the typical pro-
gramming time for EEPROM access from the CPU.
Table 7-1. EEPROM Programming Time
Symbol
Number of Calibrated
RC Oscillator Cycles Typical Programming Time
EEPROM write (from CPU) 27,072 3.4ms
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The following code examples show one assembly and one C function for writing to the
EEPROM. The examples assume that interrupts are controlled (e.g. by disabling interrupts glob-
ally) so that no interrupts will occur during execution of these functions. The examples also
assume that no Flash Boot Loader is present in the software. If such code is present, the
EEPROM write function must also wait for any ongoing SPM command to finish.
The next code examples show assembly and C functions for reading the EEPROM. The exam-
ples assume that interrupts are controlled so that no interrupts will occur during execution of
these functions.
Assembly Code Example
EEPROM_write:
; Wait for completion of previous write
sbic EECR,EEWE
rjmp EEPROM_write
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Write data (r16) to Data Register
out EEDR,r16
; Write logical one to EEMWE
sbi EECR,EEMWE
; Start eeprom write by setting EEWE
sbi EECR,EEWE
ret
C Code Example
void EEPROM_write(unsigned int uiAddress, unsigned char ucData)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEWE))
;
/* Set up address and Data Registers */
EEAR = uiAddress;
EEDR = ucData;
/* Write logical one to EEMWE */
EECR |= (1<<EEMWE);
/* Start eeprom write by setting EEWE */
EECR |= (1<<EEWE);
}
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7.5.4 GPIOR2 – General Purpose I/O Register 2
7.5.5 GPIOR1 – General Purpose I/O Register 1
7.5.6 GPIOR0 – General Purpose I/O Register 0
Assembly Code Example
EEPROM_read:
; Wait for completion of previous write
sbic EECR,EEWE
rjmp EEPROM_read
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Start eeprom read by writing EERE
sbi EECR,EERE
; Read data from Data Register
in r16,EEDR
ret
C Code Example
unsigned char EEPROM_read(unsigned int uiAddress)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEWE))
;
/* Set up address register */
EEAR = uiAddress;
/* Start eeprom read by writing EERE */
EECR |= (1<<EERE);
/* Return data from Data Register */
return EEDR;
}
Bit 76543210
0x2B (0x4B) 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
0x2A (0x4A) 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
0x1E (0x3E) 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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8. System Clock and Clock Options
8.1 Clock Systems and their Distribution
Figure 8-1 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 “Power Manage-
ment and Sleep Modes” on page 35. The clock systems are detailed below.
Figure 8-1. Clock Distribution
8.1.1 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.
8.1.2 I/O Clock – clkI/O
The I/O clock is used by the majority of the I/O modules, like Timer/Counters, SPI, and USART.
The I/O clock is also used by the External Interrupt module, but note that some external inter-
rupts are detected by asynchronous logic, allowing such interrupts to be detected even if the I/O
clock is halted. Also note that start condition detection in the USI module is carried out asynchro-
nously when clkI/O is halted, enabling USI start condition detection in all sleep modes.
8.1.3 Flash Clock – clkFLASH
The Flash clock controls operation of the Flash interface. The Flash clock is usually active simul-
taneously with the CPU clock.
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8.1.4 Asynchronous Timer Clock – clkASY
The Asynchronous Timer clock allows the Asynchronous Timer/Counter and the LCD controller
to be clocked directly from an external clock or an external 32kHz clock crystal. The dedicated
clock domain allows using this Timer/Counter as a real-time counter even when the device is in
sleep mode. It also allows the LCD controller output to continue while the rest of the device is in
sleep mode.
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.
8.2 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.
Note: 1. For all fuses “1” means unprogrammed while “0” means programmed.
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 com-
mencing 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 8-
2. The frequency of the Watchdog Oscillator is voltage dependent as shown in “Typical Charac-
teristics” on page 335.
8.2.1 Default Clock Source
The device is shipped with CKSEL = “0010”, SUT = “10”, and CKDIV8 programmed. The default
clock source setting is the Internal RC Oscillator with longest start-up time and an initial system
clock prescaling of 8. This default setting ensures that all users can make their desired clock
source setting using an In-System or Parallel programmer.
Table 8-1. Device Clocking Options Select(1)
Device Clocking Option CKSEL3..0
External Crystal/Ceramic Resonator 1111 - 1000
External Low-frequency Crystal 0111 - 0110
Calibrated Internal RC Oscillator 0010
External Clock 0000
Reserved 0011, 0001, 0101, 0100
Table 8-2. Number of Watchdog Oscillator Cycles
Typ Time-out (VCC = 5.0V) Typ Time-out (VCC = 3.0V) Number of Cycles
4.1ms 4.3ms 4K (4,096)
65ms 69ms 64K (65,536)
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8.3 Crystal Oscillator
XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be con-
figured for use as an On-chip Oscillator, as shown in Figure 8-2. 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 8-3. For ceramic resonators, the capacitor values given by
the manufacturer should be used.
Figure 8-2. 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 8-3.
Notes: 1. This option should not be used with crystals, only with ceramic resonators.
The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in Table
8-4.
Table 8-3. 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
Table 8-4. 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
000 258 CK(1) 14CK + 4.1ms Ceramic resonator,
fast rising power
001 258 CK(1) 14CK + 65ms Ceramic resonator,
slowly rising power
010 1K CK
(2) 14CK Ceramic resonator,
BOD enabled
XTAL2
XTAL1
GND
C2
C1
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Note: 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 fre-
quency of the device, and if frequency stability at start-up is not important for the application.
8.4 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 the CKSEL Fuses to “0110” or “0111”. The crystal should
be connected as shown in Figure 8-2. When this Oscillator is selected, start-up times are deter-
mined by the SUT Fuses as shown in Table 8-5 and CKSEL1..0 as shown in Table 8-6.
Note: 1. This option should only be used if frequency stability at start-up is not important for the
application
8.5 Calibrated Internal RC Oscillator
The calibrated Internal RC Oscillator by default provides a 8.0MHz clock. The frequency is nom-
inal value at 3V and 25°C. The device is shipped with the CKDIV8 Fuse programmed. See
“System Clock Prescaler” on page 32 for more details.
011 1K CK
(2) 14CK + 4.1ms Ceramic resonator,
fast rising power
100 1K CK
(2) 14CK + 65ms Ceramic resonator,
slowly rising power
101 16K CK 14CK Crystal Oscillator,
BOD enabled
110 16K CK 14CK + 4.1ms Crystal Oscillator, fast
rising power
111 16K CK 14CK + 65ms Crystal Oscillator,
slowly rising power
Table 8-4. Start-up Times for the Crystal Oscillator Clock Selection (Continued)
CKSEL0 SUT1..0
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
(VCC = 5.0V)
Recommended
Usage
Table 8-5. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
SUT1..0 Additional Delay from Reset (VCC = 5.0V) Recommended Usage
00 14CK Fast rising power or BOD enabled
01 14CK + 4.1ms Slowly rising power
10 14CK + 65ms Stable frequency at start-up
11 Reserved
Table 8-6. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
CKSEL3..0
Start-up Time from
Power-down and Power-save Recommended Usage
0110(1) 1K CK
0111 32K CK Stable frequency at start-up
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This clock may be selected as the system clock by programming the CKSEL Fuses as shown in
Table 8-7 on page 30. 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 28-2 on page 329.
By changing the OSCCAL register from SW, see “OSCCAL – Oscillator Calibration Register” on
page 32, 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 28-2 on page 329.
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 cali-
bration value, see the section “Calibration Byte” on page 296.
Note: 1. The device is shipped with this option selected.
2. The frequency ranges are preliminary values.
3. If 8MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8
Fuse can be programmed in order to divide the internal frequency by 8.
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 8-8 on page 30.
Note: 1. The device is shipped with this option selected.
Table 8-7. Internal Calibrated RC Oscillator Operating Modes(1)(3)
Frequency Range(2) (MHz) CKSEL3..0
7.3 - 8.1 0010
Table 8-8. Start-up times for the internal calibrated RC Oscillator clock selection
Power Conditions
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset (VCC = 5.0V) SUT1..0
BOD enabled 6 CK 14CK 00
Fast rising power 6 CK 14CK + 4.1ms 01
Slowly rising power 6 CK 14CK + 65ms(1) 10
Reserved 11
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8.6 External Clock
To drive the device from an external clock source, XTAL1 should be driven as shown in Figure
8-3. To run the device on an external clock, the CKSEL Fuses must be programmed to “0000”.
Figure 8-3. External Clock Drive Configuration
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 8-10.
When applying an external clock, it is required to avoid sudden changes in the applied clock fre-
quency 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. Refer to “System Clock Prescaler” on page
32 for details.
8.7 Clock Output Buffer
When the CKOUT Fuse is programmed, the system Clock will be output on CLKO. This mode is
suitable when the chip clock is used to drive other circuits on the system. The clock will be out-
put also during reset and the normal operation of I/O pin will be overridden when the fuse is
programmed. Any clock source, including internal RC Oscillator, can be selected when CLKO
Table 8-9. Crystal Oscillator Clock Frequency
CKSEL3..0 Frequency Range
0000 0 - 16MHz
Table 8-10. Start-up Times for the External Clock Selection
SUT1..0
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset (VCC = 5.0V) Recommended Usage
00 6 CK 14CK BOD enabled
01 6 CK 14CK + 4.1ms Fast rising power
10 6 CK 14CK + 65ms Slowly rising power
11 Reserved
NC
EXTERNAL
CLOCK
SIGNAL
XTAL2
XTAL1
GND
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serves as clock output. If the System Clock Prescaler is used, it is the divided system clock that
is output when the CKOUT Fuse is programmed.
8.8 Timer/Counter Oscillator
ATmega329/3290/649/6490 share the Timer/Counter Oscillator Pins (TOSC1 and TOSC2) with
XTAL1 and XTAL2. This means that the Timer/Counter Oscillator can only be used when the
calibrated internal RC Oscillator is selected as system clock source. The Oscillator is optimized
for use with a 32.768kHz watch crystal. See Figure 8-2 on page 28 for crystal connection.
Applying an external clock source to TOSC1 can be done if EXTCLK in the ASSR Register is
written to logic one. See “Asynchronous Operation of Timer/Counter2” on page 151 for further
description on selecting external clock as input instead of a 32kHz crystal.
8.9 System Clock Prescaler
The ATmega329/3290/649/6490 system clock can be divided by setting the Clock Prescale
Register – CLKPR. This feature can be used to decrease power consumption when the require-
ment 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 clk-
FLASH are divided by a factor as shown in Table 8-11 on page 34.
8.9.1 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.
8.10 Register Description
8.10.1 OSCCAL – Oscillator Calibration Register
• Bits 7:0 – CAL7:0: Oscillator Calibration Value
The Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator to
remove process variations from the oscillator frequency. A pre-programmed calibration value is
automatically written to this register during chip reset, giving the Factory calibrated frequency as
specified in Table 28-2 on page 329. The application software can write this register to change
the oscillator frequency. The oscillator can be calibrated to frequencies as specified in Table 28-
2 on page 329. Calibration outside that range is not guaranteed.
Bit 76543210
(0x66) 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
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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 fre-
quency 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.
8.10.2 CLKPR – Clock Prescale Register
• Bit 7 – CLKPCE: Clock Prescaler Change Enable
The CLKPCE bit must be written to logic one to enable change of the CLKPS bits. The CLKPCE
bit is only updated when the other bits in CLKPR are simultaneously written to zero. CLKPCE is
cleared by hardware four cycles after it is written or when CLKPS bits are written. Rewriting the
CLKPCE bit within this time-out period does neither extend the time-out period, nor clear the
CLKPCE bit.
• 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 synchro-
nous peripherals is reduced when a division factor is used. The division factors are given in
Table 8-11.
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 8 at start up. This feature should be used if the selected clock
source has a higher frequency than the maximum frequency of the device at the present operat-
ing 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.
Bit 76543210
(0x61) 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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Table 8-11. Clock Prescaler Select
CLKPS3 CLKPS2 CLKPS1 CLKPS0 Clock Division Factor
0000 1
0001 2
0010 4
0011 8
0100 16
0101 32
0110 64
0111 128
1000 256
1001 Reserved
1010 Reserved
1011 Reserved
1100 Reserved
1101 Reserved
1110 Reserved
1111 Reserved
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9. 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 consump-
tion to the application’s requirements.
To enter any of the five sleep modes, the SE bit in SMCR must be written to logic one and a
SLEEP instruction must be executed, see “SMCR – Sleep Mode Control Register” on page 39.
The SM2, SM1, and SM0 bits in the SMCR Register select which sleep mode (Idle, ADC Noise
Reduction, Power-down, Power-save, or Standby) will be activated by the SLEEP instruction.
See Table 9-1 on page 35 for a summary. If an enabled interrupt occurs while the MCU is in a
sleep mode, the MCU wakes up. The MCU is then halted for four cycles in addition to the start-
up time, executes the interrupt routine, and resumes execution from the instruction following
SLEEP. The contents of the Register File and SRAM are unaltered when the device wakes up
from sleep. If a reset occurs during sleep mode, the MCU wakes up and executes from the
Reset Vector.
Figure 8-1 on page 26 presents the different clock systems in the ATmega329/3290/649/6490,
and their distribution. The figure is helpful in selecting an appropriate sleep mode.
Notes: 1. Only recommended with external crystal or resonator selected as clock source.
2. If either LCD controller or Timer/Counter2 is running in asynchronous mode.
3. For INT0, only level interrupt
Table 9-1. 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
clkASY
Main Clock
Source
Enabled
Timer Osc
Enabled
INT0 and Pin
Change
USI Start
Condition
LCD
Controller
Timer2
SPM/EEPROM
Ready
ADC
Other I/O
Idle X X X X X(2) XX XXXXX
ADC
Noise
Reduction X X X X(2) X(3) XX
(2) X(2) XX
Power-
down X(3) X
Power-
save X X(2) X(3) XXX
Standby(1) XX
(3) X
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9.1 Idle Mode
When the SM2..0 bits are written to 000, the SLEEP instruction makes the MCU enter Idle
mode, stopping the CPU but allowing LCD controller, the SPI, USART, Analog Comparator,
ADC, USI, Timer/Counters, Watchdog, and the interrupt system to continue operating. This
sleep mode basically halts clkCPU and clkFLASH, while allowing the other clocks to run.
Idle mode enables the MCU to wake up from external triggered interrupts as well as internal
ones like the Timer Overflow and USART Transmit Complete interrupts. If wake-up from the
Analog Comparator interrupt is not required, the Analog Comparator can be powered down by
setting the ACD bit in the Analog Comparator Control and Status Register – ACSR. This will
reduce power consumption in Idle mode. If the ADC is enabled, a conversion starts automati-
cally when this mode is entered.
9.2 ADC Noise Reduction Mode
When the SM2..0 bits are written to 001, the SLEEP instruction makes the MCU enter ADC
Noise Reduction mode, stopping the CPU but allowing the ADC, the external interrupts, the USI
start condition detection, Timer/Counter2, LCD Controller, and the Watchdog to continue operat-
ing (if enabled). This sleep mode basically halts clkI/O, clkCPU, and clkFLASH, while allowing the
other clocks to run.
This improves the noise environment for the ADC, enabling higher resolution measurements. If
the ADC is enabled, a conversion starts automatically when this mode is entered. Apart form the
ADC Conversion Complete interrupt, only an External Reset, a Watchdog Reset, a Brown-out
Reset, an LCD controller interrupt, USI start condition interrupt, a Timer/Counter2 interrupt, 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.
9.3 Power-down Mode
When the SM2..0 bits are written to 010, the SLEEP instruction makes the MCU enter Power-
down mode. In this mode, the external Oscillator is stopped, while the external interrupts, the
USI start condition detection, and the Watchdog continue operating (if enabled). Only an Exter-
nal Reset, a Watchdog Reset, a Brown-out Reset, USI start condition interrupt, an external level
interrupt on INT0, or a pin change interrupt can wake up the MCU. This sleep mode basically
halts all generated clocks, allowing operation of asynchronous modules only.
Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed
level must be held for some time to wake up the MCU. Refer to “External Interrupts” on page 54
for details.
When waking up from Power-down mode, there is a delay from the wake-up condition occurs
until the wake-up becomes effective. This allows the clock to restart and become stable after
having been stopped. The wake-up period is defined by the same CKSEL Fuses that define the
Reset Time-out period, as described in “Clock Sources” on page 27.
9.4 Power-save Mode
When the SM2..0 bits are written to 011, the SLEEP instruction makes the MCU enter Power-
save mode. This mode is identical to Power-down, with one exception:
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If Timer/Counter2 and/or the LCD controller are enabled, they will keep running during sleep.
The device can wake up from either Timer Overflow or Output Compare event from
Timer/Counter2 if the corresponding Timer/Counter2 interrupt enable bits are set in TIMSK2,
and the Global Interrupt Enable bit in SREG is set. It can also wake up from an LCD controller
interrupt.
If neither Timer/Counter2 nor the LCD controller is running, Power-down mode is recommended
instead of Power-save mode.
The LCD controller and Timer/Counter2 can be clocked both synchronously and asynchronously
in Power-save mode. The clock source for the two modules can be selected independent of
each other. If neither the LCD controller nor the Timer/Counter2 is using the asynchronous
clock, the Timer/Counter Oscillator is stopped during sleep. If neither the LCD controller nor the
Timer/Counter2 is using the synchronous clock, the clock source is stopped during sleep. Note
that even if the synchronous clock is running in Power-save, this clock is only available for the
LCD controller and Timer/Counter2.
9.5 Standby Mode
When the SM2..0 bits are 110 and an external crystal/resonator clock option is selected, the
SLEEP instruction makes the MCU enter Standby mode. This mode is identical to Power-down
with the exception that the Oscillator is kept running. From Standby mode, the device wakes up
in six clock cycles.
9.6 Power Reduction Register
The Power Reduction Register (PRR), see “PRR – Power Reduction Register” on page 40, pro-
vides a method to stop the clock to individual peripherals to reduce power consumption. The
current state of the peripheral is frozen and the I/O registers inaccessible. Resources used by
the peripheral when stopping the clock will remain occupied so the peripheral should be disabled
before stopping the clock. Waking up a peripheral, which is done by clearing the bit in PRR, puts
the peripheral in the same state as before shutdown.
Peripheral shutdown can be used in Idle mode and Active mode to reduce the overall power
consumption. In all other sleep modes, the clock is already stopped.
9.7 Minimizing Power Consumption
There are several possibilities to consider when trying to minimize the power consumption in an
AVR controlled system. In general, sleep modes should be used as much as possible, and the
sleep mode should be selected so that as few as possible of the device’s functions are operat-
ing. 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.
9.7.1 Analog to Digital Converter
If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be dis-
abled before entering any sleep mode. When the ADC is turned off and on again, the next
conversion will be an extended conversion. Refer to “Analog to Digital Converter” on page 211
for details on ADC operation.
9.7.2 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 other sleep modes,
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the Analog Comparator is automatically disabled. However, if the Analog Comparator is set up
to use the Internal Voltage Reference as input, the Analog Comparator should be disabled in all
sleep modes. Otherwise, the Internal Voltage Reference will be enabled, independent of sleep
mode. Refer to “Analog Comparator” on page 207 for details on how to configure the Analog
Comparator.
9.7.3 Brown-out Detector
If the Brown-out Detector is not needed by the application, this module should be turned off. If
the Brown-out Detector is enabled by the BODLEVEL Fuses, it will be enabled in all sleep
modes, and hence, always consume power. In the deeper sleep modes, this will contribute sig-
nificantly to the total current consumption. Refer to “Brown-out Detection” on page 43 for details
on how to configure the Brown-out Detector.
9.7.4 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. Refer to “Internal Volt-
age Reference” on page 44 for details on the start-up time.
9.7.5 Watchdog Timer
If the Watchdog Timer is not needed in the application, the module should be turned off. If the
Watchdog Timer is enabled, it will be enabled in all sleep modes, and hence, always consume
power. In the deeper sleep modes, this will contribute significantly to the total current consump-
tion. Refer to “Watchdog Timer” on page 45 for details on how to configure the Watchdog Timer.
9.7.6 Port Pins
When entering a sleep mode, all port pins should be configured to use minimum power. The
most important is then to ensure that no pins drive resistive loads. In sleep modes where both
the I/O clock (clkI/O) and the ADC clock (clkADC) are stopped, the input buffers of the device will
be disabled. This ensures that no power is consumed by the input logic when not needed. In
some cases, the input logic is needed for detecting wake-up conditions, and it will then be
enabled. Refer to the section “Digital Input Enable and Sleep Modes” on page 64 for details on
which pins are enabled. If the input buffer is enabled and the input signal is left floating or have
an analog signal level close to VCC/2, the input buffer will use excessive power.
For analog input pins, the digital input buffer should be disabled at all times. An analog signal
level close to VCC/2 on an input pin can cause significant current even in active mode. Digital
input buffers can be disabled by writing to the Digital Input Disable Registers (DIDR1 and
DIDR0). Refer to “DIDR1 – Digital Input Disable Register 1” on page 210 and “DIDR0 – Digital
Input Disable Register 0” on page 227 for details.
9.7.7 JTAG Interface and On-chip Debug System
If the On-chip debug system is enabled by the OCDEN Fuse and the chip enter Power down or
Power save sleep mode, the main clock source remains enabled. In these sleep modes, this will
contribute significantly to the total current consumption. There are three alternative ways to
avoid this:
• Disable OCDEN Fuse.
• Disable JTAGEN Fuse.
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• Write one to the JTD bit in MCUCSR.
The TDO pin is left floating when the JTAG interface is enabled while the JTAG TAP controller is
not shifting data. If the hardware connected to the TDO pin does not pull up the logic level,
power consumption will increase. Note that the TDI pin for the next device in the scan chain con-
tains a pull-up that avoids this problem. Writing the JTD bit in the MCUCSR register to one or
leaving the JTAG fuse unprogrammed disables the JTAG interface.
9.8 Register Description
9.8.1 SMCR – Sleep Mode Control Register
The Sleep Mode Control Register contains control bits for power management.
• Bits 3, 2, 1 – SM2:0: Sleep Mode Select Bits 2, 1, and 0
These bits select between the five available sleep modes as shown in Table 9-2.
Note: 1. Standby mode is only recommended for use with external crystals or resonators.
• Bit 1 – 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.
Bit 76543210
0x33 (0x53) –––– SM2 SM1 SM0 SE SMCR
Read/Write R R R R R/W R/W R/W R/W
Initial Value00000000
Table 9-2. Sleep Mode Select
SM2 SM1 SM0 Sleep Mode
000Idle
001ADC Noise Reduction
010Power-down
011Power-save
100Reserved
101Reserved
110Standby
(1)
111Reserved
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9.8.2 PRR – Power Reduction Register
• Bits 7, 6, 5 - Reserved bits
These bits are reserved bits in ATmega329/3290/649/6490 and will always read as zero.
• Bit 4 - PRLCD: Power Reduction LCD
Writing logic one to this bit shuts down the LCD controller. The LCD controller must be disabled
and the display discharged before shut down. See "Disabling the LCD" on page 217 for details
on how to disable the LCD controller.
• Bit 3 - PRTIM1: Power Reduction Timer/Counter1
Writing logic one to this bit shuts down the Timer/Counter1 module. When Timer/Counter1 is
enabled, operation will continue like before the shutdown.
• Bit 2 - PRSPI: Power Reduction Serial Peripheral Interface
Writing logic one to this bit shuts down the Serial Peripheral Interface by stopping the clock to
the module. When waking up the SPI again, the SPI should be re-initialized to ensure proper
operation.
• Bit 1 - PRUSART: Power Reduction USART
Writing logic one to this bit shuts down the USART by stopping the clock to the module. When
waking up the USART again, the USART should be re-initialized to ensure proper operation.
• Bit 0 - PRADC: Power Reduction ADC
Writing 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.
Note: The Analog Comparator is disabled using the ACD-bit in the “ACSR – Analog Comparator Control
and Status Register” on page 209.
Bit 76543210
(0x64) – – – PRLCD PRTIM1 PRSPI PRUSART0 PRADC PRR
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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10. System Control and Reset
10.1 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 JMP – Absolute
Jump – instruction to the reset handling routine. If the program never enables an interrupt
source, the Interrupt Vectors are not used, and regular program code can be placed at these
locations. This is also the case if the Reset Vector is in the Application section while the Interrupt
Vectors are in the Boot section or vice versa. The circuit diagram in Figure 10-1 shows the reset
logic. “System and Reset Characteristics” on page 330 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 dif-
ferent selections for the delay period are presented in “Clock Sources” on page 27.
10.2 Reset Sources
The ATmega329/3290/649/6490 has five sources of reset:
• Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset
threshold (VPOT).
• External Reset. The MCU is reset when a low level is present on the RESET pin for longer
than the minimum pulse length.
• Watchdog 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.
• JTAG AVR Reset. The MCU is reset as long as there is a logic one in the Reset Register,
one of the scan chains of the JTAG system. Refer to the section “IEEE 1149.1 (JTAG)
Boundary-scan” on page 251 for details.
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Figure 10-1. Reset Logic
10.3 Power-on Reset
A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level
is defined in “System and Reset Characteristics” on page 330. 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 10-2. MCU Start-up, RESET Tied to VCC
MCU Status
Register (MCUSR)
Brown-out
Reset Circuit
BODLEVEL [1..0]
Delay Counters
CKSEL[3:0]
CK
TIMEOUT
WDRF
BORF
EXTRF
PORF
DATA BUS
Clock
Generator
SPIKE
FILTER
Pull-up Resistor
JTRF
JTAG Reset
Register
Watchdog
Oscillator
SUT[1:0]
Power-on Reset
Circuit
V
RESET
TIME-OUT
INTERNAL
RESET
t
TOUT
V
POT
V
RST
CC
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Figure 10-3. MCU Start-up, RESET Extended Externally
10.4 External Reset
An External Reset is generated by a low level on the RESET pin. Reset pulses longer than the
minimum pulse width (see “System and Reset Characteristics” on page 330) 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 10-4. External Reset During Operation
10.5 Brown-out Detection
ATmega329/3290/649/6490 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
10-5), the Brown-out Reset is immediately activated. When VCC increases above the trigger
level (VBOT+ in Figure 10-5), 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 lon-
ger than tBOD given in “System and Reset Characteristics” on page 330.
RESET
TIME-OUT
INTERNAL
RESET
t
TOUT
V
POT
V
RST
VCC
CC
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Figure 10-5. Brown-out Reset During Operation
10.6 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. Refer to
page 45 for details on operation of the Watchdog Timer.
Figure 10-6. Watchdog Reset During Operation
10.7 Internal Voltage Reference
ATmega329/3290/649/6490 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.
10.7.1 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 “System and Reset Characteristics” on page 330. 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 [1..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
VCC
RESET
TIME-OUT
INTERNAL
RESET
VBOT-
VBOT+
tTOUT
CK
CC
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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.
10.8 Watchdog Timer
The Watchdog Timer is clocked from a separate On-chip Oscillator which runs at 1 MHz. This is
the typical value at VCC = 5V. See characterization data for typical values at other VCC levels. By
controlling the Watchdog Timer prescaler, the Watchdog Reset interval can be adjusted as
shown in Table 10-2 on page 46. The WDR – Watchdog Reset – instruction resets the Watch-
dog Timer. The Watchdog Timer is also reset when it is disabled and when a Chip Reset occurs.
Eight different clock cycle periods can be selected to determine the reset period. If the reset
period expires without another Watchdog Reset, the ATmega329/3290/649/6490 resets and
executes from the Reset Vector. For timing details on the Watchdog Reset, refer to Table 10-2
on page 46.
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 10-1. Refer to
“Timed Sequences for Changing the Configuration of the Watchdog Timer” on page 47 for
details.
Figure 10-7. Watchdog Timer
Table 10-1. 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 1 Disabled Timed sequence Timed sequence
Programmed 2 Enabled Always enabled Timed sequence
WATCHDOG
OSCILLATOR
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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 “About Code Examples” on page 9.
Table 10-2. Watchdog Timer Prescale Select
WDP2 WDP1 WDP0
Number of WDT
Oscillator Cycles
Typical Time-out
at VCC = 3.0V
Typical Time-out
at VCC = 5.0V
0 0 0 16K cycles 17.1ms 16.3ms
0 0 1 32K cycles 34.3ms 32.5ms
0 1 0 64K cycles 68.5ms 65ms
011 128K cycles 0.14s 0.13s
1 0 0 256K cycles 0.27s 0.26s
1 0 1 512K cycles 0.55s 0.52s
1 1 0 1,024K cycles 1.1s 1.0s
111 2,048K cycles 2.2s 2.1s
Assembly Code Example(1)
WDT_off:
; Reset WDT
wdr
; Write logical one to WDCE and WDE
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)
{
/* Reset WDT */
__watchdog_reset();
/* Write logical one to WDCE and WDE */
WDTCR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCR = 0x00;
}
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10.9 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.
10.9.1 Safety Level 1
In this mode, the Watchdog Timer is initially disabled, but can be enabled by writing the WDE bit
to 1 without any restriction. A timed sequence is needed when changing the Watchdog Time-out
period or disabling an enabled Watchdog Timer. To disable an enabled Watchdog Timer, and/or
changing the Watchdog Time-out, 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.
10.9.2 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.
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.
10.10 Register Description
10.10.1 MCUSR – MCU Status Register
The MCU Status Register provides information on which reset source caused an MCU reset.
• Bit 4 – JTRF: JTAG Reset Flag
This bit is set if a reset is being caused by a logic one in the JTAG Reset Register selected by
the JTAG instruction AVR_RESET. This bit is reset by a Power-on Reset, or by writing a logic
zero to the flag.
• 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 76543210
0x35 (0x55) ––– JTRF WDRF BORF EXTRF PORF MCUSR
Read/Write R R R R/W R/W R/W R/W R/W
Initial Value 0 0 0 See Bit Description
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• 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.
10.10.2 WDTCR – Watchdog Timer Control Register
• Bits 7:5 – Reserved Bits
These bits are reserved bits in the ATmega329/3290/649/6490 and will always read as zero.
• 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. Refer to the
description of the WDE bit for a Watchdog disable procedure. This bit must also be set when
changing the prescaler bits. See “Timed Sequences for Changing the Configuration of the
Watchdog Timer” on page 47.
• 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 “Timed Sequences for Changing the Configuration of the Watchdog
Timer” on page 47.
• Bits 2:0 – WDP2, WDP1, WDP0: Watchdog Timer Prescaler 2, 1, and 0
The WDP2, WDP1, and WDP0 bits determine the Watchdog Timer prescaling when the Watch-
dog Timer is enabled. The different prescaling values and their corresponding Time-out Periods
are shown in Table 10-2 on page 46.
Bit 76543210
(0x60) – – – WDCE WDE WDP2 WDP1 WDP0 WDTCR
Read/Write R R R R/W R/W R/W R/W R/W
Initial Value00000000
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11. Interrupts
This section describes the specifics of the interrupt handling as performed in
ATmega329/3290/649/6490. For a general explanation of the AVR interrupt handling, refer to
“Reset and Interrupt Handling” on page 15.
11.1 Interrupt Vectors in ATmega329/3290/649/6490
Note: 1. When the BOOTRST Fuse is programmed, the device will jump to the Boot Loader address at
reset, see “Boot Loader Support – Read-While-Write Self-Programming” on page 278.
2. When the IVSEL bit in MCUCR is set, Interrupt Vectors will be moved to the start of the Boot
Flash Section. The address of each Interrupt Vector will then be the address in this table
added to the start address of the Boot Flash Section.
3. PCINT2 and PCINT3 are only present in ATmega3290 and ATmega6490.
Table 11-1. Reset and Interrupt Vectors
Vector
No.
Program
Address(2) Source Interrupt Definition
1 0x0000(1) RESET External Pin, Power-on Reset, Brown-out Reset,
Watchdog Reset, and JTAG AVR Reset
2 0x0002 INT0 External Interrupt Request 0
3 0x0004 PCINT0 Pin Change Interrupt Request 0
4 0x0006 PCINT1 Pin Change Interrupt Request 1
5 0x0008TIMER2 COMP Timer/Counter2 Compare Match
6 0x000A TIMER2 OVF Timer/Counter2 Overflow
7 0x000C TIMER1 CAPT Timer/Counter1 Capture Event
80x000E TIMER1 COMPA Timer/Counter1 Compare Match A
9 0x0010 TIMER1 COMPB Timer/Counter1 Compare Match B
10 0x0012 TIMER1 OVF Timer/Counter1 Overflow
11 0x0014 TIMER0 COMP Timer/Counter0 Compare Match
12 0x0016 TIMER0 OVF Timer/Counter0 Overflow
13 0x0018SPI, STC SPI Serial Transfer Complete
14 0x001A USART, RX USART0, Rx Complete
15 0x001C USART, UDRE USART0 Data Register Empty
16 0x001E USART, TX USART0, Tx Complete
17 0x0020 USI START USI Start Condition
180x0022 USI OVERFLOW USI Overflow
19 0x0024 ANALOG COMP Analog Comparator
20 0x0026 ADC ADC Conversion Complete
21 0x0028EE READY EEPROM Ready
22 0x002A SPM READY Store Program Memory Ready
23 0x002C LCD LCD Start of Frame
24(3) 0x002E PCINT2 Pin Change Interrupt Request 2
25(3) 0x0030 PCINT3 Pin Change Interrupt Request 3
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Table 11-2 shows reset and Interrupt Vectors placement for the various combinations of
BOOTRST and IVSEL settings. If the program never enables an interrupt source, the Interrupt
Vectors are not used, and regular program code can be placed at these locations. This is also
the case if the Reset Vector is in the Application section while the Interrupt Vectors are in the
Boot section or vice versa.
Note: 1. The Boot Reset Address is shown in Table 26-6 on page 290. For the BOOTRST Fuse “1”
means unprogrammed while “0” means programmed.
The most typical and general program setup for the Reset and Interrupt Vector Addresses in
ATmega329/3290/649/6490 is:
Table 11-2. Reset and Interrupt Vectors Placement(1)
BOOTRST IVSEL Reset Address Interrupt Vectors Start Address
1 0 0x0000 0x0002
1 1 0x0000 Boot Reset Address + 0x0002
0 0 Boot Reset Address 0x0002
0 1 Boot Reset Address Boot Reset Address + 0x0002
Addre
ss
Label
s
Code Comments
0x000
0
jmp RESET ; Reset Handler
0x000
2
jmp EXT_INT0 ; IRQ0 Handler
0x000
4
jmp PCINT0 ; PCINT0 Handler
0x000
6
jmp PCINT1 ; PCINT1 Handler
0x000
8
jmp TIM2_COMP ; Timer2 Compare Handler
0x000
A
jmp TIM2_OVF ; Timer2 Overflow Handler
0x000
C
jmp TIM1_CAPT ; Timer1 Capture Handler
0x000
E
jmp TIM1_COMPA ; Timer1 CompareA Handler
0x001
0
jmp TIM1_COMPB ; Timer1 CompareB Handler
0x001
2
jmp TIM1_OVF ; Timer1 Overflow Handler
0x001
4
jmp TIM0_COMP ; Timer0 Compare Handler
0x001
6
jmp TIM0_OVF ; Timer0 Overflow Handler
0X001
8
jmp SPI_STC ; SPI Transfer Complete Handler
0x001
A
jmp USART_RXC ; USART0 RX Complete Handler
0x001
C
jmp USART_UDRE ; USART0,UDR0 Empty Handler
0x001
E
jmp USART_TXC ; USART0 TX Complete Handler
0x002
0
jmp USI_STRT ; USI Start Condition Handler
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When the BOOTRST Fuse is unprogrammed, the Boot section size set to 4K bytes and the
IVSEL bit in the MCUCR Register is set before any interrupts are enabled, the most typical and
general program setup for the Reset and Interrupt Vector Addresses is:
Address Labels Code Comments
0x0000 RESET: ldi r16,high(RAMEND); Main program start
0x0001 out SPH,r16 ; Set Stack Pointer to top of RAM
0x0002 ldi r16,low(RAMEND)
0x0003 out SPL,r16
0x0004 sei ; Enable interrupts
0x0005 <instr> xxx
;
.org 0x3802/0x7802
0x3804/0x7804 jmp EXT_INT0 ; IRQ0 Handler
0x3806/0x7806 jmp PCINT0 ; PCINT0 Handler
... ... ... ;
0x1C2C jmp SPM_RDY ; Store Program Memory Ready Handler
When the BOOTRST Fuse is programmed and the Boot section size set to 4K bytes, the most
typical and general program setup for the Reset and Interrupt Vector Addresses is:
Address Labels Code Comments
.org 0x0002
0x0002 jmp EXT_INT0 ; IRQ0 Handler
0x002
2
jmp USI_OVF ; USI Overflow Handler
0x002
4
jmp ANA_COMP ; Analog Comparator Handler
0x002
6
jmp ADC ; ADC Conversion Complete
Handler
0x002
8
jmp EE_RDY ; EEPROM Ready Handler
0x002
A
jmp SPM_RDY ; SPM Ready Handler
0x002
C
jmp LCD_SOF ; LCD Start of Frame Handler
0x002
E
jmp PCINT2 ; PCINT2 Handler
0x003
0
jmp PCINT3 ; PCINT3 Handler
;
0x003
2
RESET
:
ldi r16,
high(RAMEND)
; Main program start
0x003
3
out SPH,r16 ; Set Stack Pointer to top of
RAM
0x003
4
ldi r16, low(RAMEND)
0x003
5
out SPL,r16
0x003
6
sei ; Enable interrupts
0x003
7
<ins
tr>
xxx
... ... ...
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0x0004 jmp PCINT0 ; PCINT0 Handler
... ... ... ;
0x002C jmp SPM_RDY ; Store Program Memory Ready Handler
;
.org 0x3800/0x7800
0x3800/0x7801RESET:ldir16,high(RAMEND); Main program start
0x3801/0x7801 out SPH,r16 ; Set Stack Pointer to top of RAM
0x3802/0x7802 ldi r16,low(RAMEND)
0x3803/0x7803 out SPL,r16
0x3804/0x7804 sei ; Enable interrupts
0x3805/0x7805 <instr> xxx
When the BOOTRST Fuse is programmed, the Boot section size set to 4K bytes and the IVSEL
bit in the MCUCR Register is set before any interrupts are enabled, the most typical and general
program setup for the Reset and Interrupt Vector Addresses is:
Address Labels Code Comments
;
.org 0x3800/0x7800
0x3800/0x7800 jmp RESET ; Reset handler
0x3802/0x7802 jmp EXT_INT0 ; IRQ0 Handler
0x3804/0x7804 jmp PCINT0 ; PCINT0 Handler
... ... ... ;
0x382C/0x782C jmp SPM_RDY ; Store Program Memory Ready Handler
;
0x382E/0x782ERESET:ldir16,high(RAMEND); Main program start
0x382F/0x782F out SPH,r16 ; Set Stack Pointer to top of RAM
0x3830/0x7830 ldi r16,low(RAMEND)
0x3831/0x7831 out SPL,r16
0x3832/0x7832 sei ; Enable interrupts
0x3833/0x7833 <instr> xxx
11.1.1 Moving Interrupts Between Application and Boot Space
The MCU Control Register controls the placement of the Interrupt Vector table.
11.2 Register Description
11.2.1 MCUCR – MCU Control Register
• Bit 1 – IVSEL: Interrupt Vector Select
When the IVSEL bit is cleared (zero), the Interrupt Vectors are placed at the start of the Flash
memory. When this bit is set (one), the Interrupt Vectors are moved to the beginning of the Boot
Loader section of the Flash. The actual address of the start of the Boot Flash Section is deter-
mined by the BOOTSZ Fuses. Refer to the section “Boot Loader Support – Read-While-Write
Bit 76543210
0x35 (0x55) JTD – – PUD –– IVSEL IVCE MCUCR
Read/Write R/W R R R/W R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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Self-Programming” on page 278 for details. To avoid unintentional changes of Interrupt Vector
tables, a special write procedure must be followed to change the IVSEL bit:
1. Write the Interrupt Vector Change Enable (IVCE) bit to one.
2. Within four cycles, write the desired value to IVSEL while writing a zero to IVCE.
Interrupts will automatically be disabled while this sequence is executed. Interrupts are disabled
in the cycle IVCE is set, and they remain disabled until after the instruction following the write to
IVSEL. If IVSEL is not written, interrupts remain disabled for four cycles. The I-bit in the Status
Register is unaffected by the automatic disabling.
Note: If Interrupt Vectors are placed in the Boot Loader section and Boot Lock bit BLB02 is programmed,
interrupts are disabled while executing from the Application section. If Interrupt Vectors are placed
in the Application section and Boot Lock bit BLB12 is programed, interrupts are disabled while
executing from the Boot Loader section. Refer to the section “Boot Loader Support – Read-While-
Write Self-Programming” on page 278 for details on Boot Lock bits.
• Bit 0 – IVCE: Interrupt Vector Change Enable
The IVCE bit must be written to logic one to enable change of the IVSEL bit. IVCE is cleared by
hardware four cycles after it is written or when IVSEL is written. Setting the IVCE bit will disable
interrupts, as explained in the IVSEL description above. See Code Example below.
Assembly Code Example
Move_interrupts:
;Get MCUCR
in r16, MCUCR
mov r17, r16
; Enable change of Interrupt Vectors
ori r16, (1<<IVCE)
out MCUCR, r16
; Move interrupts to Boot Flash section
ori r17, (1<<IVSEL)
out MCUCR, r17
ret
C Code Example
void Move_interrupts(void)
{
/* Enable change of Interrupt Vectors */
MCUCR |= (1<<IVCE);
/* Move interrupts to Boot Flash section */
MCUCR |= (1<<IVSEL);
}
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12. External Interrupts
The External Interrupts are triggered by the INT0 pin or any of the PCINT30..0 pins. Observe
that, if enabled, the interrupts will trigger even if the INT0 or PCINT30..0 pins are configured as
outputs. This feature provides a way of generating a software interrupt. The pin change interrupt
PCI1 will trigger if any enabled PCINT15..8 pin toggles. Pin change interrupts PCI0 will trigger if
any enabled PCINT7..0 pin toggles. The PCMSK3, PCMSK2, PCMSK1, and PCMSK0 Registers
control which pins contribute to the pin change interrupts. Pin change interrupts on PCINT30..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 External Interrupt Control Register A – EICRA. 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 “Clock Systems and their Distribution” on page 26. 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 inter-
rupt will be generated. The start-up time is defined by the SUT and CKSEL Fuses as described
in “System Clock and Clock Options” on page 26.
12.1 Pin Change Interrupt Timing
An example of timing of a pin change interrupt is shown in Figure 12-1.
Figure 12-1. Pin Change Interrupt
clk
PCINT(n)
pin_lat
pin_sync
pcint_in_(n)
pcint_syn
pcint_setflag
PCIF
PCINT(0)
pin_sync
pcint_syn
pin_lat
D Q
LE
pcint_setflag
PCIF
clk
clk
PCINT(0) in PCMSK(x)
pcint_in_(0) 0
x
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12.2 Register Description
12.2.1 EICRA – External Interrupt Control Register A
The External Interrupt Control Register A contains control bits for interrupt sense control.
• Bit 1, 0 – ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0
The External Interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the corre-
sponding interrupt mask are set. The level and edges on the external INT0 pin that activate the
interrupt are defined in Table 12-1. 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.
12.2.2 External Interrupt Mask Register – EIMSK
• Bit 7 – PCIE3: Pin Change Interrupt Enable 3
When the PCIE3 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin
change interrupt 3 is enabled. Any change on any enabled PCINT30..24 pin will cause an inter-
rupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCINT3
Interrupt Vector. PCINT30..24 pins are enabled individually by the PCMSK3 Register.
This bit is reserved bit in ATmega329/649 and should always be written to zero.
• Bit 6 – PCIE2: Pin Change Interrupt Enable 2
When the PCIE2 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin
change interrupt 2 is enabled. Any change on any enabled PCINT23..16 pin will cause an inter-
rupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCINT2
Interrupt Vector. PCINT23..16 pins are enabled individually by the PCMSK2 Register.
This bit is reserved bit in ATmega329/649 and should always be written to zero.
Bit 76543210
(0x69) – – – – – – ISC01 ISC00 EICRA
Read/WriteRRRRRRR/WR/W
Initial Value00000000
Table 12-1. 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
PCIE3 PCIE2 PCIE1 PCIE0 – – –INT0EIMSK
Read/Write R/W R/W R/W R/W R R R R/W
Initial Value 0 0 0 0 0 0 0 0
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• 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 PCINT15..8 pin will cause an inter-
rupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCINT1
Interrupt Vector. PCINT15..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 PCINT0 Inter-
rupt Vector. PCINT7..0 pins are enabled individually by the PCMSK0 Register.
• Bit 0 – INT0: External Interrupt Request 0 Enable
When the INT0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the exter-
nal 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.
12.2.3 EIFR – External Interrupt Flag Register
• Bit 7 – PCIF3: Pin Change Interrupt Flag 3
When a logic change on any PCINT30..24 pin triggers an interrupt request, PCIF3 becomes set
(one). If the I-bit in SREG and the PCIE3 bit in EIMSK are set (one), the MCU will jump to the
corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alter-
natively, the flag can be cleared by writing a logical one to it.
This bit is reserved bit in ATmega329/649 and will always be read as zero.
• Bit 6 – PCIF2: Pin Change Interrupt Flag 2
When a logic change on any PCINT24..16 pin triggers an interrupt request, PCIF2 becomes set
(one). If the I-bit in SREG and the PCIE2 bit in EIMSK are set (one), the MCU will jump to the
corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alter-
natively, the flag can be cleared by writing a logical one to it.
This bit is reserved bit in ATmega329/649 and will always be read as zero.
• Bit 5 – PCIF1: Pin Change Interrupt Flag 1
When a logic change on any PCINT15..8 pin triggers an interrupt request, PCIF1 becomes set
(one). If the I-bit in SREG and the PCIE1 bit in EIMSK are set (one), the MCU will jump to the
corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alter-
natively, the flag can be cleared by writing a logical one to it.
Bit 76543210
0x1C (0x3C) PCIF3 PCIF2 PCIF1 PCIF0 – – – INTF0 EIFR
Read/Write R/W R/W R/W R/W R R R R/W
Initial Value 0 0 0 0 0 0 0 0
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• Bit 4 – PCIF0: Pin Change Interrupt Flag 0
When a logic change on any PCINT7..0 pin triggers an interrupt request, PCIF0 becomes set
(one). If the I-bit in SREG and the PCIE0 bit in EIMSK are set (one), the MCU will jump to the
corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alter-
natively, the flag can be cleared by writing a logical one to it.
• Bit 0 – INTF0: External Interrupt Flag 0
When an edge or logic change on the INT0 pin triggers an interrupt request, INTF0 becomes set
(one). If the I-bit in SREG and the INT0 bit in EIMSK are set (one), the MCU will jump to the cor-
responding 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.
12.2.4 PCMSK3 – Pin Change Mask Register 3(1)
• Bit 6:0 – PCINT30..24: Pin Change Enable Mask 30..24
Each PCINT30..24-bit selects whether pin change interrupt is enabled on the corresponding I/O
pin. If PCINT30..24 is set and the PCIE3 bit in EIMSK is set, pin change interrupt is enabled on
the corresponding I/O pin. If PCINT30..24 is cleared, pin change interrupt on the corresponding
I/O pin is disabled.
12.2.5 PCMSK2 – Pin Change Mask Register 2(1)
• Bit 7:0 – PCINT23:16: Pin Change Enable Mask 23:16
Each PCINT23:16 bit selects whether pin change interrupt is enabled on the corresponding I/O
pin. If PCINT23:16 is set and the PCIE2 bit in EIMSK is set, pin change interrupt is enabled on
the corresponding I/O pin. If PCINT23:16 is cleared, pin change interrupt on the corresponding
I/O pin is disabled.
Note: 1. PCMSK3 and PCMSK2 are only present in ATmega3290/6490.
Bit 76543210
(0x73) – PCINT30 PCINT29 PCINT28 PCINT27 PCINT26 PCINT25 PCINT24 PCMSK3
Read/Write R R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
(0x6D) PCINT23 PCINT22 PCINT21 PCINT20 PCINT19 PCINT18 PCINT17 PCINT16 PCMSK2
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial
Value
00000000
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12.2.6 PCMSK1 – Pin Change Mask Register 1
• Bit 7:0 – PCINT15:8: Pin Change Enable Mask 15:8
Each PCINT15:8-bit selects whether pin change interrupt is enabled on the corresponding I/O
pin. If PCINT15:8 is set and the PCIE1 bit in EIMSK is set, pin change interrupt is enabled on the
corresponding I/O pin. If PCINT15:8 is cleared, pin change interrupt on the corresponding I/O
pin is disabled.
12.2.7 PCMSK0 – Pin Change Mask Register 0
• Bit 7:0 – PCINT7:0: Pin Change Enable Mask 7:0
Each PCINT7:0 bit selects whether pin change interrupt is enabled on the corresponding I/O pin.
If PCINT7:0 is set and the PCIE0 bit in EIMSK is set, pin change interrupt is enabled on the cor-
responding I/O pin. If PCINT7:0 is cleared, pin change interrupt on the corresponding I/O pin is
disabled.
Bit 76543210
(0x6C) PCINT15 PCINT14 PCINT13 PCINT12 PCINT11 PCINT10 PCINT9 PCINT8 PCMSK1
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
(0x6B) 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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13. I/O-Ports
13.1 Introduction
All AVR ports have true Read-Modify-Write functionality when used as general digital I/O ports.
This means that the direction of one port pin can be changed without unintentionally changing
the direction of any other pin with the SBI and CBI instructions. The same applies when chang-
ing 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. Port B has a higher pin driver strength than the other ports, but all the pin drivers are
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 13-1. Refer to “Electrical Characteristics” on page 326 for
a complete list of parameters. If exceeding the pin voltage “Absolute Maximum Ratings”, result-
ing currents can harm the device if not limited accordingly. For segment pins used as general
I/O, the same situation can also influence the LCD voltage level.
Figure 13-1. I/O Pin Equivalent Schematic
All registers and bit references in this section are written in general form. A lower case “x” repre-
sents 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 Regis-
ters and bit locations are listed in “Register Description” on page 87.
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 correspond-
ing 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 “Ports as General Digital I/O” on page
60. 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 “Alternate Port
Cpin
Logic
Rpu
See Figure
"General Digital I/O" for
Details
Pxn
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Functions” on page 65. Refer to the individual module sections for a full description of the alter-
nate 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.
13.2 Ports as General Digital I/O
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 13-2 shows a func-
tional description of one I/O-port pin, here generically called Pxn.
Figure 13-2. 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.
13.2.1 Configuring the Pin
Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in “Register
Description” on page 87, 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
clk
RPx
RRx
RDx
WDx
PUD
SYNCHRONIZER
WDx: WRITE DDRx
WRx: WRITE PORTx
RRx: READ PORTx REGISTER
RPx: READ PORTx PIN
PUD: PULLUP DISABLE
clk
I/O
: I/O CLOCK
RDx: READ DDRx
D
L
Q
Q
RESET
RESET
Q
Q
D
Q
Q D
CLR
PORTxn
Q
QD
CLR
DDxn
PINxn
DATA BUS
SLEEP
SLEEP: SLEEP CONTROL
Pxn
I/O
WPx
0
1
WRx
WPx: WRITE PINx REGISTER
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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).
13.2.2 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.
13.2.3 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 accept-
able, as a high-impedant environment will not notice the difference between a strong high driver
and a pull-up. If this is not the case, the PUD bit in the MCUCR Register can be set to disable all
pull-ups in all ports.
Switching between input with pull-up and output low generates the same problem. The user
must use either the tri-state ({DDxn, PORTxn} = 0b00) or the output high state ({DDxn, PORTxn}
= 0b11) as an intermediate step.
Table 13-1 summarizes the control signals for the pin value.
13.2.4 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 13-2, the PINxn Register bit and the preceding latch con-
stitute 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 13-3 shows a timing dia-
gram of the synchronization when reading an externally applied pin value. The maximum and
minimum propagation delays are denoted tpd,max and tpd,min respectively.
Table 13-1. 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)
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Figure 13-3. Synchronization when Reading an Externally Applied Pin value
XXX in r17, PINx
0x00 0xFF
INSTRUCTIONS
SYNC LATCH
PINxn
r17
XXX
SYSTEM CLK
t
pd, max
t
pd, min
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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 indi-
cated 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.
When reading back a software assigned pin value, a nop instruction must be inserted as indi-
cated in Figure 13-4. 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 1 system clock period.
Figure 13-4. Synchronization when Reading a Software Assigned Pin Value
The following code example shows how to set port B pins 0 and 1 high, 2 and 3 low, and define
the port pins from 4 to 7 as input with pull-ups assigned to port pins 6 and 7. The resulting pin
values are read back again, but as previously discussed, a nop instruction is included to be able
to read back the value recently assigned to some of the pins.
out PORTx, r16 nop in r17, PINx
0xFF
0x00 0xFF
SYSTEM CLK
r16
INSTRUCTIONS
SYNC LATCH
PINxn
r17
t
pd
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Note: 1. For the assembly program, two temporary registers are used to minimize the time from pull-
ups are set on pins 0, 1, 6, and 7, until the direction bits are correctly set, defining bit 2 and 3
as low and redefining bits 0 and 1 as strong high drivers.
13.2.5 Digital Input Enable and Sleep Modes
As shown in Figure 13-2, 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 “Alternate Port Functions” on page 65.
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.
13.2.6 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, float-
Assembly Code Example(1)
...
; Define pull-ups and set outputs high
; Define directions for port pins
ldi r16,(1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0)
ldi r17,(1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0)
out PORTB,r16
out DDRB,r17
; Insert nop for synchronization
nop
; Read port pins
in r16,PINB
...
C Code Example
unsigned char i;
...
/* Define pull-ups and set outputs high */
/* Define directions for port pins */
PORTB = (1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0);
DDRB = (1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0);
/* Insert nop for synchronization*/
__no_operation();
/* Read port pins */
i = PINB;
...
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ing inputs should be avoided to reduce current consumption in all other modes where the digital
inputs are enabled (Reset, Active mode and Idle mode).
The simplest method to ensure a defined level of an unused pin, is to enable the internal pull-up.
In this case, the pull-up will be disabled during reset. If low power consumption during reset is
important, it is recommended to use an external pull-up or pull-down. Connecting unused pins
directly to VCC or GND is not recommended, since this may cause excessive currents if the pin is
accidentally configured as an output.
13.3 Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. Figure 13-5
shows how the port pin control signals from the simplified Figure 13-2 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.
Figure 13-5. 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.
clk
RPx
RRx
WRx
RDx
WDx
PUD
SYNCHRONIZER
WDx: WRITE DDRx
WRx: WRITE PORTx
RRx: READ PORTx REGISTER
RPx: READ PORTx PIN
PUD: PULLUP DISABLE
clk
I/O
: I/O CLOCK
RDx: READ DDRx
D
L
Q
Q
SET
CLR
0
1
0
1
0
1
DIxn
AIOxn
DIEOExn
PVOVxn
PVOExn
DDOVxn
DDOExn
PUOExn
PUOVxn
PUOExn: Pxn PULL-UP OVERRIDE ENABLE
PUOVxn: Pxn PULL-UP OVERRIDE VALUE
DDOExn: Pxn DATA DIRECTION OVERRIDE ENABLE
DDOVxn: Pxn DATA DIRECTION OVERRIDE VALUE
PVOExn: Pxn PORT VALUE OVERRIDE ENABLE
PVOVxn: Pxn PORT VALUE OVERRIDE VALUE
DIxn: DIGITAL INPUT PIN n ON PORTx
AIOxn: ANALOG INPUT/OUTPUT PIN n ON PORTx
RESET
RESET
Q
QD
CLR
Q
QD
CLR
Q
Q
D
CLR
PINxn
PORTxn
DDxn
DATA B U S
0
1
DIEOVxn
SLEEP
DIEOExn: Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE
DIEOVxn: Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE
SLEEP: SLEEP CONTROL
Pxn
I/O
0
1
PTOExn
WPx
PTOExn: Pxn, PORT TOGGLE OVERRIDE ENABLE
WPx: WRITE PINx
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Table 13-2 summarizes the function of the overriding signals. The pin and port indexes from Fig-
ure 13-5 are not shown in the succeeding tables. The overriding signals are generated internally
in the modules having the alternate function.
The following subsections shortly describe the alternate functions for each port, and relate the
overriding signals to the alternate function. Refer to the alternate function description for further
details.
Some pins are connected to different LCS segments on ATmega3290/6490 and
ATmega3290/6490. See pinout on “Pinout ATmega3290/6490” on page 2 and “Pinout
ATmega329/649” on page 3 for details.
Table 13-2. 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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13.3.1 Alternate Functions of Port A
The Port A has an alternate function as COM0:3 and SEG0:3 for the LCD Controller.
Table 13-4 and Table 13-5 relates the alternate functions of Port A to the overriding signals
shown in Figure 13-5 on page 65.
Table 13-3. Port A Pins Alternate Functions
Port Pin Alternate Function
PA7 SEG (LCD Front Plane 3)
PA6 SEG (LCD Front Plane 2)
PA5 SEG (LCD Front Plane 1)
PA4 SEG (LCD Front Plane 0)
PA3 COM (LCD Back Plane 3)
PA2 COM (LCD Back Plane 2)
PA1 COM (LCD Back Plane 1)
PA0 COM (LCD Back Plane 0)
Table 13-4. Overriding Signals for Alternate Functions in PA7..PA4
Signal
Name PA7/SEG3 PA6/SEG2 PA5/SEG1 PA4/SEG0
PUOE LCDENLCDENLCDENLCDEN
PUOV0000
DDOE LCDENLCDENLCDENLCDEN
DDOV 0 0 0 0
PVOE0000
PVOV0000
PTOE––––
DIEOE LCDENLCDENLCDENLCDEN
DIEOV0000
DI––––
AIO LCDSEG LCDSEG LCDSEG LCDSEG
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13.3.2 Alternate Functions of Port B
The Port B pins with alternate functions are shown in Table 13-6.
The alternate pin configuration is as follows:
• OC2A/PCINT15, Bit 7
OC2, Output Compare Match A output: The PB7 pin can serve as an external output for the
Timer/Counter2 Output Compare A. The pin has to be configured as an output (DDB7 set (one))
to serve this function. The OC2A pin is also the output pin for the PWM mode timer function.
Table 13-5. Overriding Signals for Alternate Functions in PA3..PA0
Signal
Na me PA3/ COM3 PA2/C OM2 PA 1/ COM1 PA0/C OM0
PUOE LCDEN •
(LCDMUX)
LCDEN •
(LCDMUX)
LCDEN •
(LCDMUX)
LCDEN
PUOV0000
DDOE LCDEN •
(LCDMUX)
LCDEN •
(LCDMUX)
LCDEN •
(LCDMUX)
LCDEN
DDOV 0 0 0 0
PVOE0000
PVOV0000
PTOE––––
DIEOE LCDEN •
(LCDMUX)
LCDEN •
(LCDMUX)
LCDEN •
(LCDMUX)
LCDEN
DIEOV0000
DI––––
AIOCOM3COM2COM1COM0
Table 13-6. Port B Pins Alternate Functions
Port Pin Alternate Functions
PB7 OC2A/PCINT15 (Output Compare and PWM Output A for Timer/Counter2 or
Pin Change Interrupt15).
PB6 OC1B/PCINT14 (Output Compare and PWM Output B for Timer/Counter1 or
Pin Change Interrupt14).
PB5 OC1A/PCINT13 (Output Compare and PWM Output A for Timer/Counter1 or
Pin Change Interrupt13).
PB4 OC0A/PCINT12 (Output Compare and PWM Output A for Timer/Counter0 or
Pin Change Interrupt12).
PB3 MISO/PCINT11 (SPI Bus Master Input/Slave Output or Pin Change
Interrupt11).
PB2 MOSI/PCINT10 (SPI Bus Master Output/Slave Input or Pin Change
Interrupt10).
PB1 SCK/PCINT9 (SPI Bus Serial Clock or Pin Change Interrupt9).
PB0 SS/PCINT8 (SPI Slave Select input or Pin Change Interrupt8).
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PCINT15, Pin Change Interrupt source 15: The PB7 pin can serve as an external interrupt
source.
• OC1B/PCINT14, Bit 6
OC1B, Output Compare Match B output: The PB6 pin can serve as an external output for the
Timer/Counter1 Output Compare B. The pin has to be configured as an output (DDB6 set (one))
to serve this function. The OC1B pin is also the output pin for the PWM mode timer function.
PCINT14, Pin Change Interrupt Source 14: The PB6 pin can serve as an external interrupt
source.
• OC1A/PCINT13, Bit 5
OC1A, Output Compare Match A output: The PB5 pin can serve as an external output for the
Timer/Counter1 Output Compare A. The pin has to be configured as an output (DDB5 set (one))
to serve this function. The OC1A pin is also the output pin for the PWM mode timer function.
PCINT13, Pin Change Interrupt Source 13: The PB5 pin can serve as an external interrupt
source.
• OC0A/PCINT12, Bit 4
OC0A, Output Compare Match A output: The PB4 pin can serve as an external output for the
Timer/Counter0 Output Compare A. The pin has to be configured as an output (DDB4 set (one))
to serve this function. The OC0A pin is also the output pin for the PWM mode timer function.
PCINT12, Pin Change Interrupt Source 12: The PB4 pin can serve as an external interrupt
source.
• MISO/PCINT11 – Port B, Bit 3
MISO: Master Data input, Slave Data output pin for SPI. When the SPI is enabled as a Master,
this pin is configured as an input regardless of the setting of DDB3. When the SPI is enabled as
a Slave, the data direction of this pin is controlled by DDB3. When the pin is forced to be an
input, the pull-up can still be controlled by the PORTB3 bit.
PCINT11, Pin Change Interrupt Source 11: The PB3 pin can serve as an external interrupt
source.
• MOSI/PCINT10 – Port B, Bit 2
MOSI: SPI Master Data output, Slave Data input for SPI. When the SPI is enabled as a Slave,
this pin is configured as an input regardless of the setting of DDB2. When the SPI is enabled as
a Master, the data direction of this pin is controlled by DDB2. When the pin is forced to be an
input, the pull-up can still be controlled by the PORTB2 bit.
PCINT10, Pin Change Interrupt Source 10: The PB2 pin can serve as an external interrupt
source.
• SCK/PCINT9 – Port B, Bit 1
SCK: Master Clock output, Slave Clock input pin for SPI. When the SPI is enabled as a Slave,
this pin is configured as an input regardless of the setting of DDB1. When the SPI is enabled as
a Master, the data direction of this pin is controlled by DDB1. When the pin is forced to be an
input, the pull-up can still be controlled by the PORTB1 bit.
PCINT9, Pin Change Interrupt Source 9: The PB1 pin can serve as an external interrupt source.
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•SS/PCINT8 – Port B, Bit 0
SS: Slave Port Select input. When the SPI is enabled as a Slave, this pin is configured as an
input regardless of the setting of DDB0. As a Slave, the SPI is activated when this pin is driven
low. When the SPI is enabled as a Master, the data direction of this pin is controlled by DDB0.
When the pin is forced to be an input, the pull-up can still be controlled by the PORTB0 bit
PCINT8, Pin Change Interrupt Source 8: The PB0 pin can serve as an external interrupt source.
Table 13-7 and Table 13-8 relate the alternate functions of Port B to the overriding signals
shown in Figure 13-5 on page 65. SPI MSTR INPUT and SPI SLAVE OUTPUT constitute the
MISO signal, while MOSI is divided into SPI MSTR OUTPUT and SPI SLAVE INPUT.
Table 13-7. Overriding Signals for Alternate Functions in PB7:PB4
Signal
Name
PB7/OC2A/
PCINT15
PB6/OC1B/
PCINT14
PB5/OC1A/
PCINT13
PB4/OC0A/
PCINT12
PUOE0000
PUOV0000
DDOE 0 0 0 0
DDOV 0 0 0 0
PVOE OC2A ENABLE OC1B ENABLE OC1A ENABLE OC0A ENABLE
PVOV OC2A OC1B OC1A OC0A
PTOE––––
DIEOE PCINT15 •
PCIE1
PCINT14 •
PCIE1
PCINT13 •
PCIE1
PCINT12 •
PCIE1
DIEOV1111
DI PCINT15 INPUT PCINT14 INPUT PCINT13 INPUT PCINT12 INPUT
AIO––––
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13.3.3 Alternate Functions of Port C
The Port C has an alternate function as SEG for the LCD Controller.
The alternate pin configuration is as follows:
• SEG – Port D, Bit 7:0
SEG, LCD front plane 5/5, 6/6, 11/7-16/12.
Table 13-10 and Table 13-11 relate the alternate functions of Port C to the overriding signals
shown in Figure 13-5 on page 65.
Table 13-8. Overriding Signals for Alternate Functions in PB3:PB0
Signal
Name
PB3/MISO/
PCINT11
PB2/MOSI/
PCINT10
PB1/SCK/
PCINT9
PB0/SS/
PCINT8
PUOE SPE • MSTR SPE • MSTR SPE • MSTR SPE • MSTR
PUOV PORTB3 • PUD PORTB2 • PUD PORTB1 • PUD PORTB0 • PUD
DDOE SPE • MSTR SPE • MSTR SPE • MSTR SPE • MSTR
DDOV 0 0 0 0
PVOE SPE • MSTR SPE • MSTR SPE • MSTR 0
PVOV SPI SLAVE
OUTPUT
SPI MSTR
OUTPUT
SCK OUTPUT 0
PTOE––––
DIEOE PCINT11 •
PCIE1
PCINT10 •
PCIE1
PCINT9 • PCIE1 PCINT8 • PCIE1
DIEOV1111
DI PCINT11 INPUT
SPI MSTR
INPUT
PCINT10 INPUT
SPI SLAVE
INPUT
PCINT9 INPUT
SCK INPUT
PCINT8 INPUT
SPI SS
AIO––––
Table 13-9. Port C Pins Alternate Functions (SEG refers to 100-pin/64-pin pinout)
Port Pin Alternate Function
PC7 SEG (LCD Front Plane 5/5)
PC6 SEG (LCD Front Plane 6/6)
PC5 SEG (LCD Front Plane 11/7)
PC4 SEG (LCD Front Plane 12/8)
PC3 SEG (LCD Front Plane 13/9)
PC2 SEG (LCD Front Plane14/10)
PC1 SEG (LCD Front Plane 15/11)
PC0 SEG (LCD Front Plane 16/12)
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Table 13-10. Overriding Signals for Alternate Functions in PC7:PC4
Signal
Name PC7/SEG5 PC6/SEG6 PC5/SEG(11/7) PC4/SEG(12/8)
PUOE LCDENLCDENLCDENLCDEN
PUOV0000
DDOE LCDENLCDENLCDENLCDEN
DDOV 0 0 0 0
PVOE0000
PVOV0000
PTOE––––
DIEOE LCDENLCDENLCDENLCDEN
DIEOV0000
DI––––
AIO LCDSEG LCDSEG LCDSEG LCDSEG
Table 13-11. Overriding Signals for Alternate Functions in PC3:PC0
Signal
Name PC3/SEG(13/9) PC2/SEG(14/10) PC1/SEG(15/11) PC0/SEG(16/12)
PUOE LCDENLCDENLCDENLCDEN
PUOV0000
DDOE LCDENLCDENLCDENLCDEN
DDOV 0 0 0 0
PVOE0000
PVOV0000
PTOE––––
DIEOE LCDENLCDENLCDENLCDEN
DIEOV0000
DI––––
AIO LCDSEG LCDSEG LCDSEG LCDSEG
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13.3.4 Alternate Functions of Port D
The Port D pins with alternate functions are shown in Table 13-12.
The alternate pin configuration is as follows:
• SEG – Port D, Bit 7:2
SEG, LCD front plane 19/15-24/20.
•INT0
/SEG – Port D, Bit 1
INT0, External Interrupt Source 0. The PD1 pin can serve as an external interrupt source to the
MCU.
SEG, LCD front plane 25/21.
• ICP1/SEG – Port D, Bit 0
ICP1 – Input Capture pin1: The PD0 pin can act as an Input Capture pin for Timer/Counter1.
SEG, LCD front plane 26/22
Table 13-13 and Table 13-14 relates the alternate functions of Port D to the overriding signals
shown in Figure 13-5 on page 65.
Table 13-12. Port D Pins Alternate Functions (SEG refers to 100-pin/64-pin pinout)
Port Pin Alternate Function
PD7 SEG (LCD front plane 19/15)
PD6 SEG (LCD front plane 20/16)
PD5 SEG (LCD front plane 21/17)
PD4 SEG (LCD front plane 22/18)
PD3 SEG (LCD front plane 23/19)
PD2 SEG (LCD front plane 24/20)
PD1 INT0/SEG (External Interrupt0 Input or LCD front plane 25/21)
PD0 ICP1/SEG (Timer/Counter1 Input Capture pin or LCD front plane 26/22)
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Table 13-13. Overriding Signals for Alternate Functions PD7:PD4
Signal
Name PD7/SEG(19/15) PD6/SEG(20/16) PD5/SEG(21/17) PD4/SEG(22/18)
PUOE LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
PUOV0000
DDOE LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
DDOV 0 0 0 0
PVOE0000
PVOV0000
PTOE––––
DIEOE LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
DIEOV0000
DI––––
AIO LCDSEG LCDSEG LCDSEG LCDSEG
Table 13-14. Overriding Signals for Alternate Functions in PD3:PD0
Signal
Name PD3/SEG(23/19) PD2/SEG(24/20)
PD1/INT0/
SEG(25/21)
PD0/ICP1/
SEG(26/22)
PUOE LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
PUOV0000
DDOE LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
DDOV 0 0 0 0
PVOE0000
PVOV0000
PTOE––––
DIEOE LCDEN •
(LCDPM)
LCDEN •
(LCDPM)
LCDEN +
(INT0 ENABLE)
LCDEN •
(LCDPM)
DIEOV 0 0 LCDEN •
(INT0 ENABLE)
0
DI––INT0 INPUT ICP1 INPUT
AIO LCDSEG LCDSEG LCDSEG LCDSEG
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13.3.5 Alternate Functions of Port E
The Port E pins with alternate functions are shown in Table 13-15.
• PCINT7 – Port E, Bit 7
PCINT7, Pin Change Interrupt Source 7: The PE7 pin can serve as an external interrupt source.
CLKO, Divided System Clock: The divided system clock can be output on the PE7 pin. The
divided system clock will be output if the CKOUT Fuse is programmed, regardless of the
PORTE7 and DDE7 settings. It will also be output during reset.
• DO/PCINT6 – Port E, Bit 6
DO, Universal Serial Interface Data output.
PCINT6, Pin Change Interrupt Source 6: The PE6 pin can serve as an external interrupt source.
• DI/SDA/PCINT5 – Port E, Bit 5
DI, Universal Serial Interface Data input.
SDA, Two-wire Serial Interface Data:
PCINT5, Pin Change Interrupt Source 5: The PE5 pin can serve as an external interrupt source.
• USCK/SCL/PCINT4 – Port E, Bit 4
USCK, Universal Serial Interface Clock.
SCL, Two-wire Serial Interface Clock.
PCINT4, Pin Change Interrupt Source 4: The PE4 pin can serve as an external interrupt source.
• AIN1/PCINT3 – Port E, Bit 3
AIN1 – Analog Comparator Negative input. This pin is directly connected to the negative input of
the Analog Comparator.
PCINT3, Pin Change Interrupt Source 3: The PE3 pin can serve as an external interrupt source.
Table 13-15. Port E Pins Alternate Functions
Port Pin Alternate Function
PE7 PCINT7 (Pin Change Interrupt7)
CLKO (Divided System Clock)
PE6 DO/PCINT6 (USI Data Output or Pin Change Interrupt6)
PE5 DI/SDA/PCINT5 (USI Data Input or TWI Serial DAta or Pin Change Interrupt5)
PE4 USCK/SCL/PCINT4 (USART0 External Clock Input/Output or TWI Serial Clock
or Pin Change Interrupt4)
PE3 AIN1/PCINT3 (Analog Comparator Negative Input or Pin Change Interrupt3)
PE2 XCK/AIN0/ PCINT2 (USART0 External Clock or Analog Comparator Positive
Input or Pin Change Interrupt2)
PE1 TXD/PCINT1 (USART0 Transmit Pin or Pin Change Interrupt1)
PE0 RXD/PCINT0 (USART0 Receive Pin or Pin Change Interrupt0)
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• XCK/AIN0/PCINT2 – Port E, Bit 2
XCK, USART0 External Clock. The Data Direction Register (DDE2) controls whether the clock is
output (DDE2 set) or input (DDE2 cleared). The XCK pin is active only when the USART0 oper-
ates in synchronous mode.
AIN0 – Analog Comparator Positive input. This pin is directly connected to the positive input of
the Analog Comparator.
PCINT2, Pin Change Interrupt Source 2: The PE2 pin can serve as an external interrupt source.
• TXD/PCINT1 – Port E, Bit 1
TXD0, UART0 Transmit pin.
PCINT1, Pin Change Interrupt Source 1: The PE1 pin can serve as an external interrupt source.
• RXD/PCINT0 – Port E, Bit 0
RXD, USART0 Receive pin. Receive Data (Data input pin for the USART0). When the USART0
Receiver is enabled this pin is configured as an input regardless of the value of DDE0. When the
USART0 forces this pin to be an input, a logical one in PORTE0 will turn on the internal pull-up.
PCINT0, Pin Change Interrupt Source 0: The PE0 pin can serve as an external interrupt source.
Table 13-16 and Table 13-17 relates the alternate functions of Port E to the overriding signals
shown in Figure 13-5 on page 65.
Note: 1. CKOUT is one if the CKOUT Fuse is programmed
Table 13-16. Overriding Signals for Alternate Functions PE7:PE4
Signal
Name PE7/PCINT7
PE6/DO/
PCINT6
PE5/DI/SDA/
PCINT5
PE4/USCK/SCL/
PCINT4
PUOE 0 0 USI_TWO-WIRE USI_TWO-WIRE
PUOV0000
DDOE CKOUT(1) 0 USI_TWO-WIRE USI_TWO-WIRE
DDOV 1 0 (SDA +
PORTE5) •
DDE5
(USI_SCL_HOL
D + PORTE4) •
DDE4
PVOE CKOUT(1) USI_THREE-
WIRE
USI_TWO-WIRE
• DDE5
USI_TWO-WIRE
• DDE4
PVOV clkI/O DO 0 0
PTOE – – 0 USITC
DIEOE PCINT7 • PCIE0 PCINT6 • PCIE0 (PCINT5 •
PCIE0) + USISIE
(PCINT4 •
PCIE0) + USISIE
DIEOV1111
DI PCINT7 INPUT PCINT6 INPUT DI/SDA INPUT
PCINT5 INPUT
USCKL/SCL
INPUT
PCINT4 INPUT
AIO––––
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Note: 1. AIN0D and AIN1D is described in “DIDR1 – Digital Input Disable Register 1” on page 210.
13.3.6 Alternate Functions of Port F
The Port F has an alternate function as analog input for the ADC as shown in Table 13-18. If
some Port F pins are configured as outputs, it is essential that these do not switch when a con-
version is in progress. This might corrupt the result of the conversion. If the JTAG interface is
enabled, the pull-up resistors on pins PF7(TDI), PF5(TMS) and PF4(TCK) will be activated even
if a reset occurs.
• TDI, ADC7 – Port F, Bit 7
ADC7, Analog to Digital Converter, Channel 7.
TDI, JTAG Test Data In: Serial input data to be shifted in to the Instruction Register or Data Reg-
ister (scan chains). When the JTAG interface is enabled, this pin can not be used as an I/O pin.
Table 13-17. Overriding Signals for Alternate Functions in PE3:PE0
Signal
Name
PE3/AIN1/
PCINT3
PE2/XCK/AIN0/
PCINT2
PE1/TXD/
PCINT1
PE0/RXD/PCINT
0
PUOE 0 XCK OUTPUT
ENABLE
TXENRXEN
PUOV 0 XCK 0 PORTE0 • PUD
DDOE 0 0 TXENRXEN
DDOV 0 0 1 0
PVOE 0 0 TXEN0
PVOV 0 0 TXD 0
PTOE––––
DIEOE (PCINT3 •
PCIE0) +
AIN1D(1)
(PCINT2 •
PCIE0) +
AIN0D(1)
PCINT1 • PCIE0 PCINT0 • PCIE0
DIEOV PCINT3 • PCIE0 PCINT2 • PCIE0 1 1
DI PCINT3 INPUT XCK/PCINT2
INPUT
PCINT1 INPUT RXD/PCINT0
INPUT
AIO AIN1 INPUT AIN0 INPUT – –
Table 13-18. Port F Pins Alternate Functions
Port Pin Alternate Function
PF7 ADC7/TDI (ADC input channel 7 or JTAG Test Data Input)
PF6 ADC6/TDO (ADC input channel 6 or JTAG Test Data Output)
PF5 ADC5/TMS (ADC input channel 5 or JTAG Test mode Select)
PF4 ADC4/TCK (ADC input channel 4 or JTAG Test ClocK)
PF3 ADC3 (ADC input channel 3)
PF2 ADC2 (ADC input channel 2)
PF1 ADC1 (ADC input channel 1)
PF0 ADC0 (ADC input channel 0)
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• TDO, ADC6 – Port F, Bit 6
ADC6, Analog to Digital Converter, Channel 6.
TDO, JTAG Test Data Out: Serial output data from Instruction Register or Data Register. When
the JTAG interface is enabled, this pin can not be used as an I/O pin. In TAP states that shift out
data, the TDO pin drives actively. In other states the pin is pulled high.
• TMS, ADC5 – Port F, Bit 5
ADC5, Analog to Digital Converter, Channel 5.
TMS, JTAG Test mode Select: This pin is used for navigating through the TAP-controller state
machine. When the JTAG interface is enabled, this pin can not be used as an I/O pin.
• TCK, ADC4 – Port F, Bit 4
ADC4, Analog to Digital Converter, Channel 4.
TCK, JTAG Test Clock: JTAG operation is synchronous to TCK. When the JTAG interface is
enabled, this pin can not be used as an I/O pin.
• ADC3 - ADC0 – Port F, Bit 3:0
Analog to Digital Converter, Channel 3-0.
Table 13-19. Overriding Signals for Alternate Functions in PF7:PF4
Signal
Name PF7/ADC7/TDI PF6/ADC6/TDO PF5/ADC5/TMS PF4/ADC4/TCK
PUOE JTAGENJTAGENJTAGENJTAGEN
PUOV1111
DDOE JTAGENJTAGENJTAGENJTAGEN
DDOV 0 SHIFT_IR +
SHIFT_DR
00
PVOE 0 JTAGEN00
PVOV 0 TDO 0 0
PTOE––––
DIEOE JTAGENJTAGENJTAGENJTAGEN
DIEOV0000
DI––––
AIO TDI
ADC7 INPUT
ADC6 INPUT TMS
ADC5 INPUT
TCK
ADC4 INPUT
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13.3.7 Alternate Functions of Port G
The alternate pin configuration is as follows:
Note: 1. Port G, PG5 is input only. Pull-up is always on.
See Table 27-3 on page 294 for RSTDISBL fuse.
The alternate pin configuration is as follows:
• RESET – Port G, Bit 5
RESET: External Reset input. When the RSTDISBL Fuse is programmed (‘0’), PG5 will function
as input with pull-up always on.
• T0/SEG – Port G, Bit 4
T0, Timer/Counter0 Counter Source.
SEG, LCD front plane 32/23.
• T1/SEG24 – Port G, Bit 3
T1, Timer/Counter1 Counter Source.
SEG, LCD front plane 33/24.
Table 13-20. Overriding Signals for Alternate Functions in PF3:PF0
Signal
Name PF3/ADC3 PF2/ADC2 PF1/ADC1 PF0/ADC0
PUOE0000
PUOV0000
DDOE 0 0 0 0
DDOV 0 0 0 0
PVOE0000
PVOV0000
PTOE––––
DIEOE0000
DIEOV0000
DI––––
AIO ADC3 INPUT ADC2 INPUT ADC1 INPUT ADC0 INPUT
Table 13-21. Port G Pins Alternate Functions (SEG refers to 100-pin/64-pin pinout)
Port Pin Alternate Function
PG5 RESET(1)
PG4 T0/SEG (Timer/Counter0 Clock Input or LCD Front Plane 32/23)
PG3 T1/SEG (Timer/Counter1 Clock Input or LCD Front Plane 33/24)
PG2 SEG (LCD Front Plane 4/4)
PG1 SEG (LCD Front Plane 17/13)
PG0 SEG (LCD Front Plane 18/14)
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• SEG – Port G, Bit 2
SEG, LCD front plane 4/4.
• SEG – Port G, Bit 1
SEG, Segment driver 17/13.
• SEG – Port G, Bit 0
SEG, LCD front plane 18/14.
Table 13-21 and Table 13-22 relates the alternate functions of Port G to the overriding signals
shown in Figure 13-5 on page 65.
Table 13-22. Overriding Signals for Alternate Functions in PG4
Signal
Name
PG4/T0/
SEG(32/23)
PUOE LCDEN
PUOV 0
DDOE LCDEN
DDOV 1
PVOE 0
PVOV 0
PTOE –
DIEOE LCDEN •
(LCDPM)
DIEOV 0
DI T0 INPUT
AIO LCDSEG
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13.3.8 Alternate Functions of Port H
Port H is only present in ATmega3290/6490. The alternate pin configuration is as follows:
The alternate pin configuration is as follows:
• PCINT23/SEG – Port H, Bit 7
PCINT23, Pin Change Interrupt Source 23: The PH7 pin can serve as an external interrupt
source.
SEG, LCD front plane 36.
• PCINT22/SEG – Port H, Bit 6
PCINT22, Pin Change Interrupt Source 22: The PH6 pin can serve as an external interrupt
source.
SEG, LCD front plane 37.
Table 13-23. Overriding Signals for Alternate Functions in PG3:0
Signal
Name
PG3/T1/
SEG(33/24) PG2/SEG(4/4) PG1/SEG(17/13) PG0/SEG(1814)
PUOE LCDENLCDENLCDENLCDEN
PUOV0000
DDOE LCDENLCDENLCDENLCDEN
DDOV 0 0 0 0
PVOE0000
PVOV0000
PTOE––––
DIEOE LCDEN •
(LCDPM)
LCDENLCDEN •
(LCDPM)
LCDEN •
(LCDPM)
DIEOV0000
DI T1 INPUT – – –
AIO LCDSEG LCDSEG LCDSEG LCDSEG
Table 13-24. Port H Pins Alternate Functions
Port Pin Alternate Function
PH7 PCINT23/SEG (Pin Change Interrupt23 or LCD Front Plane 36)
PH6 PCINT22/SEG (Pin Change Interrupt22 or LCD Front Plane 37)
PH5 PCINT21/SEG (Pin Change Interrupt21 or LCD Front Plane 38)
PH4 PCINT20/SEG (Pin Change Interrupt20 or LCD Front Plane 39)
PH3 PCINT19/SEG (Pin Change Interrupt19 or LCD Front Plane 7)
PH2 PCINT18/SEG (Pin Change Interrupt18 or LCD Front Plane 8)
PH1 PCINT17/SEG (Pin Change Interrupt17 or LCD Front Plane 9)
PH0 PCINT16/SEG (Pin Change Interrupt16 or LCD Front Plane 10)
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• PCINT21/SEG – Port H, Bit 5
PCINT21, Pin Change Interrupt Source 21: The PH5 pin can serve as an external interrupt
source.
SEG, LCD front plane 38.
• PCINT20/SEG – Port H, Bit 4
PCINT20, Pin Change Interrupt Source 20: The PH4 pin can serve as an external interrupt
source.
SEG, LCD front plane 39.
• PCINT19/SEG – Port H, Bit 3
PCINT19, Pin Change Interrupt Source 19: The PH3 pin can serve as an external interrupt
source.
SEG, LCD front plane 7.
• PCINT18/SEG – Port H, Bit 2
PCINT18, Pin Change Interrupt Source 18: The PH2 pin can serve as an external interrupt
source.
SEG, LCD front plane 8.
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• PCINT17/SEG – Port H, Bit 1
PCINT17, Pin Change Interrupt Source 17: The P1 pin can serve as an external interrupt
source.
SEG, LCD front plane 9.
• PCINT16/SEG – Port H, Bit 0
PCINT16, Pin Change Interrupt Source 16: The PH0 pin can serve as an external interrupt
source.
SEG, LCD front plane 10.
Table 13-25 and Table 13-26 relates the alternate functions of Port H to the overriding signals
shown in Figure 13-5 on page 65.
Table 13-25. Overriding Signals for Alternate Functions in PH7:4
Signal
Name
PH7/PCINT23/
SEG36
PH6/PCINT22/
SEG37
PH5/PCINT21/
SEG38
PH4/PCINT20/
SEG39
PUOE LCDENLCDENLCDENLCDEN
PUOV0000
DDOE LCDENLCDENLCDENLCDEN
DDOV 0 0 0 0
PVOE0000
PVOV0000
PTOE––––
DIEOE PCINT23 •
PCIE0 •LCDEN •
LCDPM
PCINT22 •
PCIE0 •LCDEN •
LCDPM
PCINT21 •
PCIE0 •LCDEN •
LCDPM
PCINT20 •
PCIE0 •LCDEN •
LCDPM
DIEOV
DI PCINT23 INPUT PCINT22 INPUT PCINT21 INPUT PCINT20 INPUT
AIO LCDSEG LCDSEG LCDSEG LCDSEG
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13.3.9 Alternate Functions of Port J
Port J is only present in ATmega3290/6490. The alternate pin configuration is as follows:
The alternate pin configuration is as follows:
• PCINT30/SEG – Port J, Bit 6
PCINT30, Pin Change Interrupt Source 30: The PE30 pin can serve as an external interrupt
source.
SEG, LCD front plane 27.
• PCINT29/SEG – Port J, Bit 5
PCINT29, Pin Change Interrupt Source 29: The PE29 pin can serve as an external interrupt
source.
SEG, LCD front plane28.
Table 13-26. Overriding Signals for Alternate Functions in PH3:0
Signal
Name
PH3/PCINT19/
SEG7
PH2/PCINT18/
SEG8
PH1/PCINT17/
SEG9
PH0/PCINT16/
SEG10
PUOE LCDENLCDENLCDENLCDEN
PUOV0000
DDOE LCDENLCDENLCDENLCDEN
DDOV 0 0 0 0
PVOE0000
PVOV0000
PTOE––––
DIEOE PCINT19 •
PCIE0 •LCDEN •
LCDPM
PCINT18 •
PCIE0 •LCDEN •
LCDPM
PCINT17 •
PCIE0 •LCDEN •
LCDPM
PCINT16 •
PCIE0 •LCDEN •
LCDPM
DIEOV
DI PCINT19 INPUT PCINT18 INPUT PCINT17 INPUT PCINT16 INPUT
AIO LCDSEG LCDSEG LCDSEG LCDSEG
Table 13-27. Port J Pins Alternate Functions
Port Pin Alternate Function
PJ6 PCINT30/SEG (Pin Change Interrupt30 or LCD Front Plane 27)
PJ5 PCINT29/SEG (Pin Change Interrupt29 or LCD Front Plane 28)
PJ4 PCINT28/SEG (Pin Change Interrupt28 or LCD Front Plane 29)
PJ3 PCINT27/SEG (Pin Change Interrupt27 or LCD Front Plane 30)
PJ2 PCINT26/SEG(Pin Change Interrupt26 or LCD Front Plane 31)
PJ1 PCINT25/SEG(Pin Change Interrupt25 or LCD Front Plane 34)
PJ0 PCINT24/SEG (Pin Change Interrupt26 or LCD Front Plane 35)
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• PCINT28/SEG – Port J, Bit 4
PCINT28, Pin Change Interrupt Source 28: The PE28 pin can serve as an external interrupt
source.
SEG, LCD front plane 29.
• PCINT27/SEG – Port J, Bit 3
PCINT27, Pin Change Interrupt Source 27: The PE27 pin can serve as an external interrupt
source.
SEG, LCD front plane 30.
• PCINT26/SEG – Port J, Bit 2
PCINT26, Pin Change Interrupt Source 26: The PE26 pin can serve as an external interrupt
source.
SEG, LCD front plane 31.
• PCINT25/SEG – Port J, Bit 1
PCINT25, Pin Change Interrupt Source 25: The PE25 pin can serve as an external interrupt
source.
SEG, LCD front plane 34.
• PCINT24/SEG – Port J, Bit 0
PCINT24, Pin Change Interrupt Source 24: The PE24 pin can serve as an external interrupt
source.
SEG, LCD front plane 35.
Table 13-28 and Table 13-29 relates the alternate functions of Port J to the overriding signals
shown in Figure 13-5 on page 65.
Table 13-28. Overriding Signals for Alternate Functions in PJ7:4
Signal
Name
PJ6/PCINT30/
SEG27
PJ5/PCINT29/
SEG28
PJ4/PCINT28/
SEG29
PUOE LCDENLCDENLCDEN
PUOV 0 0 0
DDOE LCDENLCDENLCDEN
DDOV 0 0 0
PVOE 0 0 0
PVOV 0 0 0
PTOE – – –
DIEOE PCINT30 •
PCIE0 •LCDEN •
LCDPM
PCINT29 •
PCIE0 •LCDEN •
LCDPM
PCINT28 •
PCIE0 •LCDEN •
LCDPM
DIEOV
DI
AIO LCDSEG LCDSEG LCDSEG
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Table 13-29. Overriding Signals for Alternate Functions in PH3:0
Signal
Name
PJ3/PCINT27/
SEG30
PJ2/PCINT26/
SEG31
PJ1/PCINT25/
SEG34
PJ0/PCINT24/
SEG35
PUOE LCDENLCDENLCDENLCDEN
PUOV0000
DDOE LCDENLCDENLCDENLCDEN
DDOV 0 0 0 0
PVOE0000
PVOV0000
PTOE––––
DIEOE PCINT27 •
PCIE0 •LCDEN •
LCDPM
PCINT26 •
PCIE0 •LCDEN •
LCDPM
PCINT25 •
PCIE0 •LCDEN •
LCDPM
PCINT24 •
PCIE0 •LCDEN •
LCDPM
DIEOV
DI
AIO LCDSEG LCDSEG LCDSEG LCDSEG
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13.4 Register Description
13.4.1 MCUCR – MCU Control Register
• Bit 4 – PUD: Pull-up Disable
When this bit is written to one, the pull-ups in the I/O ports are disabled even if the DDxn and
PORTxn Registers are configured to enable the pull-ups ({DDxn, PORTxn} = 0b01). See “Con-
figuring the Pin” on page 60 for more details about this feature.
13.4.2 PORTA – Port A Data Register
13.4.3 DDRA – Port A Data Direction Register
13.4.4 PINA – Port A Input Pins Address
13.4.5 PORTB – Port B Data Register
13.4.6 DDRB – Port B Data Direction Register
13.4.7 PINB – Port B Input Pins Address
Bit 7 6 5 4 3 2 1 0
0x35 (0x55) JTD ––PUD– – IVSEL IVCE MCUCR
Read/Write R/W R R R/W R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
0x22 (0x42) 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 Value00000000
Bit 76543210
0x01 (0x21) DDA7 DDA6 DDA5 DDA4 DDA3 DDA2 DDA1 DDA0 DDRA
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x00 (0x20) PINA7 PINA6 PINA5 PINA4 PINA3 PINA2 PINA1 PINA0 PINA
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A
Bit 76543210
0x05 (0x25) PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 PORTB
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x04 (0x24) DDB7 DDB6 DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 DDRB
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x03 (0x23) PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 PINB
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A
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13.4.8 PORTC – Port C Data Register
13.4.9 DDRC – Port C Data Direction Register
13.4.10 PINC – Port C Input Pins Address
13.4.11 PORTD – Port D Data Register
13.4.12 DDRD – Port D Data Direction Register
13.4.13 PIND – Port D Input Pins Address
13.4.14 PORTE – Port E Data Register
13.4.15 DDRE – Port E Data Direction Register
Bit 76543210
0x08 (0x28)PORTC7 PORTC6 PORTC5 PORTC4 PORTC3 PORTC2 PORTC1 PORTC0 PORTC
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x07 (0x27) DDC7 DDC6 DDC5 DDC4 DDC3 DDC2 DDC1 DDC0 DDRC
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x06 (0x26) PINC7 PINC6 PINC5 PINC4 PINC3 PINC2 PINC1 PINC0 PINC
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A
Bit 76543210
0x0B (0x2B) PORTD7 PORTD6 PORTD5 PORTD4 PORTD3 PORTD2 PORTD1 PORTD0 PORTD
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x0A (0x2A) DDD7 DDD6 DDD5 DDD4 DDD3 DDD2 DDD1 DDD0 DDRD
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x09 (0x29) PIND7 PIND6 PIND5 PIND4 PIND3 PIND2 PIND1 PIND0 PIND
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A
Bit 76543210
0x0E (0x2E) PORTE7 PORTE6 PORTE5 PORTE4 PORTE3 PORTE2 PORTE1 PORTE0 PORTE
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x0D (0x2D) DDE7 DDE6 DDE5 DDE4 DDE3 DDE2 DDE1 DDE0 DDRE
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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13.4.16 PINE – Port E Input Pins Address
13.4.17 PORTF – Port F Data Register
13.4.18 DDRF – Port F Data Direction Register
13.4.19 PINF – Port F Input Pins Address
13.4.20 PORTG – Port G Data Register
13.4.21 DDRG – Port G Data Direction Register
13.4.22 PING – Port G Input Pins Address
13.4.23 PORTH – Port H Data Register(1)
Bit 76543210
0x0C (0x2C) PINE7 PINE6 PINE5 PINE4 PINE3 PINE2 PINE1 PINE0 PINE
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A
Bit 76543210
0x11 (0x31) PORTF7 PORTF6 PORTF5 PORTF4 PORTF3 PORTF2 PORTF1 PORTF0 PORTF
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x10 (0x30) DDF7 DDF6 DDF5 DDF4 DDF3 DDF2 DDF1 DDF0 DDRF
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x0F (0x2F) PINF7 PINF6 PINF5 PINF4 PINF3 PINF2 PINF1 PINF0 PINF
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A
Bit 76543210
0x14 (0x34) –––
PORTG4 PORTG3 PORTG2 PORTG1 PORTG0 PORTG
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
Bit 76543210
0x13 (0x33) – – – DDG4 DDG3 DDG2 DDG1 DDG0 DDRG
Read/Write R R R R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x12 (0x32) – – PING5 PING4 PING3 PING2 PING1 PING0 PING
Read/Write R R R R/W R/W R/W R/W R/W
Initial Value 0 0 0 N/A N/A N/A N/A N/A
Bit 7 6543210
(0xDA) PORTH7 PORTH6 PORTH5 PORTH4 PORTH3 PORTH2 PORTH1 PORTH0 PORTH
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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13.4.24 DDRH – Port H Data Direction Register(1)
13.4.25 PINH – Port H Input Pins Address(1)
13.4.26 PORTJ – Port J Data Register(1)
13.4.27 DDRJ – Port J Data Direction Register(1)
13.4.28 PINJ – Port J Input Pins Address(1)
Note: 1. Register only available in ATmega3290/6490.
Bit 76543210
(0xD9) DDH7 DDH6 DDH5 DDH4 DDH3 DDH2 DDH1 DDH0 DDRH
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
(0xD8)PINH7 PINH6 PINH5 PINH4 PINH3 PINH2 PINH1 PINH0 PINH
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A
Bit 76543210
(0xDD) –PORTJ6 PORTJ5 PORTJ4 PORTJ3 PORTJ2 PORTJ1 PORTJ0 PORTJ
Read/Write R R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
(0xDC) – DDJ6 DDJ5 DDJ4 DDJ3 DDJ2 DDJ1 DDJ0 DDRJ
Read/Write R R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
(0xDB) – PINJ6 PINJ5 PINJ4 PINJ3 PINJ2 PINJ1 PINJ0 PINJ
Read/Write R R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 N/A N/A N/A N/A N/A N/A N/A
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14. 8-bit Timer/Counter0 with PWM
14.1 Features
Timer/Counter0 is a general purpose, single compare unit, 8-bit Timer/Counter module. The
main features are:
•Single Compare Unit Counter
•Clear Timer on Compare Match (Auto Reload)
•Glitch-free, Phase Correct Pulse Width Modulator (PWM)
•Frequency Generator
•External Event Counter
•10-bit Clock Prescaler
•Overflow and Compare Match Interrupt Sources (TOV0 and OCF0A)
14.2 Overview
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 14-1. For the actual
placement of I/O pins, refer to “Pinout ATmega3290/6490” on page 2 and “Pinout
ATmega329/649” on page 3. 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 “Register
Description” on page 103.
Figure 14-1. 8-bit Timer/Counter Block Diagram
14.2.1 Registers
The Timer/Counter (TCNT0) and Output Compare Register (OCR0A) are 8-bit registers. Inter-
rupt 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 Reg-
ister (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
Timer/Counter
DATA BU S
=
TCNTn
Waveform
Generation OCn
= 0
Control Logic
=
0xFF
BOTTOM
count
clear
direction
TOVn
(Int.Req.)
OCRn
TCCRn
Clock Select
Tn
Edge
Detector
( From Prescaler )
clk
Tn
TOP
OCn
(Int.Req.)
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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 Register (OCR0A) is compared with the Timer/Counter
value at all times. The result of the compare can be used by the Waveform Generator to gener-
ate a PWM or variable frequency output on the Output Compare pin (OC0A). See “Output
Compare Unit” on page 93. for details. The compare match event will also set the Compare Flag
(OCF0A) which can be used to generate an Output Compare interrupt request.
14.2.2 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 Com-
pare unit number, in this case unit A. 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 14-1 are also used extensively throughout the document.
14.3 Timer/Counter Clock Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock source
is selected by the Clock Select logic which is controlled by the Clock Select (CS02:0) bits
located in the Timer/Counter Control Register (TCCR0A). For details on clock sources and pres-
caler, see “Timer/Counter0 and Timer/Counter1 Prescalers” on page 107.
Table 14-1. Definitions of Timer/Counter values.
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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14.4 Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure
14-2 shows a block diagram of the counter and its surroundings.
Figure 14-2. 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). 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
“Modes of Operation” on page 97.
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.
14.5 Output Compare Unit
The 8-bit comparator continuously compares TCNT0 with the Output Compare Register
(OCR0A). Whenever TCNT0 equals OCR0A, the comparator signals a match. A match will set
the Output Compare Flag (OCF0A) at the next timer clock cycle. If enabled (OCIE0A = 1 and
Global Interrupt Flag in SREG is set), the Output Compare Flag generates an Output Compare
interrupt. The OCF0A Flag is automatically cleared when the interrupt is executed. Alternatively,
the OCF0A Flag can be cleared by software by writing a logical one to its I/O bit location. The
DATA B U S
TCNTn Control Logic
count
TOVn
(Int.Req.)
Clock Select
top
Tn
Edge
Detector
( From Prescaler )
clk
Tn
bottom
direction
clear
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Waveform Generator uses the match signal to generate an output according to operating mode
set by the WGM01:0 bits and Compare Output mode (COM0A1:0) bits. The max and bottom sig-
nals are used by the Waveform Generator for handling the special cases of the extreme values
in some modes of operation (See “Modes of Operation” on page 97.).
Figure 14-3 shows a block diagram of the Output Compare unit.
Figure 14-3. Output Compare Unit, Block Diagram
OCFnx (Int.Req.)
= (8-bit Comparator )
OCRnx
OCnx
DATA BU S
TCNTn
WGMn1:0
Waveform Generator
top
FOCn
COMnX1:0
bottom
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The OCR0A Register is double buffered when using any of the Pulse Width Modulation (PWM)
modes. For the normal and Clear Timer on Compare (CTC) modes of operation, the double buff-
ering is disabled. The double buffering synchronizes the update of the OCR0 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 OCR0A Register access may seem complex, but this is not case. When the double buffer-
ing is enabled, the CPU has access to the OCR0A Buffer Register, and if double buffering is
disabled the CPU will access the OCR0A directly.
14.5.1 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 (FOC0A) bit. Forcing compare match will not set the
OCF0A Flag or reload/clear the timer, but the OC0A pin will be updated as if a real compare
match had occurred (the COM0A1:0 bits settings define whether the OC0A pin is set, cleared or
toggled).
14.5.2 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 OCR0A to be initial-
ized to the same value as TCNT0 without triggering an interrupt when the Timer/Counter clock is
enabled.
14.5.3 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 OCR0A 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
counting down.
The setup of the OC0A should be performed before setting the Data Direction Register for the
port pin to output. The easiest way of setting the OC0A value is to use the Force Output Com-
pare (FOC0A) strobe bits in Normal mode. The OC0A Register keeps its value even when
changing between Waveform Generation modes.
Be aware that the COM0A1:0 bits are not double buffered together with the compare value.
Changing the COM0A1:0 bits will take effect immediately.
14.6 Compare Match Output Unit
The Compare Output mode (COM0A1:0) bits have two functions. The Waveform Generator
uses the COM0A1:0 bits for defining the Output Compare (OC0A) state at the next compare
match. Also, the COM0A1:0 bits control the OC0A pin output source. Figure 14-4 shows a sim-
plified schematic of the logic affected by the COM0A1:0 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 regis-
ters (DDR and PORT) that are affected by the COM0A1:0 bits are shown. When referring to the
OC0A state, the reference is for the internal OC0A Register, not the OC0A pin. If a System
Reset occur, the OC0A Register is reset to “0”.
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Figure 14-4. Compare Match Output Unit, Schematic
The general I/O port function is overridden by the Output Compare (OC0A) from the Waveform
Generator if either of the COM0A1:0 bits are set. However, the OC0A pin direction (input or out-
put) is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction
Register bit for the OC0A pin (DDR_OC0A) must be set as output before the OC0A value is vis-
ible 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 OC0A state before the
output is enabled. Note that some COM0A1:0 bit settings are reserved for certain modes of
operation. See “Register Description” on page 103.
14.6.1 Compare Output Mode and Waveform Generation
The Waveform Generator uses the COM0A1:0 bits differently in Normal, CTC, and PWM
modes. For all modes, setting the COM0A1:0 = 0 tells the Waveform Generator that no action on
the OC0A Register is to be performed on the next compare match. For compare output actions
in the non-PWM modes refer to Table 14-3 on page 104. For fast PWM mode, refer to Table 14-
4 on page 104, and for phase correct PWM refer to Table 14-5 on page 105.
A change of the COM0A1:0 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
FOC0A strobe bits.
PORT
DDR
DQ
DQ
OCn
Pin
OCnx
DQ
Waveform
Generator
COMnx1
COMnx0
0
1
DATA BU S
FOCn
clk
I/O
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14.7 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 (WGM01:0) and Compare Output
mode (COM0A1:0) bits. The Compare Output mode bits do not affect the counting sequence,
while the Waveform Generation mode bits do. The COM0A1:0 bits control whether the PWM
output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM
modes the COM0A1:0 bits control whether the output should be set, cleared, or toggled at a
compare match (See “Compare Match Output Unit” on page 95.).
For detailed timing information refer to Figure 14-8, Figure 14-9, Figure 14-10 and Figure 14-11
in “Timer/Counter Timing Diagrams” on page 101.
14.7.1 Normal Mode
The simplest mode of operation is the Normal mode (WGM01:0 = 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 bot-
tom (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 Out-
put Compare to generate waveforms in Normal mode is not recommended, since this will
occupy too much of the CPU time.
14.7.2 Clear Timer on Compare Match (CTC) Mode
In Clear Timer on Compare or CTC mode (WGM01:0 = 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 14-5. The counter value (TCNT0)
increases until a compare match occurs between TCNT0 and OCR0A, and then counter
(TCNT0) is cleared.
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Figure 14-5. CTC Mode, Timing Diagram
An interrupt can be generated each time the counter value reaches the TOP value by using the
OCF0A Flag. If the interrupt is enabled, the interrupt handler routine can be used for updating
the TOP value. However, changing TOP to a value close to BOTTOM when the counter is run-
ning with none or a low prescaler value must be done with care since the CTC mode does not
have the double buffering feature. If the new value written to OCR0A is lower than the current
value of TCNT0, the counter will miss the compare match. The counter will then have to count to
its maximum value (0xFF) and wrap around starting at 0x00 before the compare match can
occur.
For generating a waveform output in CTC mode, the OC0A output can be set to toggle its logical
level on each compare match by setting the Compare Output mode bits to toggle mode
(COM0A1:0 = 1). The OC0A value will not be visible on the port pin unless the data direction for
the pin is set to output. The waveform generated will have a maximum frequency of fOC0 =
fclk_I/O/2 when OCR0A is set to zero (0x00). The waveform frequency is defined by the following
equation:
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
As for the Normal mode of operation, the TOV0 Flag is set in the same timer clock cycle that the
counter counts from MAX to 0x00.
14.7.3 Fast PWM Mode
The fast Pulse Width Modulation or fast PWM mode (WGM01:0 = 3) provides a high frequency
PWM waveform generation option. The fast PWM differs from the other PWM option by its sin-
gle-slope operation. The counter counts from BOTTOM to MAX then restarts from BOTTOM. In
non-inverting Compare Output mode, the Output Compare (OC0A) is cleared on the compare
match between TCNT0 and OCR0A, 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 MAX value.
The counter is then cleared at the following timer clock cycle. The timing diagram for the fast
PWM mode is shown in Figure 14-6. The TCNT0 value is in the timing diagram shown as a his-
TCNTn
OCn
(Toggle)
OCnx Interrupt Flag Set
1 4
Period
2 3
(COMnx1:0 = 1)
fOCnx
fclk_I/O
2N1OCRnx+()⋅⋅
--------------------------------------------------=
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togram 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 OCR0A and TCNT0.
Figure 14-6. Fast PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches MAX. If the inter-
rupt 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 OC0A pin.
Setting the COM0A1:0 bits to two will produce a non-inverted PWM and an inverted PWM output
can be generated by setting the COM0A1:0 to three (See Table 14-4 on page 104). The actual
OC0A value will only be visible on the port pin if the data direction for the port pin is set as out-
put. The PWM waveform is generated by setting (or clearing) the OC0A Register at the compare
match between OCR0A and TCNT0, and clearing (or setting) the OC0A Register at the timer
clock cycle the counter is cleared (changes from MAX 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 set-
ting OC0A to toggle its logical level on each compare match (COM0A1:0 = 1). The waveform
generated will have a maximum frequency of fOC0 = fclk_I/O/2 when OCR0A is set to zero. This
feature is similar to the OC0A toggle in CTC mode, except the double buffer feature of the Out-
put Compare unit is enabled in the fast PWM mode.
TCNTn
OCRnx Update and
TOVn Interrupt Flag Set
1
Period
2 3
OCn
OCn
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCRnx Interrupt Flag Set
4 5 6 7
fOCnxPWM
fclk_I/O
N256⋅
------------------=
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14.7.4 Phase Correct PWM Mode
The phase correct PWM mode (WGM01:0 = 1) 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 MAX and then from MAX to BOTTOM. In non-
inverting Compare Output mode, the Output Compare (OC0A) is cleared on the compare match
between TCNT0 and OCR0A while counting up, and set on the compare match while counting
down. 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 sym-
metric feature of the dual-slope PWM modes, these modes are preferred for motor control
applications.
The PWM resolution for the phase correct PWM mode is fixed to eight bits. In phase correct
PWM mode the counter is incremented until the counter value matches MAX. When the counter
reaches MAX, it changes the count direction. The TCNT0 value will be equal to MAX for one
timer clock cycle. The timing diagram for the phase correct PWM mode is shown on Figure 14-7.
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 OCR0A and TCNT0.
Figure 14-7. 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
OC0A pin. Setting the COM0A1:0 bits to two will produce a non-inverted PWM. An inverted
PWM output can be generated by setting the COM0A1:0 to three (See Table 14-5 on page 105).
The actual OC0A 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 OC0A Register at the
compare match between OCR0A and TCNT0 when the counter increments, and setting (or
clearing) the OC0A Register at compare match between OCR0A and TCNT0 when the counter
TOVn Interrupt Flag Set
OCnx Interrupt Flag Set
1 2 3
TCNTn
Period
OCn
OCn
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCRnx Update
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decrements. The PWM frequency for the output when using phase correct PWM can be calcu-
lated 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 14-7 OCn has a transition from high to low even though
there is no Compare Match. The point of this transition is to guarantee symmetry around BOT-
TOM. There are two cases that give a transition without Compare Match.
• OCR0A changes its value from MAX, like in Figure 14-7. 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.
14.8 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 14-8 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 14-8. Timer/Counter Timing Diagram, no Prescaling
Figure 14-9 shows the same timing data, but with the prescaler enabled.
fOCnxPCPWM
fclk_I/O
N510⋅
------------------=
clk
Tn
(clk
I/O
/1)
TOVn
clk
I/O
TCNTn MAX - 1 MAX BOTTOM BOTTOM + 1
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Figure 14-9. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
Figure 14-10 shows the setting of OCF0A in all modes except CTC mode.
Figure 14-10. Timer/Counter Timing Diagram, Setting of OCF0A, with Prescaler (fclk_I/O/8)
TOVn
TCNTn MAX - 1 MAX BOTTOM BOTTOM + 1
clk
I/O
clk
Tn
(clk
I/O
/8)
OCFnx
OCRnx
TCNTn
OCRnx Value
OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2
clkI/O
clkTn
(clkI/O/8)
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Figure 14-11 shows the setting of OCF0A and the clearing of TCNT0 in CTC mode.
Figure 14-11. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with Pres-
caler (fclk_I/O/8)
14.9 Register Description
14.9.1 TCCR0A – Timer/Counter Control Register A
• Bit 7 – FOC0A: Force Output Compare A
The FOC0A bit is only active when the WGM00 bit specifies a non-PWM mode. However, for
ensuring compatibility with future devices, this bit must be set to zero when TCCR0 is written
when operating in PWM mode. When writing a logical one to the FOC0A bit, an immediate com-
pare 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, 3 – WGM01:0: Waveform Generation Mode
These bits control the counting sequence of the counter, the source for the maximum (TOP)
counter value, and what type of waveform generation to be used. Modes of operation supported
by the Timer/Counter unit are: Normal mode, Clear Timer on Compare match (CTC) mode, and
two types of Pulse Width Modulation (PWM) modes. See Table 14-2 and “Modes of Operation”
on page 97.
OCFnx
OCRnx
TCNTn
(CTC)
TOP
TOP - 1 TOP BOTTOM BOTTOM + 1
clkI/O
clkTn
(clkI/O/8)
Bit 7 6 5 4 3 2 1 0
0x24 (0x44) FOC0A WGM00 COM0A1 COM0A0 WGM01 CS02 CS01 CS00 TCCR0A
Read/Write 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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Note: 1. The CTC0 and PWM0 bit definition names are now obsolete. Use the WGM01:0 definitions.
However, the functionality and location of these bits are compatible with previous versions of
the timer.
• Bit 5:4 – COM0A1:0: Compare Match Output 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
WGM01:0 bit setting. Table 14-3 shows the COM0A1:0 bit functionality when the WGM01:0 bits
are set to a normal or CTC mode (non-PWM).
Table 14-4 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to fast PWM
mode.
Note: 1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the com-
pare match is ignored, but the set or clear is done at BOTTOM. See “Fast PWM Mode” on
page 98 for more details.
Table 14-5 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to phase cor-
rect PWM mode.
Table 14-2. Waveform Generation Mode Bit Description(1)
Mode
WGM01
(CTC0)
WGM00
(PWM0)
Timer/Counter
Mode of Operation TOP
Update of
OCR0A at
TOV0 Flag
Set on
00 0Normal 0xFF Immediate MAX
1 0 1 PWM, Phase Correct 0xFF TOP BOTTOM
2 1 0 CTC OCR0A Immediate MAX
31 1Fast PWM 0xFFBOTTOMMAX
Table 14-3. Compare Output Mode, non-PWM Mode
COM0A1 COM0A0 Description
00Normal port operation, OC0A disconnected.
0 1 Toggle OC0A on compare match
1 0 Clear OC0A on compare match
1 1 Set OC0A on compare match
Table 14-4. Compare Output Mode, Fast PWM Mode(1)
COM0A1 COM0A0 Description
00Normal port operation, OC0A disconnected.
01Reserved
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)
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Note: 1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the com-
pare match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on
page 100 for more details.
• Bit 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.
14.9.2 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 OCR0A Register.
14.9.3 OCR0A – Output Compare Register A
Table 14-5. Compare Output Mode, Phase Correct PWM Mode(1)
COM0A1 COM0A0 Description
00Normal port operation, OC0A disconnected.
01Reserved
1 0 Clear OC0A on compare match when up-counting. Set OC0A on
compare match when counting down.
1 1 Set OC0A on compare match when up-counting. Clear OC0A on
compare match when counting down.
Table 14-6. Clock Select Bit Description
CS02 CS01 CS00 Description
000No clock source (Timer/Counter stopped)
001clk
I/O/(No prescaling)
010clk
I/O/8 (From prescaler)
011clk
I/O/64 (From prescaler)
100clk
I/O/256 (From prescaler)
101clk
I/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.
Bit 76543210
0x26 (0x46) 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
0x27 (0x47) OCR0A[7:0] OCR0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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The Output Compare 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.
14.9.4 TIMSK0 – Timer/Counter 0 Interrupt Mask Register
• 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 (one), 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/Coun-
ter 0 Interrupt Flag Register – TIFR0.
• Bit 0 – TOIE0: Timer/Counter0 Overflow Interrupt Enable
When the TOIE0 bit is written to one, and the I-bit in the Status Register is set (one), 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 Inter-
rupt Flag Register – TIFR0.
14.9.5 TIFR0 – Timer/Counter 0 Interrupt Flag Register
• Bit 1 – OCF0A: Output Compare Flag 0 A
The OCF0A bit is set (one) 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 (one), the Timer/Counter0 Compare match Interrupt is executed.
• Bit 0 – TOV0: Timer/Counter0 Overflow Flag
The bit TOV0 is set (one) when an overflow occurs in Timer/Counter0. TOV0 is cleared by hard-
ware 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 Inter-
rupt Enable), and TOV0 are set (one), the Timer/Counter0 Overflow interrupt is executed. In
phase correct PWM mode, this bit is set when Timer/Counter0 changes counting direction at
0x00.
Bit 76543210
(0x6E) ––––––OCIE0ATOIE0TIMSK0
Read/WriteRRRRRRR/WR/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
0x15 (0x35) ––––––OCF0ATOV0 TIFR0
Read/WriteRRRRRRR/WR/W
Initial Value00000000
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15. Timer/Counter0 and Timer/Counter1 Prescalers
Timer/Counter1 and Timer/Counter0 share the same prescaler module, but the Timer/Counters
can have different prescaler settings. The description below applies to both Timer/Counter1 and
Timer/Counter0.
15.0.1 Internal Clock Source
The Timer/Counter can be clocked directly by the system clock (by setting the CSn2:0 = 1). This
provides the fastest operation, with a maximum Timer/Counter clock frequency equal to system
clock frequency (fCLK_I/O). Alternatively, one of four taps from the prescaler can be used as a
clock source. The prescaled clock has a frequency of either fCLK_I/O/8, fCLK_I/O/64, fCLK_I/O/256, or
fCLK_I/O/1024.
15.0.2 Prescaler Reset
The prescaler is free running, i.e., operates independently of the Clock Select logic of the
Timer/Counter, and it is shared by Timer/Counter1 and Timer/Counter0. Since the prescaler is
not affected by the Timer/Counter’s clock select, the state of the prescaler will have implications
for situations where a prescaled clock is used. One example of prescaling artifacts occurs when
the timer is enabled and clocked by the prescaler (6 > CSn2:0 > 1). The number of system clock
cycles from when the timer is enabled to the first count occurs can be from 1 to N+1 system
clock cycles, where N equals the prescaler divisor (8, 64, 256, or 1024).
It is possible to use the prescaler reset for synchronizing the Timer/Counter to program execu-
tion. However, care must be taken if the other Timer/Counter that shares the same prescaler
also uses prescaling. A prescaler reset will affect the prescaler period for all Timer/Counters it is
connected to.
15.0.3 External Clock Source
An external clock source applied to the T1/T0 pin can be used as Timer/Counter clock
(clkT1/clkT0). The T1/T0 pin is sampled once every system clock cycle by the pin synchronization
logic. The synchronized (sampled) signal is then passed through the edge detector. Figure 15-1
shows a functional equivalent block diagram of the T1/T0 synchronization and edge detector
logic. The registers are clocked at the positive edge of the internal system clock (clkI/O). The latch
is transparent in the high period of the internal system clock.
The edge detector generates one clkT1/clkT0 pulse for each positive (CSn2:0 = 7) or negative
(CSn2:0 = 6) edge it detects.
Figure 15-1. T1/T0 Pin Sampling
The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system clock cycles
from an edge has been applied to the T1/T0 pin to the counter is updated.
Tn_sync
(To Clock
Select Logic)
Edge DetectorSynchronization
DQDQ
LE
DQ
Tn
clkI/O
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Enabling and disabling of the clock input must be done when T1/T0 has been stable for at least
one system clock cycle, otherwise it is a risk that a false Timer/Counter clock pulse is generated.
Each half period of the external clock applied must be longer than one system clock cycle to
ensure correct sampling. The external clock must be guaranteed to have less than half the sys-
tem 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 fre-
quency (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 15-2. Prescaler for Timer/Counter0 and Timer/Counter1(1)
Note: 1. The synchronization logic on the input pins (T1/T0) is shown in Figure 15-1.
15.1 Register Description
15.1.1 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 PSR2 and PSR10 bits is kept, hence keeping the corresponding pres-
caler reset signals asserted. This ensures that the corresponding Timer/Counters are halted and
can be configured to the same value without the risk of one of them advancing during configura-
tion. When the TSM bit is written to zero, the PSR2 and PSR10 bits are cleared by hardware,
and the Timer/Counters start counting simultaneously.
• Bit 0 – PSR10: Prescaler Reset Timer/Counter1 and Timer/Counter0
PSR10
Clear
clk
T1
clk
T0
T1
T0
clk
I/O
Synchronization
Synchronization
Bit 7 6 5 4 3 2 1 0
0x23 (0x43) TSM – – – – – PSR2 PSR10 GTCCR
Read/Write R/W R R R R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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When this bit is one, Timer/Counter1 and Timer/Counter0 prescaler will be Reset. This bit is nor-
mally cleared immediately by hardware, except if the TSM bit is set. Note that Timer/Counter1
and Timer/Counter0 share the same prescaler and a reset of this prescaler will affect both
timers.
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16. 16-bit Timer/Counter1
16.1 Features
The 16-bit Timer/Counter unit allows accurate program execution timing (event management),
wave generation, and signal timing measurement. The main features are:
•True 16-bit Design (i.e., Allows 16-bit PWM)
•Two independent Output Compare Units
•Double Buffered Output Compare Registers
•One Input Capture Unit
•Input Capture Noise Canceler
•Clear Timer on Compare Match (Auto Reload)
•Glitch-free, Phase Correct Pulse Width Modulator (PWM)
•Variable PWM Period
•Frequency Generator
•External Event Counter
•Four independent interrupt Sources (TOV1, OCF1A, OCF1B, and ICF1)
16.2 Overview
Most register and bit references in this section are written in general form. A lower case “n”
replaces the Timer/Counter number, and a lower case “x” replaces the Output Compare unit.
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 16-1. For the actual
placement of I/O pins, refer to “Pinout ATmega3290/6490” on page 2. CPU accessible I/O Reg-
isters, 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 “Register Description” on page 132.
The PRTIM1 bit in “Power Reduction Register” on page 37 must be written to zero to enable the
Timer/Counter1 module.
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Figure 16-1. 16-bit Timer/Counter Block Diagram(1)
Note: 1. Refer to Figure 1-1 on page 2, Table 13-5 on page 68, and Table 13-11 on page 72 for
Timer/Counter1 pin placement and description.
16.2.1 Registers
The Timer/Counter (TCNT1), Output Compare Registers (OCR1A/B), and Input Capture Regis-
ter (ICR1) are all 16-bit registers. Special procedures must be followed when accessing the 16-
bit registers. These procedures are described in the section “Accessing 16-bit Registers” on
page 113. The Timer/Counter Control Registers (TCCR1A/B) are 8-bit registers and have no
CPU access restrictions. Interrupt requests (abbreviated to Int.Req. in the figure) signals are all
visible in the Timer Interrupt Flag Register (TIFR1). All interrupts are individually masked with
the Timer Interrupt Mask Register (TIMSK1). TIFR1 and TIMSK1 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on
the T1 pin. The Clock Select logic block controls which clock source and edge the Timer/Counter
uses to increment (or decrement) its value. The Timer/Counter is inactive when no clock source
is selected. The output from the Clock Select logic is referred to as the timer clock (clkT1).
The double buffered Output Compare Registers (OCR1A/B) are compared with the Timer/Coun-
ter 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 “Out-
Clock Select
Timer/Counter
DATA B U S
OCRnA
OCRnB
ICRn
=
=
TCNTn
Waveform
Generation
Waveform
Generation
OCnA
OCnB
Noise
Canceler
ICPn
=
Fixed
TOP
Values
Edge
Detector
Control Logic
=
0
TOP BOTTOM
Count
Clear
Direction
TOVn
(Int.Req.)
OCnA
(Int.Req.)
OCnB
(Int.Req.)
ICFn (Int.Req.)
TCCRnA TCCRnB
( From Analog
Comparator Ouput )
Tn
Edge
Detector
( From Prescaler )
clk
Tn
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put Compare Units” on page 119.. 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 trig-
gered) event on either the Input Capture pin (ICP1) or on the Analog Comparator pins (See
“Analog Comparator” on page 207.) The Input Capture unit includes a digital filtering unit (Noise
Canceler) for reducing the chance of capturing noise spikes.
The TOP value, or maximum Timer/Counter value, can in some modes of operation be defined
by either the OCR1A Register, the ICR1 Register, or by a set of fixed values. When using
OCR1A as TOP value in a PWM mode, the OCR1A Register can not be used for generating a
PWM output. However, the TOP value will in this case be double buffered allowing the TOP
value to be changed in run time. If a fixed TOP value is required, the ICR1 Register can be used
as an alternative, freeing the OCR1A to be used as PWM output.
16.2.2 Definitions
The following definitions are used extensively throughout the section:
16.2.3 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:
• FOC1A and FOC1B are added to TCCR1C.
• WGM13 is added to TCCR1B.
The 16-bit Timer/Counter has improvements that will affect the compatibility in some special
cases.
Table 16-1. Definitions of Timer/Counter values.
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 Regis-
ter. The assignment is dependent of the mode of operation.
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16.3 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 tempo-
rary 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.
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 “About Code Examples” on page 9.
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 Regis-
ters, then the result of the access outside the interrupt will be corrupted. Therefore, when both
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 main code and the interrupt code update the temporary register, the main code must disable
the interrupts during the 16-bit access.
The following code examples show how to do an atomic read of the TCNT1 Register contents.
Reading any of the OCR1A/B or ICR1 Registers can be done by using the same principle.
Note: 1. See “About Code Examples” on page 9.
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 */
__disable_interrupt();
/* 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 “About Code Examples” on page 9.
The assembly code example requires that the r17:r16 register pair contains the value to be writ-
ten to TCNT1.
16.3.1 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.
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 */
__disable_interrupt();
/* Set TCNT1 to i */
TCNT1 = i;
/* Restore global interrupt flag */
SREG = sreg;
}
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16.4 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 “Timer/Counter0 and Timer/Counter1 Prescalers” on page 107.
16.5 Counter Unit
The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional counter unit.
Figure 16-2 shows a block diagram of the counter and its surroundings.
Figure 16-2. 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).
clkT1Timer/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) con-
taining 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
TEMP (8-bit)
DATA BUS
(8-bit)
TCNTn (16-bit Counter)
TCNTnH (8-bit) TCNTnL (8-bit) Control Logic
Count
Clear
Direction
TOVn
(Int.Req.)
Clock Select
TOP BOTTOM
Tn
Edge
Detector
( From Prescaler )
clkTn
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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 “Modes of Operation” on page 123.
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.
16.6 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 mul-
tiple 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 sig-
nal 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 16-3. 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 16-3. 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
ICFn (Int.Req.)
Analog
Comparator
WRITE ICRn (16-bit Register)
ICRnH (8-bit)
Noise
Canceler
ICPn
Edge
Detector
TEMP (8-bit)
DATA BUS
(8-bit)
ICRnL (8-bit)
TCNTn (16-bit Counter)
TCNTnH (8-bit) TCNTnL (8-bit)
ACIC* ICNC ICES
ACO*
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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 Genera-
tion 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 “Accessing 16-bit Registers”
on page 113.
16.6.1 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 15-1 on page 107). 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 Wave-
form Generation mode that uses ICR1 to define TOP.
An Input Capture can be triggered by software by controlling the port of the ICP1 pin.
16.6.2 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 addi-
tional 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.
16.6.3 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 inter-
rupt handler routine as possible. Even though the Input Capture interrupt has relatively high
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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).
16.7 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 Com-
pare 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 writ-
ing a logical one to its I/O bit location. The Waveform Generator uses the match signal to
generate an output according to operating mode set by the Waveform Generation mode
(WGM13:0) bits and Compare Output mode (COM1x1:0) bits. The TOP and BOTTOM signals
are used by the Waveform Generator for handling the special cases of the extreme values in
some modes of operation (See “Modes of Operation” on page 123.)
A special feature of Output Compare unit A allows it to define the Timer/Counter TOP value (i.e.,
counter resolution). In addition to the counter resolution, the TOP value defines the period time
for waveforms generated by the Waveform Generator.
Figure 16-4 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.
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Figure 16-4. 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 Com-
pare 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 out-
put 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 dis-
abled 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 Reg-
ister 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 “Accessing 16-bit Registers”
on page 113.
16.7.1 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 (FOC1x) bit. Forcing compare match will not set the
OCF1x Flag or reload/clear the timer, but the OC1x pin will be updated as if a real compare
match had occurred (the COM11:0 bits settings define whether the OC1x pin is set, cleared or
toggled).
OCFnx (Int.Req.)
=
(16-bit Comparator )
OCRnx Buffer (16-bit Register)
OCRnxH Buf. (8-bit)
OCnx
TEMP (8-bit)
DATA BUS
(8-bit)
OCRnxL Buf. (8-bit)
TCNTn (16-bit Counter)
TCNTnH (8-bit) TCNTnL (8-bit)
COMnx1:0WGMn3:0
OCRnx (16-bit Register)
OCRnxH (8-bit) OCRnxL (8-bit)
Waveform Generator
TOP
BOTTOM
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16.7.2 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.
16.7.3 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
units, 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 counting down.
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 Com-
pare (FOC1x) strobe bits in Normal mode. The OC1x Register keeps its value even when
changing between Waveform Generation modes.
Be aware that the COM1x1:0 bits are not double buffered together with the compare value.
Changing the COM1x1:0 bits will take effect immediately.
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16.8 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 16-5 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 16-5. 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 out-
put) 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 visi-
ble on the pin. The port override function is generally independent of the Waveform Generation
mode, but there are some exceptions. Refer to Table 16-2, Table 16-3 and Table 16-4 for
details.
The design of the Output Compare pin logic allows initialization of the OC1x state before the out-
put is enabled. Note that some COM1x1:0 bit settings are reserved for certain modes of
operation. See “Register Description” on page 132.
The COM1x1:0 bits have no effect on the Input Capture unit.
PORT
DDR
DQ
DQ
OCnx
Pin
OCnx
DQ
Waveform
Generator
COMnx1
COMnx0
0
1
DATA BU S
FOCnx
clk
I/O
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16.8.1 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 16-2 on page 132. For fast PWM mode refer to Table 16-3 on
page 133, and for phase correct and phase and frequency correct PWM refer to Table 16-4 on
page 133.
A change of the COM1x1:0 bits state will have effect at the first compare match after the bits are
written. For non-PWM modes, the action can be forced to have immediate effect by using the
FOC1x strobe bits.
16.9 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 out-
put generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes
the COM1x1:0 bits control whether the output should be set, cleared or toggle at a compare
match (See “Compare Match Output Unit” on page 122.)
For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 130.
16.9.1 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 soft-
ware. 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.
16.9.2 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
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mode allows greater control of the compare match output frequency. It also simplifies the opera-
tion of counting external events.
The timing diagram for the CTC mode is shown in Figure 16-6. The counter value (TCNT1)
increases until a compare match occurs with either OCR1A or ICR1, and then counter (TCNT1)
is cleared.
Figure 16-6. 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. How-
ever, 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 buff-
ering 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 max-
imum 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 fre-
quency of fOC1A = fclk_I/O/2 when OCR1A is set to zero (0x0000). The waveform frequency is
defined by the following equation:
The N variable represents the prescaler factor (1, 8, 64, 256, or 1024).
As for the Normal mode of operation, the TOV1 Flag is set in the same timer clock cycle that the
counter counts from MAX to 0x0000.
16.9.3 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
TCNTn
OCnA
(Toggle)
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
1 4
Period
2 3
(COMnA1:0 = 1)
fOCnA
fclk_I/O
2N1OCRnA+()⋅⋅
---------------------------------------------------=
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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 cor-
rect 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, capaci-
tors), 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 max-
imum 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 16-7. 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 16-7. 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 han-
dler 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
-----------------------------------=
TCNTn
OCRnx / TOP Update
and TOVn Interrupt Flag
Set and OCnA Interrupt
Flag Set or ICFn
Interrupt Flag Set
(Interrupt on TOP)
1 7
Period
2 3 4 5 6 8
OCnx
OCnx
(COMnx1:0 = 2)
(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 16-3 on page 133). The actual
OC1x value will only be visible on the port pin if the data direction for the port pin is set as output
(DDR_OC1x). The PWM waveform is generated by setting (or clearing) the OC1x Register at
the compare match between OCR1x and TCNT1, 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 out-
put 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 set-
ting OC1A to toggle its logical level on each compare match (COM1A1:0 = 1). This applies only
if OCR1A is used to define the TOP value (WGM13:0 = 15). The waveform generated will have
a maximum frequency of fOC1A = fclk_I/O/2 when OCR1A is set to zero (0x0000). This feature is
similar to the OC1A toggle in CTC mode, except the double buffer feature of the Output Com-
pare unit is enabled in the fast PWM mode.
16.9.4 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 counting up, and set on the
compare match while counting down. In inverting Output Compare mode, the operation is
fOCnxPWM
fclk_I/O
N1TOP+()⋅
-----------------------------------=
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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 resolu-
tion in bits can be calculated by using the following equation:
In phase correct PWM mode the counter is incremented until the counter value matches either
one of the fixed values 0x00FF, 0x01FF, or 0x03FF (WGM13:0 = 1, 2, or 3), the value in ICR1
(WGM13:0 = 10), or the value in OCR1A (WGM13:0 = 11). The counter has then reached the
TOP and changes the count direction. The TCNT1 value will be equal to TOP for one timer clock
cycle. The timing diagram for the phase correct PWM mode is shown on Figure 16-8. 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 Inter-
rupt Flag will be set when a compare match occurs.
Figure 16-8. 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 accord-
ingly at the same timer clock cycle as the OCR1x Registers are updated with the double buffer
value (at TOP). The Interrupt Flags can be used to generate an interrupt each time the counter
reaches the TOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the Compare Registers. If the TOP value is lower than any of the
Compare Registers, a compare match will never occur between the TCNT1 and the OCR1x.
RPCPWM
TOP 1+()log
2()log
-----------------------------------=
OCRnx/TOP Update and
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
1 2 3 4
TOVn Interrupt Flag Set
(Interrupt on Bottom)
TCNTn
Period
OCnx
OCnx
(COMnx1:0 = 2)
(COMnx1:0 = 3)
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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 16-8 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 Reg-
ister. 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 1 on page 133).
The actual OC1x value will only be visible on the port pin if the data direction for the port pin is
set as output (DDR_OC1x). The PWM waveform is generated by setting (or clearing) the OC1x
Register at the compare match between OCR1x and TCNT1 when the counter increments, and
clearing (or setting) the OC1x Register at compare match between OCR1x and TCNT1 when
the counter decrements. The PWM frequency for the output when using phase correct PWM can
be calculated by the following equation:
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCR1x Register represent special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCR1x is set equal to BOTTOM the
output will be continuously low and if set equal to TOP the output will be continuously high for
non-inverted PWM mode. For inverted PWM the output will have the opposite logic values. If
OCR1A is used to define the TOP value (WGM13:0 = 11) and COM1A1:0 = 1, the OC1A output
will toggle with a 50% duty cycle.
16.9.5 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 wave-
form 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
counting up, and set on the compare match while counting down. In inverting Compare Output
mode, the operation is inverted. The dual-slope operation gives a lower maximum operation fre-
quency 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 16-
8 and Figure 16-9).
fOCnxPCPWM
fclk_I/O
2NTOP⋅⋅
----------------------------=
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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:
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 16-9. 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 dia-
gram 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 repre-
sent compare matches between OCR1x and TCNT1. The OC1x Interrupt Flag will be set when a
compare match occurs.
Figure 16-9. 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 16-9 shows the output generated is, in contrast to the phase correct mode, symmetri-
cal 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.
RPFCPWM
TOP 1+()log
2()log
-----------------------------------=
OCRnx/TOP Updateand
TOVn Interrupt Flag Set
(Interrupt on Bottom)
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
1 2 3 4
TCNTn
Period
OCnx
OCnx
(COMnx1:0 = 2)
(COMnx1:0 = 3)
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Using the ICR1 Register for defining TOP works well when using fixed TOP values. By using
ICR1, the OCR1A Register is free to be used for generating a PWM output on OC1A. However,
if the base PWM frequency is actively changed by changing the TOP value, using the OCR1A as
TOP is clearly a better choice due to its double buffer feature.
In phase and frequency correct PWM mode, the compare units allow generation of PWM wave-
forms 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 1 on
page 133). The actual OC1x value will only be visible on the port pin if the data direction for the
port pin is set as output (DDR_OC1x). The PWM waveform is generated by setting (or clearing)
the OC1x Register at the compare match between OCR1x and TCNT1 when the counter incre-
ments, 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. If OCR1A
is used to define the TOP value (WGM13:0 = 9) and COM1A1:0 = 1, the OC1A output will toggle
with a 50% duty cycle.
16.10 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 16-10 shows a timing diagram for the setting of OCF1x.
Figure 16-10. Timer/Counter Timing Diagram, Setting of OCF1x, no Prescaling
Figure 16-11 shows the same timing data, but with the prescaler enabled.
fOCnxPFCPWM
fclk_I/O
2NTOP⋅⋅
----------------------------=
clk
Tn
(clkI/O/1)
OCFnx
clk
I/O
OCRnx
TCNTn
OCRnx Value
OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2
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Figure 16-11. Timer/Counter Timing Diagram, Setting of OCF1x, with Prescaler (fclk_I/O/8)
Figure 16-12 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 16-12. Timer/Counter Timing Diagram, no Prescaling
Figure 16-13 shows the same timing data, but with the prescaler enabled.
OCFnx
OCRnx
TCNTn
OCRnx Value
OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2
clk
I/O
clk
Tn
(clk
I/O
/8)
TOVn (FPWM)
and ICFn (if used
as TOP)
OCRnx
(Update at TOP)
TCNTn
(CTC and FPWM)
TCNTn
(PC and PFC PWM) TOP - 1 TOP TOP - 1 TOP - 2
Old OCRnx Value New OCRnx Value
TOP - 1 TOP BOTTOM BOTTOM + 1
clk
Tn
(clk
I/O
/1)
clkI/O
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Figure 16-13. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
16.11 Register Description
16.11.1 TCCR1A – Timer/Counter1 Control Register A
• Bit 7:6 – COM1A1:0: Compare Output Mode for Unit A
• Bit 5:4 – COM1B1:0: Compare Output Mode for Unit B
The COM1A1:0 and COM1B1:0 control the Output Compare pins (OC1A and OC1B respec-
tively) 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 correspond-
ing 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 depen-
dent of the WGM13:0 bits setting. Table 16-2 shows the COM1x1:0 bit functionality when the
WGM13:0 bits are set to a Normal or a CTC mode (non-PWM).
TOVn (FPWM)
and ICFn (if used
as TOP)
OCRnx
(Update at TOP)
TCNTn
(CTC and FPWM)
TCNTn
(PC and PFC PWM) TOP - 1 TOP TOP - 1 TOP - 2
Old OCRnx Value New OCRnx Value
TOP - 1 TOP BOTTOM BOTTOM + 1
clk
I/O
clk
Tn
(clk
I/O
/8)
Bit 7 6 5 4 3210
(0x80) 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 16-2. Compare Output Mode, non-PWM
COM1A1/COM1B1 COM1A0/COM1B0 Description
00Normal 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).
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Table 16-3 shows the COM1x1:0 bit functionality when the WGM13:0 bits are set to the fast
PWM mode.
Note: 1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is set. In
this case the compare match is ignored, but the set or clear is done at BOTTOM. See “Fast
PWM Mode” on page 124. for more details.
Table 16-4 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.
Note: 1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is set. See
“Phase Correct PWM Mode” on page 126. for more details.
• 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 wave-
form generation to be used, see Table 16-5. Modes of operation supported by the Timer/Counter
unit are: Normal mode (counter), Clear Timer on Compare match (CTC) mode, and three types
of Pulse Width Modulation (PWM) modes. (See “Modes of Operation” on page 123.).
Table 16-3. Compare Output Mode, Fast PWM(1)
COM1A1/COM1B1 COM1A0/COM1B0 Description
00Normal port operation, OC1A/OC1B
disconnected.
0 1 WGM13:0 = 14 or 15: Toggle OC1A on Compare
Match, OC1B disconnected (normal port
operation). For all other WGM1 settings, normal
port operation, OC1A/OC1B disconnected.
1 0 Clear OC1A/OC1B on Compare Match, set
OC1A/OC1B at BOTTOM (non-inverting mode).
1 1 Set OC1A/OC1B on Compare Match, clear
OC1A/OC1B at BOTTOM (inverting mode).
Table 16-4. Compare Output Mode, Phase Correct and Phase and Frequency Correct
PWM(1)
COM1A1/COM1B1 COM1A0/COM1B0 Description
00Normal port operation, OC1A/OC1B
disconnected.
0 1 WGM13:0 = 9 or 11: Toggle OC1A on Compare
Match, OC1B disconnected (normal port
operation). For all other WGM1 settings, normal
port operation, OC1A/OC1B disconnected.
1 0 Clear OC1A/OC1B on Compare Match when up-
counting. Set OC1A/OC1B on Compare Match
when counting down.
1 1 Set OC1A/OC1B on Compare Match when up-
counting. Clear OC1A/OC1B on Compare Match
when counting down.
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Note: 1. The CTC1 and PWM11:0 bit definition names are obsolete. Use the WGM12:0 definitions. However, the functionality and
location of these bits are compatible with previous versions of the timer.
16.11.2 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.
Table 16-5. 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
00000Normal 0xFFFF Immediate MAX
10001PWM, 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
50101Fast 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
81 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
Bit 7654 3210
(0x81) 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
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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 Cap-
ture 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
16-10 and Figure 16-11.
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.
16.11.3 TCCR1C – Timer/Counter1 Control Register C
• Bit 7 – FOC1A: Force Output Compare for Unit A
• Bit 6 – FOC1B: Force Output Compare for Unit 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.
Table 16-6. Clock Select Bit Description
CS12 CS11 CS10 Description
000No clock source (Timer/Counter stopped).
001clk
I/O/1 (No prescaling)
010clk
I/O/8 (From prescaler)
011clk
I/O/64 (From prescaler)
100clk
I/O/256 (From prescaler)
101clk
I/O/1024 (From prescaler)
1 1 0 External clock source on T1 pin. Clock on falling edge.
1 1 1 External clock source on T1 pin. Clock on rising edge.
Bit 7654 3210
(0x82) FOC1A FOC1B – – – – – – TCCR1C
Read/Write R/W R/W R R R R R R
Initial Value 0 0 0 0 0 0 0 0
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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.
16.11.4 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 “Accessing 16-bit
Registers” on page 113.
Modifying the counter (TCNT1) while the counter is running introduces a risk of missing a com-
pare 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.
16.11.5 OCR1AH and OCR1AL – Output Compare Register 1 A
16.11.6 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 “Accessing 16-bit Registers” on page 113.
Bit 76543210
(0x85) TCNT1[15:8] TCNT1H
(0x84) 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
(0x89) OCR1A[15:8] OCR1AH
(0x88)OCR1A[7:0] OCR1AL
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
(0x8B) OCR1B[15:8] OCR1BH
(0x8A) OCR1B[7:0] OCR1BL
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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16.11.7 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. See “Accessing 16-bit Registers” on page 113.
16.11.8 TIMSK1 – Timer/Counter1 Interrupt Mask Register
• Bit 5 – ICIE1: Timer/Counter1, Input Capture Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter1 Input Capture interrupt is enabled. The corresponding Interrupt
Vector (See “Interrupts” on page 49.) 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 “Interrupts” on page 49.) 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 “Interrupts” on page 49.) is executed when the OCF1A Flag, located in
TIFR1, is set.
• Bit 0 – TOIE1: Timer/Counter1, Overflow Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter1 Overflow interrupt is enabled. The corresponding Interrupt Vector
(See “Interrupts” on page 49.) is executed when the TOV1 Flag, located in TIFR1, is set.
Bit 76543210
(0x87) ICR1[15:8] ICR1H
(0x86) ICR1[7:0] ICR1L
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
(0x6F) ––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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16.11.9 TIFR1 – Timer/Counter1 Interrupt Flag Register
• 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 coun-
ter 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 (FOC1B) strobe will not set the OCF1B Flag.
OCF1B is automatically cleared when the Output Compare Match B Interrupt Vector is exe-
cuted. Alternatively, OCF1B can be cleared by writing a logic one to its bit location.
Bit 1 – OCF1A: Timer/Counter1, Output Compare A Match Flag
This flag is set in the timer clock cycle after the counter (TCNT1) value matches the Output
Compare Register A (OCR1A).
Note that a Forced Output Compare (FOC1A) strobe will not set the OCF1A Flag.
OCF1A is automatically cleared when the Output Compare Match A Interrupt Vector is exe-
cuted. Alternatively, OCF1A can be cleared by writing a logic one to its bit location.
• Bit 0 – TOV1: Timer/Counter1, Overflow Flag
The setting of this flag is dependent of the WGM13:0 bits setting. In Normal and CTC modes,
the TOV1 Flag is set when the timer overflows. Refer to Table 16-5 on page 134 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 76543210
0x16 (0x36) ––ICF1–– OCF1B OCF1A TOV1 TIFR1
Read/Write R R R/W R R R/W R/W R/W
Initial Value00000000
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17. 8-bit Timer/Counter2 with PWM and Asynchronous Operation
17.1 Features
Timer/Counter2 is a general purpose, single compare unit, 8-bit Timer/Counter module. The
main features are:
•Single Compare Unit Counter
•Clear Timer on Compare Match (Auto Reload)
•Glitch-free, Phase Correct Pulse Width Modulator (PWM)
•Frequency Generator
•10-bit Clock Prescaler
•Overflow and Compare Match Interrupt Sources (TOV2 and OCF2A)
•Allows Clocking from External 32kHz Watch Crystal Independent of the I/O Clock
17.2 Overview
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 17-1. For the actual
placement of I/O pins, refer to “Pinout ATmega3290/6490” on page 2. CPU accessible I/O Reg-
isters, 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 “Register Description” on page 153.
Figure 17-1. 8-bit Timer/Counter Block Diagram
Timer/Counter
DATA B US
=
TCNTn
Waveform
Generation OCnx
= 0
Control Logic
= 0xFF
TOPBOTTOM
count
clear
direction
TOVn
(Int.Req.)
OCnx
(Int.Req.)
Synchronization Unit
OCRnx
TCCRnx
ASSRn
Status flags
clkI/O
clkASY
Synchronized Status flags
asynchronous mode
select (ASn)
TOSC1
T/C
Oscillator
TOSC2
Prescaler
clkTn
clkI/O
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17.2.1 Registers
The Timer/Counter (TCNT2) and Output Compare Register (OCR2A) are 8-bit registers. Inter-
rupt request (shorten as Int.Req.) signals are all visible in the Timer Interrupt Flag Register
(TIFR2). All interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK2).
TIFR2 and TIMSK2 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or asynchronously clocked from
the TOSC1/2 pins, as detailed later in this section. The asynchronous operation is controlled by
the Asynchronous Status Register (ASSR). The Clock Select logic block controls which clock
source the Timer/Counter uses to increment (or decrement) its value. The Timer/Counter is inac-
tive when no clock source is selected. The output from the Clock Select logic is referred to as the
timer clock (clkT2).
The double buffered Output Compare Register (OCR2A) is compared with the Timer/Counter
value at all times. The result of the compare can be used by the Waveform Generator to gener-
ate a PWM or variable frequency output on the Output Compare pin (OC2A). See “Output
Compare Unit” on page 141. for details. The compare match event will also set the Compare
Flag (OCF2A) which can be used to generate an Output Compare interrupt request.
17.2.2 Definitions
Many register and bit references in this document are written in general form. A lower case “n”
replaces the Timer/Counter number, in this case 2. However, when using the register or bit
defines in a program, the precise form must be used, i.e., TCNT2 for accessing Timer/Counter2
counter value and so on.
The definitions in Table 17-1 are also used extensively throughout the section.
17.3 Timer/Counter Clock Sources
The Timer/Counter can be clocked by an internal synchronous or an external asynchronous
clock source. The clock source clkT2 is by default equal to the MCU clock, clkI/O. When the AS2
bit in the ASSR Register is written to logic one, the clock source is taken from the Timer/Counter
Oscillator connected to TOSC1 and TOSC2. For details on asynchronous operation, see “ASSR
– Asynchronous Status Register” on page 155. For details on clock sources and prescaler, see
“Timer/Counter Prescaler” on page 152.
17.4 Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure
17-2 shows a block diagram of the counter and its surrounding environment.
Table 17-1. Definitions of Timer/Counter values.
BOTTOM The counter reaches the BOTTOM when it becomes zero (0x00).
MAX The counter reaches its MAXimum when it becomes 0xFF (decimal 255).
TOP The counter reaches the TOP when it becomes equal to the highest
value in the count sequence. The TOP value can be assigned to be the
fixed value 0xFF (MAX) or the value stored in the OCR2A Register. The
assignment is dependent on the mode of operation.
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Figure 17-2. Counter Unit Block Diagram
Signal description (internal signals):
count Increment or decrement TCNT2 by 1.
direction Selects between increment and decrement.
clear Clear TCNT2 (set all bits to zero).
clkT2Timer/Counter clock.
top Signalizes that TCNT2 has reached maximum value.
bottom Signalizes that TCNT2 has reached minimum value (zero).
Depending on the mode of operation used, the counter is cleared, incremented, or decremented
at each timer clock (clkT2). clkT2 can be generated from an external or internal clock source,
selected by the Clock Select bits (CS22:0). When no clock source is selected (CS22:0 = 0) the
timer is stopped. However, the TCNT2 value can be accessed by the CPU, regardless of
whether clkT2 is present or not. A CPU write overrides (has priority over) all counter clear or
count operations.
The counting sequence is determined by the setting of the WGM21 and WGM20 bits located in
the Timer/Counter Control Register (TCCR2A). There are close connections between how the
counter behaves (counts) and how waveforms are generated on the Output Compare output
OC2A. For more details about advanced counting sequences and waveform generation, see
“Modes of Operation” on page 145.
The Timer/Counter Overflow Flag (TOV2) is set according to the mode of operation selected by
the WGM21:0 bits. TOV2 can be used for generating a CPU interrupt.
17.5 Output Compare Unit
The 8-bit comparator continuously compares TCNT2 with the Output Compare Register
(OCR2A). Whenever TCNT2 equals OCR2A, the comparator signals a match. A match will set
the Output Compare Flag (OCF2A) at the next timer clock cycle. If enabled (OCIE2A = 1), the
Output Compare Flag generates an Output Compare interrupt. The OCF2A Flag is automatically
cleared when the interrupt is executed. Alternatively, the OCF2A Flag can be cleared by soft-
ware 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 WGM21:0 bits and Com-
pare Output mode (COM2A1:0) 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
(“Modes of Operation” on page 145).
Figure 17-3 shows a block diagram of the Output Compare unit.
DATA BUS
TCNTn Control Logic
count
TOVn
(Int.Req.)
topbottom
direction
clear
TOSC1
T/C
Oscillator
TOSC2
Prescaler
clk
I/O
clk
Tn
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Figure 17-3. Output Compare Unit, Block Diagram
The OCR2A Register is double buffered when using any of the Pulse Width Modulation (PWM)
modes. For the Normal and Clear Timer on Compare (CTC) modes of operation, the double
buffering is disabled. The double buffering synchronizes the update of the OCR2A 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 OCR2A Register access may seem complex, but this is not case. When the double buffer-
ing is enabled, the CPU has access to the OCR2A Buffer Register, and if double buffering is
disabled the CPU will access the OCR2A directly.
17.5.1 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 (FOC2A) bit. Forcing compare match will not set the
OCF2A Flag or reload/clear the timer, but the OC2A pin will be updated as if a real compare
match had occurred (the COM2A1:0 bits settings define whether the OC2A pin is set, cleared or
toggled).
17.5.2 Compare Match Blocking by TCNT2 Write
All CPU write operations to the TCNT2 Register will block any compare match that occurs in the
next timer clock cycle, even when the timer is stopped. This feature allows OCR2A to be initial-
ized to the same value as TCNT2 without triggering an interrupt when the Timer/Counter clock is
enabled.
17.5.3 Using the Output Compare Unit
Since writing TCNT2 in any mode of operation will block all compare matches for one timer clock
cycle, there are risks involved when changing TCNT2 when using the Output Compare unit,
independently of whether the Timer/Counter is running or not. If the value written to TCNT2
equals the OCR2A value, the compare match will be missed, resulting in incorrect waveform
generation. Similarly, do not write the TCNT2 value equal to BOTTOM when the counter is
counting down.
OCFnx (Int.Req.)
= (8-bit Comparator )
OCRnx
OCnx
DATA B U S
TCNTn
WGMn1:0
Waveform Generator
top
FOCn
COMnX1:0
bottom
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The setup of the OC2A should be performed before setting the Data Direction Register for the
port pin to output. The easiest way of setting the OC2A value is to use the Force Output Com-
pare (FOC2A) strobe bit in Normal mode. The OC2A Register keeps its value even when
changing between Waveform Generation modes.
Be aware that the COM2A1:0 bits are not double buffered together with the compare value.
Changing the COM2A1:0 bits will take effect immediately.
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17.6 Compare Match Output Unit
The Compare Output mode (COM2A1:0) bits have two functions. The Waveform Generator
uses the COM2A1:0 bits for defining the Output Compare (OC2A) state at the next compare
match. Also, the COM2A1:0 bits control the OC2A pin output source. Figure 17-4 shows a sim-
plified schematic of the logic affected by the COM2A1:0 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 Regis-
ters (DDR and PORT) that are affected by the COM2A1:0 bits are shown. When referring to the
OC2A state, the reference is for the internal OC2A Register, not the OC2A pin.
Figure 17-4. Compare Match Output Unit, Schematic
The general I/O port function is overridden by the Output Compare (OC2A) from the Waveform
Generator if either of the COM2A1:0 bits are set. However, the OC2A pin direction (input or out-
put) is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction
Register bit for the OC2A pin (DDR_OC2A) must be set as output before the OC2A value is vis-
ible 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 OC2A state before the
output is enabled. Note that some COM2A1:0 bit settings are reserved for certain modes of
operation. See “Register Description” on page 153.
17.6.1 Compare Output Mode and Waveform Generation
The Waveform Generator uses the COM2A1:0 bits differently in normal, CTC, and PWM modes.
For all modes, setting the COM2A1:0 = 0 tells the Waveform Generator that no action on the
OC2A Register is to be performed on the next compare match. For compare output actions in
the non-PWM modes refer to Table 17-3 on page 154. For fast PWM mode, refer to Table 17-4
on page 154, and for phase correct PWM refer to Table 17-5 on page 154.
PORT
DDR
DQ
DQ
OCnx
Pin
OCnx
DQ
Waveform
Generator
COMnx1
COMnx0
0
1
DATA BU S
FOCnx
clk
I/O
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A change of the COM2A1:0 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
FOC2A strobe bits.
17.7 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 (WGM21:0) and Compare Output
mode (COM2A1:0) bits. The Compare Output mode bits do not affect the counting sequence,
while the Waveform Generation mode bits do. The COM2A1:0 bits control whether the PWM
output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM
modes the COM2A1:0 bits control whether the output should be set, cleared, or toggled at a
compare match (See “Compare Match Output Unit” on page 144.).
For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 149.
17.7.1 Normal Mode
The simplest mode of operation is the Normal mode (WGM21:0 = 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 bot-
tom (0x00). In normal operation the Timer/Counter Overflow Flag (TOV2) will be set in the same
timer clock cycle as the TCNT2 becomes zero. The TOV2 Flag in this case behaves like a ninth
bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt
that automatically clears the TOV2 Flag, the timer resolution can be increased by software.
There are no special cases to consider in the Normal mode, a new counter value can be written
anytime.
The Output Compare unit can be used to generate interrupts at some given time. Using the Out-
put Compare to generate waveforms in Normal mode is not recommended, since this will
occupy too much of the CPU time.
17.7.2 Clear Timer on Compare Match (CTC) Mode
In Clear Timer on Compare or CTC mode (WGM21:0 = 2), the OCR2A Register is used to
manipulate the counter resolution. In CTC mode the counter is cleared to zero when the counter
value (TCNT2) matches the OCR2A. The OCR2A defines the top value for the counter, hence
also its resolution. This mode allows greater control of the compare match output frequency. It
also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 17-5. The counter value (TCNT2)
increases until a compare match occurs between TCNT2 and OCR2A, and then counter
(TCNT2) is cleared.
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Figure 17-5. CTC Mode, Timing Diagram
An interrupt can be generated each time the counter value reaches the TOP value by using the
OCF2A Flag. If the interrupt is enabled, the interrupt handler routine can be used for updating
the TOP value. However, changing 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 OCR2A is lower than the cur-
rent value of TCNT2, the counter will miss the compare match. The counter will then have to
count to its maximum value (0xFF) and wrap around starting at 0x00 before the compare match
can occur.
For generating a waveform output in CTC mode, the OC2A output can be set to toggle its logical
level on each compare match by setting the Compare Output mode bits to toggle mode
(COM2A1:0 = 1). The OC2A value will not be visible on the port pin unless the data direction for
the pin is set to output. The waveform generated will have a maximum frequency of fOC2A =
fclk_I/O/2 when OCR2A is set to zero (0x00). The waveform frequency is defined by the following
equation:
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
As for the Normal mode of operation, the TOV2 Flag is set in the same timer clock cycle that the
counter counts from MAX to 0x00.
17.7.3 Fast PWM Mode
The fast Pulse Width Modulation or fast PWM mode (WGM21:0 = 3) provides a high frequency
PWM waveform generation option. The fast PWM differs from the other PWM option by its sin-
gle-slope operation. The counter counts from BOTTOM to MAX then restarts from BOTTOM. In
non-inverting Compare Output mode, the Output Compare (OC2A) is cleared on the compare
match between TCNT2 and OCR2A, and set at BOTTOM. In inverting Compare Output mode,
the output is set on compare match and cleared at BOTTOM. Due to the single-slope operation,
the operating frequency of the fast PWM mode can be twice as high as the phase correct PWM
mode that uses dual-slope operation. This high frequency makes the fast PWM mode well suited
for power regulation, rectification, and DAC applications. High frequency allows physically small
sized external components (coils, capacitors), and therefore reduces total system cost.
In fast PWM mode, the counter is incremented until the counter value matches the MAX value.
The counter is then cleared at the following timer clock cycle. The timing diagram for the fast
TCNTn
OCnx
(Toggle)
OCnx Interrupt Flag Set
1 4
Period
2 3
(COMnx1:0 = 1)
fOCnx
fclk_I/O
2N1OCRnx+()⋅⋅
--------------------------------------------------=
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PWM mode is shown in Figure 17-6. The TCNT2 value is in the timing diagram shown as a his-
togram for illustrating the single-slope operation. The diagram includes non-inverted and
inverted PWM outputs. The small horizontal line marks on the TCNT2 slopes represent compare
matches between OCR2A and TCNT2.
Figure 17-6. Fast PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV2) is set each time the counter reaches MAX. If the inter-
rupt 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 OC2A pin.
Setting the COM2A1:0 bits to two will produce a non-inverted PWM and an inverted PWM output
can be generated by setting the COM2A1:0 to three (See Table 17-4 on page 154). The actual
OC2A value will only be visible on the port pin if the data direction for the port pin is set as out-
put. The PWM waveform is generated by setting (or clearing) the OC2A Register at the compare
match between OCR2A and TCNT2, and clearing (or setting) the OC2A Register at the timer
clock cycle the counter is cleared (changes from MAX to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
The extreme values for the OCR2A Register represent special cases when generating a PWM
waveform output in the fast PWM mode. If the OCR2A is set equal to BOTTOM, the output will
be a narrow spike for each MAX+1 timer clock cycle. Setting the OCR2A equal to MAX will result
in a constantly high or low output (depending on the polarity of the output set by the COM2A1:0
bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by set-
ting OC2A to toggle its logical level on each compare match (COM2A1:0 = 1). The waveform
generated will have a maximum frequency of foc2 = fclk_I/O/2 when OCR2A is set to zero. This fea-
ture is similar to the OC2A toggle in CTC mode, except the double buffer feature of the Output
Compare unit is enabled in the fast PWM mode.
TCNTn
OCRnx Update and
TOVn Interrupt Flag Set
1
Period
2 3
OCnx
OCnx
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCRnx Interrupt Flag Set
4 5 6 7
fOCnxPWM
fclk_I/O
N256⋅
------------------=
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17.7.4 Phase Correct PWM Mode
The phase correct PWM mode (WGM21:0 = 1) 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 MAX and then from MAX to BOTTOM. In non-
inverting Compare Output mode, the Output Compare (OC2A) is cleared on the compare match
between TCNT2 and OCR2A while counting up, and set on the compare match while counting
down. 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 sym-
metric feature of the dual-slope PWM modes, these modes are preferred for motor control
applications.
The PWM resolution for the phase correct PWM mode is fixed to eight bits. In phase correct
PWM mode the counter is incremented until the counter value matches MAX. When the counter
reaches MAX, it changes the count direction. The TCNT2 value will be equal to MAX for one
timer clock cycle. The timing diagram for the phase correct PWM mode is shown on Figure 17-7.
The TCNT2 value is in the timing diagram shown as a histogram for illustrating the dual-slope
operation. The diagram includes non-inverted and inverted PWM outputs. The small horizontal
line marks on the TCNT2 slopes represent compare matches between OCR2A and TCNT2.
Figure 17-7. Phase Correct PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV2) is set each time the counter reaches BOTTOM. The
Interrupt Flag can be used to generate an interrupt each time the counter reaches the BOTTOM
value.
In phase correct PWM mode, the compare unit allows generation of PWM waveforms on the
OC2A pin. Setting the COM2A1:0 bits to two will produce a non-inverted PWM. An inverted
PWM output can be generated by setting the COM2A1:0 to three (See Table 17-5 on page 154).
The actual OC2A 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 OC2A Register at the
compare match between OCR2A and TCNT2 when the counter increments, and setting (or
clearing) the OC2A Register at compare match between OCR2A and TCNT2 when the counter
TOVn Interrupt Flag Set
OCnx Interrupt Flag Set
1 2 3
TCNTn
Period
OCnx
OCnx
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCRnx Update
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decrements. The PWM frequency for the output when using phase correct PWM can be calcu-
lated by the following equation:
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
The extreme values for the OCR2A Register represent special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCR2A is set equal to BOTTOM, the
output will be continuously low and if set equal to MAX the output will be continuously high for
non-inverted PWM mode. For inverted PWM the output will have the opposite logic values.
At the very start of period 2 in Figure 17-7 OCn has a transition from high to low even though
there is no Compare Match. The point of this transition is to guarantee symmetry around BOT-
TOM. There are two cases that give a transition without Compare Match.
• OCR2A changes its value from MAX, like in Figure 17-7. When the OCR2A value is MAX the
OCn pin value is the same as the result of a down-counting compare match. To ensure
symmetry around BOTTOM the OCn value at MAX must correspond to the result of an up-
counting Compare Match.
• The timer starts counting from a value higher than the one in OCR2A, and for that reason
misses the Compare Match and hence the OCn change that would have happened on the
way up.
17.8 Timer/Counter Timing Diagrams
The following figures show the Timer/Counter in synchronous mode, and the timer clock (clkT2)
is therefore shown as a clock enable signal. In asynchronous mode, clkI/O should be replaced by
the Timer/Counter Oscillator clock. The figures include information on when Interrupt Flags are
set. Figure 17-8 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 17-8. Timer/Counter Timing Diagram, no Prescaling
Figure 17-9 shows the same timing data, but with the prescaler enabled.
fOCnxPCPWM
fclk_I/O
N510⋅
------------------=
clk
Tn
(clk
I/O
/1)
TOVn
clk
I/O
TCNTn MAX - 1 MAX BOTTOM BOTTOM + 1
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Figure 17-9. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
Figure 17-10 shows the setting of OCF2A in all modes except CTC mode.
Figure 17-10. Timer/Counter Timing Diagram, Setting of OCF2A, with Prescaler (fclk_I/O/8)
Figure 17-11 shows the setting of OCF2A and the clearing of TCNT2 in CTC mode.
Figure 17-11. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with Pres-
caler (fclk_I/O/8)
TOVn
TCNTn MAX - 1 MAX BOTTOM BOTTOM + 1
clk
I/O
clk
Tn
(clk
I/O
/8)
OCFnx
OCRnx
TCNTn
OCRnx Value
OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2
clk
I/O
clk
Tn
(clk
I/O
/8)
OCFnx
OCRnx
TCNTn
(CTC)
TOP
TOP - 1 TOP BOTTOM BOTTOM + 1
clk
I/O
clk
Tn
(clk
I/O
/8)
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17.9 Asynchronous Operation of Timer/Counter2
When Timer/Counter2 operates asynchronously, some considerations must be taken.
• Warning: When switching between asynchronous and synchronous clocking of
Timer/Counter2, the Timer Registers TCNT2, OCR2A, and TCCR2A might be corrupted. A
safe procedure for switching clock source is:
1. Disable the Timer/Counter2 interrupts by clearing OCIE2A and TOIE2.
2. Select clock source by setting AS2 as appropriate.
3. Write new values to TCNT2, OCR2A, and TCCR2A.
4. To switch to asynchronous operation: Wait for TCN2UB, OCR2UB, and TCR2UB.
5. Clear the Timer/Counter2 Interrupt Flags.
6. Enable interrupts, if needed.
• The CPU main clock frequency must be more than four times the Oscillator frequency.
• When writing to one of the registers TCNT2, OCR2A, or TCCR2A, the value is transferred to
a temporary register, and latched after two positive edges on TOSC1. The user should not
write a new value before the contents of the temporary register have been transferred to its
destination. Each of the three mentioned registers have their individual temporary register,
which means that e.g. writing to TCNT2 does not disturb an OCR2A write in progress. To
detect that a transfer to the destination register has taken place, the Asynchronous Status
Register – ASSR has been implemented.
• When entering Power-save or ADC Noise Reduction mode after having written to TCNT2,
OCR2A, or TCCR2A, the user must wait until the written register has been updated if
Timer/Counter2 is used to wake up the device. Otherwise, the MCU will enter sleep mode
before the changes are effective. This is particularly important if the Output Compare2
interrupt is used to wake up the device, since the Output Compare function is disabled
during writing to OCR2A or TCNT2. If the write cycle is not finished, and the MCU enters
sleep mode before the OCR2UB bit returns to zero, the device will never receive a compare
match interrupt, and the MCU will not wake up.
• If Timer/Counter2 is used to wake the device up from Power-save or ADC Noise Reduction
mode, precautions must be taken if the user wants to re-enter one of these modes: The
interrupt logic needs one TOSC1 cycle to be reset. If the time between wake-up and re-
entering sleep mode is less than one TOSC1 cycle, the interrupt will not occur, and the
device will fail to wake up. If the user is in doubt whether the time before re-entering Power-
save or ADC Noise Reduction mode is sufficient, the following algorithm can be used to
ensure that one TOSC1 cycle has elapsed:
1. Write a value to TCCR2A, TCNT2, or OCR2A.
2. Wait until the corresponding Update Busy Flag in ASSR returns to zero.
3. Enter Power-save or ADC Noise Reduction mode.
• When the asynchronous operation is selected, the 32.768kHz Oscillator for Timer/Counter2
is always running, except in Power-down and Standby modes. After a Power-up Reset or
wake-up from Power-down or Standby mode, the user should be aware of the fact that this
Oscillator might take as long as one second to stabilize. The user is advised to wait for at
least one second before using Timer/Counter2 after power-up or wake-up from Power-down
or Standby mode. The contents of all Timer/Counter2 Registers must be considered lost
after a wake-up from Power-down or Standby mode due to unstable clock signal upon start-
up, no matter whether the Oscillator is in use or a clock signal is applied to the TOSC1 pin.
• Description of wake up from Power-save or ADC Noise Reduction mode when the timer is
clocked asynchronously: When the interrupt condition is met, the wake up process is started
on the following cycle of the timer clock, that is, the timer is always advanced by at least one
before the processor can read the counter value. After wake-up, the MCU is halted for four
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cycles, it executes the interrupt routine, and resumes execution from the instruction
following SLEEP.
• Reading of the TCNT2 Register shortly after wake-up from Power-save may give an
incorrect result. Since TCNT2 is clocked on the asynchronous TOSC clock, reading TCNT2
must be done through a register synchronized to the internal I/O clock domain.
Synchronization takes place for every rising TOSC1 edge. When waking up from Power-
save mode, and the I/O clock (clkI/O) again becomes active, TCNT2 will read as the previous
value (before entering sleep) until the next rising TOSC1 edge. The phase of the TOSC
clock after waking up from Power-save mode is essentially unpredictable, as it depends on
the wake-up time. The recommended procedure for reading TCNT2 is thus as follows:
1. Write any value to either of the registers OCR2A or TCCR2A.
2. Wait for the corresponding Update Busy Flag to be cleared.
3. Read TCNT2.
During asynchronous operation, the synchronization of the Interrupt Flags for the asynchronous
timer takes 3 processor cycles plus one timer cycle. The timer is therefore advanced by at least
one before the processor can read the timer value causing the setting of the Interrupt Flag. The
Output Compare pin is changed on the timer clock and is not synchronized to the processor
clock.
17.10 Timer/Counter Prescaler
Figure 17-12. Prescaler for Timer/Counter2
The clock source for Timer/Counter2 is named clkT2S. clkT2S is by default connected to the main
system I/O clock clkIO. By setting the AS2 bit in ASSR, Timer/Counter2 is asynchronously
clocked from the TOSC1 pin. This enables use of Timer/Counter2 as a Real Time Counter
(RTC). When AS2 is set, pins TOSC1 and TOSC2 are disconnected from Port C. A crystal can
then be connected between the TOSC1 and TOSC2 pins to serve as an independent clock
source for Timer/Counter2. The Oscillator is optimized for use with a 32.768kHz crystal. If apply-
ing an external clock on TOSC1, the EXCLK bit in ASSR must be set.
10-BIT T/C PRESCALER
TIMER/COUNTER2 CLOCK SOURCE
clkI/O clkT2S
TOSC1
AS2
CS20
CS21
CS22
clkT2S
/8
clkT2S
/64
clkT2S
/128
clkT2S
/1024
clkT2S
/256
clkT2S
/32
0
PSR2
Clear
clkT2
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For Timer/Counter2, the possible prescaled selections are: clkT2S/8, clkT2S/32, clkT2S/64,
clkT2S/128, clkT2S/256, and clkT2S/1024. Additionally, clkT2S as well as 0 (stop) may be selected.
Setting the PSR2 bit in GTCCR resets the prescaler. This allows the user to operate with a pre-
dictable prescaler.
17.11 Register Description
17.11.1 TCCR2A – Timer/Counter Control Register A
• Bit 7 – FOC2A: Force Output Compare A
The FOC2A bit is only active when the WGM bits specify a non-PWM mode. However, for ensur-
ing compatibility with future devices, this bit must be set to zero when TCCR2A is written when
operating in PWM mode. When writing a logical one to the FOC2A bit, an immediate compare
match is forced on the Waveform Generation unit. The OC2A output is changed according to its
COM2A1:0 bits setting. Note that the FOC2A bit is implemented as a strobe. Therefore it is the
value present in the COM2A1:0 bits that determines the effect of the forced compare.
A FOC2A strobe will not generate any interrupt, nor will it clear the timer in CTC mode using
OCR2A as TOP.
The FOC2A bit is always read as zero.
• Bit 6, 3 – WGM21:0: Waveform Generation Mode
These bits control the counting sequence of the counter, the source for the maximum (TOP)
counter value, and what type of waveform generation to be used. Modes of operation supported
by the Timer/Counter unit are: Normal mode, Clear Timer on Compare match (CTC) mode, and
two types of Pulse Width Modulation (PWM) modes. See Table 17-2 and “Modes of Operation”
on page 145.
Note: 1. The CTC2 and PWM2 bit definition names are now obsolete. Use the WGM21:0 definitions.
However, the functionality and location of these bits are compatible with previous versions of
the timer.
• Bit 5:4 – COM2A1:0: Compare Match Output Mode A
These bits control the Output Compare pin (OC2A) behavior. If one or both of the COM2A1:0
bits are set, the OC2A output overrides the normal port functionality of the I/O pin it is connected
to. However, note that the Data Direction Register (DDR) bit corresponding to OC2A pin must be
set in order to enable the output driver.
Bit 7 6 5 4 3 2 1 0
(0xB0) FOC2A WGM20 COM2A1 COM2A0 WGM21 CS22 CS21 CS20 TCCR2A
Read/Write W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 17-2. Waveform Generation Mode Bit Description(1)
Mode
WGM21
(CTC2)
WGM20
(PWM2)
Timer/Counter Mode
of Operation TOP
Update of
OCR2A at
TOV2 Flag
Set on
00 0Normal 0xFF Immediate MAX
1 0 1 PWM, Phase Correct 0xFF TOP BOTTOM
2 1 0 CTC OCR2A Immediate MAX
31 1Fast PWM 0xFFBOTTOMMAX
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When OC2A is connected to the pin, the function of the COM2A1:0 bits depends on the
WGM21:0 bit setting. Table 17-3 shows the COM2A1:0 bit functionality when the WGM21:0 bits
are set to a normal or CTC mode (non-PWM).
Table 17-4 shows the COM2A1:0 bit functionality when the WGM21:0 bits are set to fast PWM
mode.
Note: 1. A special case occurs when OCR2A equals TOP and COM2A1 is set. In this case, the com-
pare match is ignored, but the set or clear is done at BOTTOM. See “Fast PWM Mode” on
page 146 for more details.
Table 17-5 shows the COM21:0 bit functionality when the WGM21:0 bits are set to phase cor-
rect PWM mode.
Note: 1. A special case occurs when OCR2A equals TOP and COM2A1 is set. In this case, the com-
pare match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on
page 148 for more details.
Table 17-3. Compare Output Mode, non-PWM Mode
COM2A1 COM2A0 Description
00Normal port operation, OC2A disconnected.
0 1 Toggle OC2A on compare match.
1 0 Clear OC2A on compare match.
1 1 Set OC2A on compare match.
Table 17-4. Compare Output Mode, Fast PWM Mode(1)
COM2A1 COM2A0 Description
00Normal port operation, OC2A disconnected.
01Reserved
1 0 Clear OC2A on compare match, set OC2A at BOTTOM,
(non-inverting mode).
1 1 Set OC2A on compare match, clear OC2A at BOTTOM,
(inverting mode)
Table 17-5. Compare Output Mode, Phase Correct PWM Mode(1)
COM2A1 COM2A0 Description
00Normal port operation, OC2A disconnected.
01Reserved
1 0 Clear OC2A on compare match when up-counting. Set OC2A on
compare match when counting down.
1 1 Set OC2A on compare match when up-counting. Clear OC2A on
compare match when counting down.
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• Bit 2:0 – CS22:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter, see Table
17-6.
17.11.2 TCNT2 – 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 TCNT2 Register blocks (removes) the compare
match on the following timer clock. Modifying the counter (TCNT2) while the counter is running,
introduces a risk of missing a compare match between TCNT2 and the OCR2A Register.
17.11.3 OCR2A – Output Compare Register A
The Output Compare Register A contains an 8-bit value that is continuously compared with the
counter value (TCNT2). A match can be used to generate an Output Compare interrupt, or to
generate a waveform output on the OC2A pin.
17.11.4 ASSR – Asynchronous Status Register
• Bit 4 – EXCLK: Enable External Clock Input
When EXCLK is written to one, and asynchronous clock is selected, the external clock input buf-
fer is enabled and an external clock can be input on Timer Oscillator 1 (TOSC1) pin instead of a
32kHz crystal. Writing to EXCLK should be done before asynchronous operation is selected.
Note that the crystal Oscillator will only run when this bit is zero.
Table 17-6. Clock Select Bit Description
CS22 CS21 CS20 Description
000No clock source (Timer/Counter stopped).
001clk
T2S/(No prescaling)
010clk
T2S/8 (From prescaler)
011clk
T2S/32 (From prescaler)
100clk
T2S/64 (From prescaler)
101clk
T2S/128 (From prescaler)
110clk
T2S/256 (From prescaler)
111clk
T2S/1024 (From prescaler)
Bit 76543210
(0xB2) TCNT2[7:0] TCNT2
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
(0xB3) OCR2A[7:0] OCR2A
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 765 4 3 2 1 0
(0xB6) ––– EXCLK AS2 TCN2UB OCR2UB TCR2UB ASSR
Read/Write R R R R/W R/W R R R
Initial Value 0 0 0 0 0 0 0 0
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• Bit 3 – AS2: Asynchronous Timer/Counter2
When AS2 is written to zero, Timer/Counter2 is clocked from the I/O clock, clkI/O. When AS2 is
written to one, Timer/Counter2 is clocked from a crystal Oscillator connected to the Timer Oscil-
lator 1 (TOSC1) pin. When the value of AS2 is changed, the contents of TCNT2, OCR2A, and
TCCR2A might be corrupted.
• Bit 2 – TCN2UB: Timer/Counter2 Update Busy
When Timer/Counter2 operates asynchronously and TCNT2 is written, this bit becomes set.
When TCNT2 has been updated from the temporary storage register, this bit is cleared by hard-
ware. A logical zero in this bit indicates that TCNT2 is ready to be updated with a new value.
• Bit 1 – OCR2UB: Output Compare Register2 Update Busy
When Timer/Counter2 operates asynchronously and OCR2A is written, this bit becomes set.
When OCR2A has been updated from the temporary storage register, this bit is cleared by hard-
ware. A logical zero in this bit indicates that OCR2A is ready to be updated with a new value.
• Bit 0 – TCR2UB: Timer/Counter Control Register2 Update Busy
When Timer/Counter2 operates asynchronously and TCCR2A is written, this bit becomes set.
When TCCR2A has been updated from the temporary storage register, this bit is cleared by
hardware. A logical zero in this bit indicates that TCCR2A is ready to be updated with a new
value.
If a write is performed to any of the three Timer/Counter2 Registers while its update busy flag is
set, the updated value might get corrupted and cause an unintentional interrupt to occur.
The mechanisms for reading TCNT2, OCR2A, and TCCR2A are different. When reading
TCNT2, the actual timer value is read. When reading OCR2A or TCCR2A, the value in the tem-
porary storage register is read.
17.11.5 TIMSK2 – Timer/Counter2 Interrupt Mask Register
• Bit 1 – OCIE2A: Timer/Counter2 Output Compare Match A Interrupt Enable
When the OCIE2A bit is written to one and the I-bit in the Status Register is set (one), the
Timer/Counter2 Compare Match A interrupt is enabled. The corresponding interrupt is executed
if a compare match in Timer/Counter2 occurs, i.e., when the OCF2A bit is set in the Timer/Coun-
ter 2 Interrupt Flag Register – TIFR2.
• Bit 0 – TOIE2: Timer/Counter2 Overflow Interrupt Enable
When the TOIE2 bit is written to one and the I-bit in the Status Register is set (one), the
Timer/Counter2 Overflow interrupt is enabled. The corresponding interrupt is executed if an
overflow in Timer/Counter2 occurs, i.e., when the TOV2 bit is set in the Timer/Counter2 Interrupt
Flag Register – TIFR2.
Bit 76543210
(0x70) –––––– OCIE2A TOIE2 TIMSK2
Read/WriteRRRRRRR/WR/W
Initial Value 0 0 0 0 0 0 0 0
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17.11.6 TIFR2 – Timer/Counter2 Interrupt Flag Register
• Bit 1 – OCF2A: Output Compare Flag 2 A
The OCF2A bit is set (one) when a compare match occurs between the Timer/Counter2 and the
data in OCR2A – Output Compare Register2. OCF2A is cleared by hardware when executing
the corresponding interrupt handling vector. Alternatively, OCF2A is cleared by writing a logic
one to the flag. When the I-bit in SREG, OCIE2A (Timer/Counter2 Compare match Interrupt
Enable), and OCF2A are set (one), the Timer/Counter2 Compare match Interrupt is executed.
• Bit 0 – TOV2: Timer/Counter2 Overflow Flag
The TOV2 bit is set (one) when an overflow occurs in Timer/Counter2. TOV2 is cleared by hard-
ware when executing the corresponding interrupt handling vector. Alternatively, TOV2 is cleared
by writing a logic one to the flag. When the SREG I-bit, TOIE2A (Timer/Counter2 Overflow Inter-
rupt Enable), and TOV2 are set (one), the Timer/Counter2 Overflow interrupt is executed. In
PWM mode, this bit is set when Timer/Counter2 changes counting direction at 0x00.
17.11.7 GTCCR – General Timer/Counter Control Register
• Bit 1 – PSR2: Prescaler Reset Timer/Counter2
When this bit is one, the Timer/Counter2 prescaler will be reset. This bit is normally cleared
immediately by hardware. If the bit is written when Timer/Counter2 is operating in asynchronous
mode, the bit will remain one until the prescaler has been reset. The bit will not be cleared by
hardware if the TSM bit is set. Refer to the description of the “Bit 7 – TSM: Timer/Counter Syn-
chronization Mode” on page 108 for a description of the Timer/Counter Synchronization mode.
Bit 76543210
0x17 (0x37) –––––– OCF2A TOV2 TIFR2
Read/WriteRRRRRRR/WR/W
Initial Value00000000
Bit 7 6 5 4 3 2 1 0
0x23 (0x43) TSM – – – – – PSR2 PSR10 GTCCR
Read/Write R/W R R R R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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18. SPI – Serial Peripheral Interface
18.1 Features
The ATmega329/3290/649/6490 SPI includes the following features:
•Full-duplex, Three-wire Synchronous Data Transfer
•Master or Slave Operation
•LSB First or MSB First Data Transfer
•Seven Programmable Bit Rates
•End of Transmission Interrupt Flag
•Write Collision Flag Protection
•Wake-up from Idle Mode
•Double Speed (CK/2) Master SPI Mode
18.2 Overview
The Serial Peripheral Interface (SPI) allows high-speed synchronous data transfer between the
ATmega329/3290/649/6490 and peripheral devices or between several AVR devices. A simpli-
fied block diagram of the Serial Peripheral Interface is shown in Figure 18-1.
The PRSPI bit in “Power Reduction Register” on page 37 must be written to zero to enable the
SPI module.
Figure 18-1. SPI Block Diagram(1)
Note: 1. Refer to Figure 1-1 on page 2, and Table 13-6 on page 68 for SPI pin placement.
SPI2X
SPI2X
DIVIDER
/2/4/8/16/32/64/128
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The interconnection between Master and Slave CPUs with SPI is shown in Figure 18-2. The sys-
tem consists of two shift Registers, and a Master clock generator. The SPI Master initiates the
communication cycle when pulling low the Slave Select SS pin of the desired Slave. Master and
Slave prepare the data to be sent in their respective shift Registers, and the Master generates
the required clock pulses on the SCK line to interchange data. Data is always shifted from Mas-
ter to Slave on the Master Out – Slave In, MOSI, line, and from Slave to Master on the Master In
– Slave Out, MISO, line. After each data packet, the Master will synchronize the Slave by pulling
high the Slave Select, SS, line.
When configured as a Master, the SPI interface has no automatic control of the SS line. This
must be handled by user software before communication can start. When this is done, writing a
byte to the SPI Data Register starts the SPI clock generator, and the hardware shifts the eight
bits into the Slave. After shifting one byte, the SPI clock generator stops, setting the end of
Transmission Flag (SPIF). If the SPI Interrupt Enable bit (SPIE) in the SPCR Register is set, an
interrupt is requested. The Master may continue to shift the next byte by writing it into SPDR, or
signal the end of packet by pulling high the Slave Select, SS line. The last incoming byte will be
kept in the Buffer Register for later use.
When configured as a Slave, the SPI interface will remain sleeping with MISO tri-stated as long
as the SS pin is driven high. In this state, software may update the contents of the SPI Data
Register, SPDR, but the data will not be shifted out by incoming clock pulses on the SCK pin
until the SS pin is driven low. As one byte has been completely shifted, the end of Transmission
Flag, SPIF is set. If the SPI Interrupt Enable bit, SPIE, in the SPCR Register is set, an interrupt
is requested. The Slave may continue to place new data to be sent into SPDR before reading
the incoming data. The last incoming byte will be kept in the Buffer Register for later use.
Figure 18-2. SPI Master-slave Interconnection
The system is single buffered in the transmit direction and double buffered in the receive direc-
tion. This means that bytes to be transmitted cannot be written to the SPI Data Register before
the entire shift cycle is completed. When receiving data, however, a received character must be
read from the SPI Data Register before the next character has been completely shifted in. Oth-
erwise, the first byte is lost.
In SPI Slave mode, the control logic will sample the incoming signal of the SCK pin. To ensure
correct sampling of the clock signal, the minimum low and high period should be:
Low period: longer than 2 CPU clock cycles.
High period: longer than 2 CPU clock cycles.
SHIFT
ENABLE
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When the SPI is enabled, the data direction of the MOSI, MISO, SCK, and SS pins is overridden
according to Table 18-1. For more details on automatic port overrides, refer to “Alternate Port
Functions” on page 65.
Note: 1. See “Alternate Functions of Port B” on page 68 for a detailed description of how to define the
direction of the user defined SPI pins.
Table 18-1. SPI Pin Overrides(1)
Pin Direction, Master SPI Direction, Slave SPI
MOSI User Defined Input
MISO Input User Defined
SCK User Defined Input
SS User Defined Input
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The following code examples show how to initialize the SPI as a Master and how to perform a
simple transmission. DDR_SPI in the examples must be replaced by the actual Data Direction
Register controlling the SPI pins. DD_MOSI, DD_MISO and DD_SCK must be replaced by the
actual data direction bits for these pins. E.g. if MOSI is placed on pin PB5, replace DD_MOSI
with DDB5 and DDR_SPI with DDRB.
Note: 1. See “About Code Examples” on page 9.
Assembly Code Example(1)
SPI_MasterInit:
; Set MOSI and SCK output, all others input
ldi r17,(1<<DD_MOSI)|(1<<DD_SCK)
out DDR_SPI,r17
; Enable SPI, Master, set clock rate fck/16
ldi r17,(1<<SPE)|(1<<MSTR)|(1<<SPR0)
out SPCR,r17
ret
SPI_MasterTransmit:
; Start transmission of data (r16)
out SPDR,r16
Wait_Transmit:
; Wait for transmission complete
sbis SPSR,SPIF
rjmp Wait_Transmit
ret
C Code Example(1)
void SPI_MasterInit(void)
{
/* Set MOSI and SCK output, all others input */
DDR_SPI = (1<<DD_MOSI)|(1<<DD_SCK);
/* Enable SPI, Master, set clock rate fck/16 */
SPCR = (1<<SPE)|(1<<MSTR)|(1<<SPR0);
}
void SPI_MasterTransmit(char cData)
{
/* Start transmission */
SPDR = cData;
/* Wait for transmission complete */
while(!(SPSR & (1<<SPIF)))
;
}
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The following code examples show how to initialize the SPI as a Slave and how to perform a
simple reception.
Note: 1. See “About Code Examples” on page 9.
Assembly Code Example(1)
SPI_SlaveInit:
; Set MISO output, all others input
ldi r17,(1<<DD_MISO)
out DDR_SPI,r17
; Enable SPI
ldi r17,(1<<SPE)
out SPCR,r17
ret
SPI_SlaveReceive:
; Wait for reception complete
sbis SPSR,SPIF
rjmp SPI_SlaveReceive
; Read received data and return
in r16,SPDR
ret
C Code Example(1)
void SPI_SlaveInit(void)
{
/* Set MISO output, all others input */
DDR_SPI = (1<<DD_MISO);
/* Enable SPI */
SPCR = (1<<SPE);
}
char SPI_SlaveReceive(void)
{
/* Wait for reception complete */
while(!(SPSR & (1<<SPIF)))
;
/* Return Data Register */
return SPDR;
}
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18.3 SS Pin Functionality
18.3.1 Slave Mode
When the SPI is configured as a Slave, the Slave Select (SS) pin is always input. When SS is
held low, the SPI is activated, and MISO becomes an output if configured so by the user. All
other pins are inputs. When SS is driven high, all pins are inputs, and the SPI is passive, which
means that it will not receive incoming data. Note that the SPI logic will be reset once the SS pin
is driven high.
The SS pin is useful for packet/byte synchronization to keep the slave bit counter synchronous
with the master clock generator. When the SS pin is driven high, the SPI slave will immediately
reset the send and receive logic, and drop any partially received data in the Shift Register.
18.3.2 Master Mode
When the SPI is configured as a Master (MSTR in SPCR is set), the user can determine the
direction of the SS pin.
If SS is configured as an output, the pin is a general output pin which does not affect the SPI
system. Typically, the pin will be driving the SS pin of the SPI Slave.
If SS is configured as an input, it must be held high to ensure Master SPI operation. If the SS pin
is driven low by peripheral circuitry when the SPI is configured as a Master with the SS pin
defined as an input, the SPI system interprets this as another master selecting the SPI as a
slave and starting to send data to it. To avoid bus contention, the SPI system takes the following
actions:
1. The MSTR bit in SPCR is cleared and the SPI system becomes a Slave. As a result of
the SPI becoming a Slave, the MOSI and SCK pins become inputs.
2. The SPIF Flag in SPSR is set, and if the SPI interrupt is enabled, and the I-bit in SREG is
set, the interrupt routine will be executed.
Thus, when interrupt-driven SPI transmission is used in Master mode, and there exists a possi-
bility that SS is driven low, the interrupt should always check that the MSTR bit is still set. If the
MSTR bit has been cleared by a slave select, it must be set by the user to re-enable SPI Master
mode.
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18.4 Data Modes
There are four combinations of SCK phase and polarity with respect to serial data, which are
determined by control bits CPHA and CPOL. The SPI data transfer formats are shown in Figure
18-3 and Figure 18-4. Data bits are shifted out and latched in on opposite edges of the SCK sig-
nal, ensuring sufficient time for data signals to stabilize. This is clearly seen by summarizing
Table 18-3 and Table 18-4, as done below:
Figure 18-3. SPI Transfer Format with CPHA = 0
Table 18-2. CPOL Functionality
Leading Edge Trailing eDge SPI Mode
CPOL=0, CPHA=0 Sample (Rising) Setup (Falling) 0
CPOL=0, CPHA=1 Setup (Rising) Sample (Falling) 1
CPOL=1, CPHA=0 Sample (Falling) Setup (Rising) 2
CPOL=1, CPHA=1 Setup (Falling) Sample (Rising) 3
Bit 1
Bit 6
LSB
MSB
SCK (CPOL = 0)
mode 0
SAMPLE I
MOSI/MISO
CHANGE 0
MOSI PIN
CHANGE 0
MISO PIN
SCK (CPOL = 1)
mode 2
SS
MSB
LSB
Bit 6
Bit 1
Bit 5
Bit 2
Bit 4
Bit 3
Bit 3
Bit 4
Bit 2
Bit 5
MSB first (DORD = 0)
LSB first (DORD = 1)
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Figure 18-4. SPI Transfer Format with CPHA = 1
18.5 Register Description
18.5.1 SPCR – SPI Control Register
• Bit 7 – SPIE: SPI Interrupt Enable
This bit causes the SPI interrupt to be executed if SPIF bit in the SPSR Register is set and the if
the Global Interrupt Enable bit in SREG is set.
• Bit 6 – SPE: SPI Enable
When the SPE bit is written to one, the SPI is enabled. This bit must be set to enable any SPI
operations.
• Bit 5 – DORD: Data Order
When the DORD bit is written to one, the LSB of the data word is transmitted first.
When the DORD bit is written to zero, the MSB of the data word is transmitted first.
• Bit 4 – MSTR: Master/Slave Select
This bit selects Master SPI mode when written to one, and Slave SPI mode when written logic
zero. If SS is configured as an input and is driven low while MSTR is set, MSTR will be cleared,
and SPIF in SPSR will become set. The user will then have to set MSTR to re-enable SPI Mas-
ter mode.
SCK (CPOL = 0)
mode 1
SAMPLE I
MOSI/MISO
CHANGE 0
MOSI PIN
CHANGE 0
MISO PIN
SCK (CPOL = 1)
mode 3
SS
MSB
LSB
Bit 6
Bit 1
Bit 5
Bit 2
Bit 4
Bit 3
Bit 3
Bit 4
Bit 2
Bit 5
Bit 1
Bit 6
LSB
MSB
MSB first (DORD = 0)
LSB first (DORD = 1)
Bit 76543210
0x2C (0x4C) SPIE SPE DORD MSTR CPOL CPHA SPR1 SPR0 SPCR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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• Bit 3 – CPOL: Clock Polarity
When this bit is written to one, SCK is high when idle. When CPOL is written to zero, SCK is low
when idle. Refer to Figure 18-3 and Figure 18-4 for an example. The CPOL functionality is sum-
marized below:
• Bit 2 – CPHA: Clock Phase
The settings of the Clock Phase bit (CPHA) determine if data is sampled on the leading (first) or
trailing (last) edge of SCK. Refer to Figure 18-3 and Figure 18-4 for an example. The CPOL
functionality is summarized below:
• Bits 1, 0 – SPR1, SPR0: SPI Clock Rate Select 1 and 0
These two bits control the SCK rate of the device configured as a Master. SPR1 and SPR0 have
no effect on the Slave. The relationship between SCK and the Oscillator Clock frequency fosc is
shown in the following table:
Table 18-3. CPOL Functionality
CPOL Leading Edge Trailing Edge
0 Rising Falling
1 Falling Rising
Table 18-4. CPHA Functionality
CPHA Leading Edge Trailing Edge
0 Sample Setup
1 Setup Sample
Table 18-5. Relationship Between SCK and the Oscillator Frequency
SPI2X SPR1 SPR0 SCK Frequency
000
fosc/4
001
fosc/16
010
fosc/64
011
fosc/128
100
fosc/2
101
fosc/8
110
fosc/32
111
fosc/64
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18.5.2 SPSR – SPI Status Register
• Bit 7 – SPIF: SPI Interrupt Flag
When a serial transfer is complete, the SPIF Flag is set. An interrupt is generated if SPIE in
SPCR is set and global interrupts are enabled. If SS is an input and is driven low when the SPI is
in Master mode, this will also set the SPIF Flag. SPIF is cleared by hardware when executing the
corresponding interrupt handling vector. Alternatively, the SPIF bit is cleared by first reading the
SPI Status Register with SPIF set, then accessing the SPI Data Register (SPDR).
• Bit 6 – WCOL: Write COLlision Flag
The WCOL bit is set if the SPI Data Register (SPDR) is written during a data transfer. The
WCOL bit (and the SPIF bit) are cleared by first reading the SPI Status Register with WCOL set,
and then accessing the SPI Data Register.
• Bit 5..1 – Reserved Bits
These bits are reserved bits in the ATmega329/3290/649/6490 and will always read as zero.
• Bit 0 – SPI2X: Double SPI Speed Bit
When this bit is written logic one the SPI speed (SCK Frequency) will be doubled when the SPI
is in Master mode (see Table 18-5). This means that the minimum SCK period will be two CPU
clock periods. When the SPI is configured as Slave, the SPI is only guaranteed to work at fosc/4
or lower.
The SPI interface on the ATmega329/3290/649/6490 is also used for program memory and
EEPROM downloading or uploading. See page 308 for serial programming and verification.
18.5.3 SPDR – SPI Data Register
The SPI Data Register is a read/write register used for data transfer between the Register File
and the SPI Shift Register. Writing to the register initiates data transmission. Reading the regis-
ter causes the Shift Register Receive buffer to be read.
Bit 76543210
0x2D (0x4D) SPIFWCOL–––––SPI2XSPSR
Read/WriteRRRRRRRR/W
Initial Value00000000
Bit 76543210
0x2E (0x4E) MSB LSB SPDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value X X X X X X X X Undefined
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19. USART0
19.1 Features
The Universal Synchronous and Asynchronous serial Receiver and Transmitter (USART) is a
highly flexible serial communication device. The main features are:
•Full Duplex Operation (Independent Serial Receive and Transmit Registers)
•Asynchronous or Synchronous Operation
•Master or Slave Clocked Synchronous Operation
•High Resolution Baud Rate Generator
•Supports Serial Frames with 5, 6, 7, 8, or 9 Data Bits and 1 or 2 Stop Bits
•Odd or Even Parity Generation and Parity Check Supported by Hardware
•Data OverRun Detection
•Framing Error Detection
•Noise Filtering Includes False Start Bit Detection and Digital Low Pass Filter
•Three Separate Interrupts on TX Complete, TX Data Register Empty and RX Complete
•Multi-processor Communication Mode
•Double Speed Asynchronous Communication Mode
19.2 Overview
A simplified block diagram of the USART Transmitter is shown in Figure 19-1. CPU accessible
I/O Registers and I/O pins are shown in bold.
The Power Reduction USART bit, PRUSART0, in “PRR – Power Reduction Register” on page
40 must be written to zero to enable USART0 module.
Figure 19-1. USART Block Diagram(1)
Note: 1. Refer to Figure 1-1 on page 2, Figure 1-2 on page 3, “Alternate Functions of Port E” on page
75 for USART pin placement.
PARITY
GENERATOR
UBRR[H:L]
UDR (Transmit)
UCSRA UCSRB UCSRC
BAUD RATE GENERATOR
TRANSMIT SHIFT REGISTER
RECEIVE SHIFT REGISTER RxD
TxD
PIN
CONTROL
UDR (Receive)
PIN
CONTROL
XCK
DATA
RECOVERY
CLOCK
RECOVERY
PIN
CONTROL
TX
CONTROL
RX
CONTROL
PARITY
CHECKER
DATA BUS
OSC
SYNC LOGIC
Clock Generator
Transmitter
Receiver
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The dashed boxes in the block diagram separate the three main parts of the USART (listed from
the top): Clock Generator, Transmitter and Receiver. Control Registers are shared by all units.
The Clock Generation logic consists of synchronization logic for external clock input used by
synchronous slave operation, and the baud rate generator. The XCK (Transfer Clock) pin is only
used by synchronous transfer mode. The Transmitter consists of a single write buffer, a serial
Shift Register, Parity Generator and Control logic for handling different serial frame formats. The
write buffer allows a continuous transfer of data without any delay between frames. The
Receiver is the most complex part of the USART module due to its clock and data recovery
units. The recovery units are used for asynchronous data reception. In addition to the recovery
units, the Receiver includes a Parity Checker, Control logic, a Shift Register and a two level
receive buffer (UDRn). The Receiver supports the same frame formats as the Transmitter, and
can detect Frame Error, Data OverRun and Parity Errors.
19.2.1 AVR USART vs. AVR UART – Compatibility
The USART is fully compatible with the AVR UART regarding:
• Bit locations inside all USART Registers.
• Baud Rate Generation.
• Transmitter Operation.
• Transmit Buffer Functionality.
• Receiver Operation.
However, the receive buffering has two improvements that will affect the compatibility in some
special cases:
• A second Buffer Register has been added. The two Buffer Registers operate as a circular
FIFO buffer. Therefore the UDRn must only be read once for each incoming data! More
important is the fact that the Error Flags (FEn and DORn) and the ninth data bit (RXB8n) are
buffered with the data in the receive buffer. Therefore the status bits must always be read
before the UDRn Register is read. Otherwise the error status will be lost since the buffer
state is lost.
• The Receiver Shift Register can now act as a third buffer level. This is done by allowing the
received data to remain in the serial Shift Register (see Figure 19-1) if the Buffer Registers
are full, until a new start bit is detected. The USART is therefore more resistant to Data
OverRun (DORn) error conditions.
The following control bits have changed name, but have same functionality and register location:
• CHR9 is changed to UCSZn2.
• OR is changed to DORn.
19.3 Clock Generation
The Clock Generation logic generates the base clock for the Transmitter and Receiver. The
USART supports four modes of clock operation: Normal asynchronous, Double Speed asyn-
chronous, Master synchronous and Slave synchronous mode. The UMSELn bit in USART
Control and Status Register C (UCSRnC) selects between asynchronous and synchronous
operation. Double Speed (asynchronous mode only) is controlled by the U2Xn found in the
UCSRnA Register. When using synchronous mode (UMSELn = 1), the Data Direction Register
for the XCK pin (DDR_XCK) controls whether the clock source is internal (Master mode) or
external (Slave mode). The XCK pin is only active when using synchronous mode.
Figure 19-2 shows a block diagram of the clock generation logic.
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Figure 19-2. Clock Generation Logic, Block Diagram
Signal description:
txclk Transmitter clock (Internal Signal).
rxclk Receiver base clock (Internal Signal).
xcki Input from XCK pin (internal Signal). Used for synchronous slave
operation.
xcko Clock output to XCK pin (Internal Signal). Used for synchronous master
operation.
fosc XTAL pin frequency (System Clock).
19.3.1 Internal Clock Generation – The Baud Rate Generator
Internal clock generation is used for the asynchronous and the synchronous master modes of
operation. The description in this section refers to Figure 19-2.
The USART Baud Rate Register (UBRRn) and the down-counter connected to it function as a
programmable prescaler or baud rate generator. The down-counter, running at system clock
(fosc), is loaded with the UBRRn value each time the counter has counted down to zero or when
the UBRRnL Register is written. A clock is generated each time the counter reaches zero. This
clock is the baud rate generator clock output (= fosc/(UBRRn+1)). The Transmitter divides the
baud rate generator clock output by 2, 8 or 16 depending on mode. The baud rate generator out-
put is used directly by the Receiver’s clock and data recovery units. However, the recovery units
use a state machine that uses 2, 8 or 16 states depending on mode set by the state of the
UMSELn, U2Xn and DDR_XCK bits.
Table 19-1 contains equations for calculating the baud rate (in bits per second) and for calculat-
ing the UBRRn value for each mode of operation using an internally generated clock source.
Prescaling
Down-Counter /2
UBRR
/4 /2
fosc
UBRR+1
Sync
Register
OSC
XCK
Pin
txclk
U2X
UMSEL
DDR_XCK
0
1
0
1
xcki
xcko
DDR_XCK rxclk
0
1
1
0
Edge
Detector
UCPOL
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Note: 1. The baud rate is defined to be the transfer rate in bit per second (bps)
BAUD Baud rate (in bits per second, bps)
fOSC System Oscillator clock frequency
UBRRn Contents of the UBRRnH and UBRRnL Registers, (0-4095)
Some examples of UBRRn values for some system clock frequencies are found in Table 19-4
(see page 186).
19.3.2 Double Speed Operation (U2Xn)
The transfer rate can be doubled by setting the U2Xn bit in UCSRnA. Setting this bit only has
effect for the asynchronous operation. Set this bit to zero when using synchronous operation.
Setting this bit will reduce the divisor of the baud rate divider from 16 to 8, effectively doubling
the transfer rate for asynchronous communication. Note however that the Receiver will in this
case only use half the number of samples (reduced from 16 to 8) for data sampling and clock
recovery, and therefore a more accurate baud rate setting and system clock are required when
this mode is used. For the Transmitter, there are no downsides.
19.3.3 External Clock
External clocking is used by the synchronous slave modes of operation. The description in this
section refers to Figure 19-2 for details.
External clock input from the XCK pin is sampled by a synchronization register to minimize the
chance of meta-stability. The output from the synchronization register must then pass through
an edge detector before it can be used by the Transmitter and Receiver. This process intro-
duces a two CPU clock period delay and therefore the maximum external XCK clock frequency
is limited by the following equation:
Note that fosc depends on the stability of the system clock source. It is therefore recommended to
add some margin to avoid possible loss of data due to frequency variations.
Table 19-1. Equations for Calculating Baud Rate Register Setting
Operating Mode
Equation for Calculating
Baud Rate(1)
Equation for Calculating
UBRRn Value
Asynchronous Normal
mode (U2Xn = 0)
Asynchronous Double
Speed mode
(U2Xn = 1)
Synchronous Master
mode
BAUD fOSC
16 UBRR 1+()
---------------------------------------=
UBRR fOSC
16BAUD
------------------------1–=
BAUD fOSC
8UBRR 1+()
-----------------------------------=
UBRR fOSC
8BAUD
-------------------- 1–=
BAUD fOSC
2UBRR 1+()
-----------------------------------=
UBRR fOSC
2BAUD
-------------------- 1–=
fXCK
fOSC
4
-----------
<
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19.3.4 Synchronous Clock Operation
When synchronous mode is used (UMSELn = 1), the XCK pin will be used as either clock input
(Slave) or clock output (Master). The dependency between the clock edges and data sampling
or data change is the same. The basic principle is that data input (on RxD) is sampled at the
opposite XCK clock edge of the edge the data output (TxD) is changed.
Figure 19-3. Synchronous Mode XCK Timing.
The UCPOLn bit UCRSC selects which XCK clock edge is used for data sampling and which is
used for data change. As Figure 19-3 shows, when UCPOLn is zero the data will be changed at
rising XCK edge and sampled at falling XCK edge. If UCPOLn is set, the data will be changed at
falling XCK edge and sampled at rising XCK edge.
19.4 Frame Formats
A serial frame is defined to be one character of data bits with synchronization bits (start and stop
bits), and optionally a parity bit for error checking. The USART accepts all 30 combinations of
the following as valid frame formats:
• 1 start bit
•5, 6, 7, 8, or 9 data bits
• no, even or odd parity bit
• 1 or 2 stop bits
A frame starts with the start bit followed by the least significant data bit. Then the next data bits,
up to a total of nine, are succeeding, ending with the most significant bit. If enabled, the parity bit
is inserted after the data bits, before the stop bits. When a complete frame is transmitted, it can
be directly followed by a new frame, or the communication line can be set to an idle (high) state.
Figure 19-4 illustrates the possible combinations of the frame formats. Bits inside brackets are
optional.
RxD / TxD
XCK
RxD / TxD
XCK
UCPOL = 0
UCPOL = 1
Sample
Sample
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Figure 19-4. Frame Formats
St Start bit, always low.
(n) Data bits (0 to 8).
PParity bit. Can be odd or even.
Sp Stop bit, always high.
IDLE No transfers on the communication line (RxD or TxD). An IDLE line must
be
high.
The frame format used by the USART is set by the UCSZn2:0, UPMn1:0 and USBSn bits in
UCSRnB and UCSRnC. The Receiver and Transmitter use the same setting. Note that changing
the setting of any of these bits will corrupt all ongoing communication for both the Receiver and
Transmitter.
The USART Character SiZe (UCSZn2:0) bits select the number of data bits in the frame. The
USART Parity mode (UPMn1:0) bits enable and set the type of parity bit. The selection between
one or two stop bits is done by the USART Stop Bit Select (USBSn) bit. The Receiver ignores
the second stop bit. An FEn (Frame Error) will therefore only be detected in the cases where the
first stop bit is zero.
19.4.1 Parity Bit Calculation
The parity bit is calculated by doing an exclusive-or of all the data bits. If odd parity is used, the
result of the exclusive or is inverted. The relation between the parity bit and data bits is as
follows:
Peven Parity bit using even parity
Podd Parity bit using odd parity
dnData bit n of the character
If used, the parity bit is located between the last data bit and first stop bit of a serial frame.
19.5 USART Initialization
The USART has to be initialized before any communication can take place. The initialization pro-
cess normally consists of setting the baud rate, setting frame format and enabling the
Transmitter or the Receiver depending on the usage. For interrupt driven USART operation, the
Global Interrupt Flag should be cleared (and interrupts globally disabled) when doing the
initialization.
10 2 3 4 [5] [6] [7] [8] [P]St Sp1 [Sp2] (St / IDLE)(IDLE)
FRAME
Peven dn1–…d3d2d1d00
Podd
⊕⊕⊕⊕⊕⊕
dn1–…d3d2d1d01⊕⊕⊕⊕⊕⊕
=
=
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Before doing a re-initialization with changed baud rate or frame format, be sure that there are no
ongoing transmissions during the period the registers are changed. The TXCn Flag can be used
to check that the Transmitter has completed all transfers, and the RXCn Flag can be used to
check that there are no unread data in the receive buffer. Note that the TXCn Flag must be
cleared before each transmission (before UDRn is written) if it is used for this purpose.
The following simple USART initialization code examples show one assembly and one C func-
tion that are equal in functionality. The examples assume asynchronous operation using polling
(no interrupts enabled) and a fixed frame format. The baud rate is given as a function parameter.
For the assembly code, the baud rate parameter is assumed to be stored in the r17:r16
Registers.
Note: 1. See “About Code Examples” on page 9.
Assembly Code Example(1)
USART_Init:
; Set baud rate
out UBRR0H, r17
out UBRR0L, r16
; Enable receiver and transmitter
ldi r16, (1<<RXEN0)|(1<<TXEN0)
out UCSR0B,r16
; Set frame format: 8data, 2stop bit
ldi r16, (1<<USBS0)|(3<<UCSZ00)
out UCSR0C,r16
ret
C Code Example(1)
#define FOSC 1843200 // Clock Speed
#define BAUD 9600
#define MYUBRR FOSC/16/BAUD-1
void main( void )
{
...
USART_Init(MYUBRR)
...
}
void USART_Init( unsigned int ubrr)
{
/* Set baud rate */
UBRR0H = (unsigned char)(ubrr>>8);
UBRR0L = (unsigned char)ubrr;
/* Enable receiver and transmitter */
UCSR0B = (1<<RXEN0)|(1<<TXEN0);
/* Set frame format: 8data, 2stop bit */
UCSR0C = (1<<USBS0)|(3<<UCSZ00);
}
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More advanced initialization routines can be made that include frame format as parameters, dis-
able interrupts and so on. However, many applications use a fixed setting of the baud and
control registers, and for these types of applications the initialization code can be placed directly
in the main routine, or be combined with initialization code for other I/O modules.
19.6 Data Transmission – The USART Transmitter
The USART Transmitter is enabled by setting the Transmit Enable (TXENn) bit in the UCSRnB
Register. When the Transmitter is enabled, the normal port operation of the TxD pin is overrid-
den by the USART and given the function as the Transmitter’s serial output. The baud rate,
mode of operation and frame format must be set up once before doing any transmissions. If syn-
chronous operation is used, the clock on the XCK pin will be overridden and used as
transmission clock.
19.6.1 Sending Frames with 5 to 8 Data Bit
A data transmission is initiated by loading the transmit buffer with the data to be transmitted. The
CPU can load the transmit buffer by writing to the UDRn I/O location. The buffered data in the
transmit buffer will be moved to the Shift Register when the Shift Register is ready to send a new
frame. The Shift Register is loaded with new data if it is in idle state (no ongoing transmission) or
immediately after the last stop bit of the previous frame is transmitted. When the Shift Register is
loaded with new data, it will transfer one complete frame at the rate given by the Baud Register,
U2Xn bit or by XCK depending on mode of operation.
The following code examples show a simple USART transmit function based on polling of the
Data Register Empty (UDREn) Flag. When using frames with less than eight bits, the most sig-
nificant bits written to the UDRn are ignored. The USART has to be initialized before the function
can be used. For the assembly code, the data to be sent is assumed to be stored in Register
R16.
Note: 1. See “About Code Examples” on page 9.
Assembly Code Example(1)
USART_Transmit:
; Wait for empty transmit buffer
sbis UCSR0A,UDRE0
rjmp USART_Transmit
; Put data (r16) into buffer, sends the data
out UDR0,r16
ret
C Code Example(1)
void USART_Transmit( unsigned char data )
{
/* Wait for empty transmit buffer */
while ( !( UCSR0A & (1<<UDRE0)) )
;
/* Put data into buffer, sends the data */
UDR0 = data;
}
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The function simply waits for the transmit buffer to be empty by checking the UDREn Flag,
before loading it with new data to be transmitted. If the Data Register Empty interrupt is utilized,
the interrupt routine writes the data into the buffer.
19.6.2 Sending Frames with 9 Data Bit
If 9-bit characters are used (UCSZ = 7), the ninth bit must be written to the TXB8n bit in
UCSRnB before the low byte of the character is written to UDRn. The following code examples
show a transmit function that handles 9-bit characters. For the assembly code, the data to be
sent is assumed to be stored in registers R17:R16.
Notes: 1. These transmit functions are written to be general functions. They can be optimized if the con-
tents of the UCSRnB is static. For example, only the TXB80 bit of the UCSRnB Register is
used after initialization.
2. See “About Code Examples” on page 9.
The ninth bit can be used for indicating an address frame when using multi processor communi-
cation mode or for other protocol handling as for example synchronization.
Assembly Code Example(1)(2)
USART_Transmit:
; Wait for empty transmit buffer
sbis UCSR0A,UDRE0
rjmp USART_Transmit
; Copy 9th bit from r17 to TXB80
cbi UCSR0B,TXB80
sbrc r17,0
sbi UCSR0B,TXB80
; Put LSB data (r16) into buffer, sends the data
out UDR0,r16
ret
C Code Example(1)(2)
void USART_Transmit( unsigned int data )
{
/* Wait for empty transmit buffer */
while ( !( UCSR0A & (1<<UDRE0))) )
;
/* Copy 9th bit to TXB80 */
UCSR0B &= ~(1<<TXB80);
if ( data & 0x0100 )
UCSR0B |= (1<<TXB80);
/* Put data into buffer, sends the data */
UDR0 = data;
}
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19.6.3 Transmitter Flags and Interrupts
The USART Transmitter has two flags that indicate its state: USART Data Register Empty
(UDREn) and Transmit Complete (TXCn). Both flags can be used for generating interrupts.
The Data Register Empty (UDREn) Flag indicates whether the transmit buffer is ready to receive
new data. This bit is set when the transmit buffer is empty, and cleared when the transmit buffer
contains data to be transmitted that has not yet been moved into the Shift Register. For compat-
ibility with future devices, always write this bit to zero when writing the UCSRnA Register.
When the Data Register Empty Interrupt Enable (UDRIEn) bit in UCSRnB is written to one, the
USART Data Register Empty Interrupt will be executed as long as UDREn is set (provided that
global interrupts are enabled). UDREn is cleared by writing UDRn. When interrupt-driven data
transmission is used, the Data Register Empty interrupt routine must either write new data to
UDRn in order to clear UDREn or disable the Data Register Empty interrupt, otherwise a new
interrupt will occur once the interrupt routine terminates.
The Transmit Complete (TXCn) Flag bit is set one when the entire frame in the Transmit Shift
Register has been shifted out and there are no new data currently present in the transmit buffer.
The TXCn Flag bit is automatically cleared when a transmit complete interrupt is executed, or it
can be cleared by writing a one to its bit location. The TXCn Flag is useful in half-duplex commu-
nication interfaces (like the RS-485 standard), where a transmitting application must enter
receive mode and free the communication bus immediately after completing the transmission.
When the Transmit Compete Interrupt Enable (TXCIEn) bit in UCSRnB is set, the USART
Transmit Complete Interrupt will be executed when the TXCn Flag becomes set (provided that
global interrupts are enabled). When the transmit complete interrupt is used, the interrupt han-
dling routine does not have to clear the TXCn Flag, this is done automatically when the interrupt
is executed.
19.6.4 Parity Generator
The Parity Generator calculates the parity bit for the serial frame data. When parity bit is enabled
(UPMn1 = 1), the transmitter control logic inserts the parity bit between the last data bit and the
first stop bit of the frame that is sent.
19.6.5 Disabling the Transmitter
The disabling of the Transmitter (setting the TXENn to zero) will not become effective until ongo-
ing and pending transmissions are completed, i.e., when the Transmit Shift Register and
Transmit Buffer Register do not contain data to be transmitted. When disabled, the Transmitter
will no longer override the TxD pin.
19.7 Data Reception – The USART Receiver
The USART Receiver is enabled by writing the Receive Enable (RXENn) bit in the UCSRnB
Register to one. When the Receiver is enabled, the normal pin operation of the RxD pin is over-
ridden by the USART and given the function as the Receiver’s serial input. The baud rate, mode
of operation and frame format must be set up once before any serial reception can be done. If
synchronous operation is used, the clock on the XCK pin will be used as transfer clock.
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19.7.1 Receiving Frames with 5 to 8 Data Bits
The Receiver starts data reception when it detects a valid start bit. Each bit that follows the start
bit will be sampled at the baud rate or XCK clock, and shifted into the Receive Shift Register until
the first stop bit of a frame is received. A second stop bit will be ignored by the Receiver. When
the first stop bit is received, i.e., a complete serial frame is present in the Receive Shift Register,
the contents of the Shift Register will be moved into the receive buffer. The receive buffer can
then be read by reading the UDRn I/O location.
The following code example shows a simple USART receive function based on polling of the
Receive Complete (RXCn) Flag. When using frames with less than eight bits the most significant
bits of the data read from the UDRn will be masked to zero. The USART has to be initialized
before the function can be used.
Note: 1. See “About Code Examples” on page 9.
The function simply waits for data to be present in the receive buffer by checking the RXCn Flag,
before reading the buffer and returning the value.
19.7.2 Receiving Frames with 9 Data Bits
If 9-bit characters are used (UCSZ=7) the ninth bit must be read from the RXB8n bit in UCSRnB
before reading the low bits from the UDRn. This rule applies to the FEn, DORn and UPEn Sta-
tus Flags as well. Read status from UCSRnA, then data from UDRn. Reading the UDRn I/O
location will change the state of the receive buffer FIFO and consequently the TXB8n, FEn,
DORn and UPEn bits, which all are stored in the FIFO, will change.
Assembly Code Example(1)
USART_Receive:
; Wait for data to be received
sbis UCSR0A, RXC0
rjmp USART_Receive
; Get and return received data from buffer
in r16, UDR0
ret
C Code Example(1)
unsigned char USART_Receive( void )
{
/* Wait for data to be received */
while ( !(UCSR0A & (1<<RXC0)) )
;
/* Get and return received data from buffer */
return UDR0;
}
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The following code example shows a simple USART receive function that handles both nine bit
characters and the status bits.
Note: 1. See “About Code Examples” on page 9.
The receive function example reads all the I/O Registers into the Register File before any com-
putation is done. This gives an optimal receive buffer utilization since the buffer location read will
be free to accept new data as early as possible.
Assembly Code Example(1)
USART_Receive:
; Wait for data to be received
sbis UCSR0A, RXC0
rjmp USART_Receive
; Get status and 9th bit, then data from buffer
in r18, UCSR0A
in r17, UCSR0B
in r16, UDRn
; If error, return -1
andi r18,(1<<FE0)|(1<<DOR0)|(1<<UPE0)
breq USART_ReceiveNoError
ldi r17, HIGH(-1)
ldi r16, LOW(-1)
USART_ReceiveNoError:
; Filter the 9th bit, then return
lsr r17
andi r17, 0x01
ret
C Code Example(1)
unsigned int USART_Receive( void )
{
unsigned char status, resh, resl;
/* Wait for data to be received */
while ( !(UCSR0A & (1<<RXC0)) )
;
/* Get status and 9th bit, then data */
/* from buffer */
status = UCSR0A;
resh = UCSR0B;
resl = UDRn;
/* If error, return -1 */
if ( status & (1<<FE0)|(1<<DOR0)|(1<<UPE0) )
return -1;
/* Filter the 9th bit, then return */
resh = (resh >> 1) & 0x01;
return ((resh << 8) | resl);
}
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19.7.3 Receive Compete Flag and Interrupt
The USART Receiver has one flag that indicates the Receiver state.
The Receive Complete (RXCn) Flag indicates if there are unread data present in the receive buf-
fer. This flag is one when unread data exist in the receive buffer, and zero when the receive
buffer is empty (i.e., does not contain any unread data). If the Receiver is disabled (RXENn = 0),
the receive buffer will be flushed and consequently the RXCn bit will become zero.
When the Receive Complete Interrupt Enable (RXCIEn) in UCSRnB is set, the USART Receive
Complete interrupt will be executed as long as the RXCn Flag is set (provided that global inter-
rupts are enabled). When interrupt-driven data reception is used, the receive complete routine
must read the received data from UDRn in order to clear the RXCn Flag, otherwise a new inter-
rupt will occur once the interrupt routine terminates.
19.7.4 Receiver Error Flags
The USART Receiver has three Error Flags: Frame Error (FEn), Data OverRun (DORn) and
Parity Error (UPEn). All can be accessed by reading UCSRnA. Common for the Error Flags is
that they are located in the receive buffer together with the frame for which they indicate the
error status. Due to the buffering of the Error Flags, the UCSRnA must be read before the
receive buffer (UDRn), since reading the UDRn I/O location changes the buffer read location.
Another equality for the Error Flags is that they can not be altered by software doing a write to
the flag location. However, all flags must be set to zero when the UCSRnA is written for upward
compatibility of future USART implementations. None of the Error Flags can generate interrupts.
The Frame Error (FEn) Flag indicates the state of the first stop bit of the next readable frame
stored in the receive buffer. The FEn Flag is zero when the stop bit was correctly read (as one),
and the FEn Flag will be one when the stop bit was incorrect (zero). This flag can be used for
detecting out-of-sync conditions, detecting break conditions and protocol handling. The FEn
Flag is not affected by the setting of the USBSn bit in UCSRnC since the Receiver ignores all,
except for the first, stop bits. For compatibility with future devices, always set this bit to zero
when writing to UCSRnA.
The Data OverRun (DORn) Flag indicates data loss due to a receiver buffer full condition. A
Data OverRun occurs when the receive buffer is full (two characters), it is a new character wait-
ing in the Receive Shift Register, and a new start bit is detected. If the DORn Flag is set there
was one or more serial frame lost between the frame last read from UDRn, and the next frame
read from UDRn. For compatibility with future devices, always write this bit to zero when writing
to UCSRnA. The DORn Flag is cleared when the frame received was successfully moved from
the Shift Register to the receive buffer.
The Parity Error (UPEn) Flag indicates that the next frame in the receive buffer had a Parity
Error when received. If Parity Check is not enabled the UPEn bit will always be read zero. For
compatibility with future devices, always set this bit to zero when writing to UCSRnA. For more
details see “Parity Bit Calculation” on page 173 and “Parity Checker” on page 180.
19.7.5 Parity Checker
The Parity Checker is active when the high USART Parity mode (UPMn1) bit is set. Type of Par-
ity Check to be performed (odd or even) is selected by the UPMn0 bit. When enabled, the Parity
Checker calculates the parity of the data bits in incoming frames and compares the result with
the parity bit from the serial frame. The result of the check is stored in the receive buffer together
with the received data and stop bits. The Parity Error (UPEn) Flag can then be read by software
to check if the frame had a Parity Error.
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The UPEn bit is set if the next character that can be read from the receive buffer had a Parity
Error when received and the Parity Checking was enabled at that point (UPMn1 = 1). This bit is
valid until the receive buffer (UDRn) is read.
19.7.6 Disabling the Receiver
In contrast to the Transmitter, disabling of the Receiver will be immediate. Data from ongoing
receptions will therefore be lost. When disabled (i.e., the RXENn is set to zero) the Receiver will
no longer override the normal function of the RxD port pin. The Receiver buffer FIFO will be
flushed when the Receiver is disabled. Remaining data in the buffer will be lost
19.7.7 Flushing the Receive Buffer
The receiver buffer FIFO will be flushed when the Receiver is disabled, i.e., the buffer will be
emptied of its contents. Unread data will be lost. If the buffer has to be flushed during normal
operation, due to for instance an error condition, read the UDRn I/O location until the RXCn Flag
is cleared. The following code example shows how to flush the receive buffer.
Note: 1. See “About Code Examples” on page 9.
19.8 Asynchronous Data Reception
The USART includes a clock recovery and a data recovery unit for handling asynchronous data
reception. The clock recovery logic is used for synchronizing the internally generated baud rate
clock to the incoming asynchronous serial frames at the RxD pin. The data recovery logic sam-
ples and low pass filters each incoming bit, thereby improving the noise immunity of the
Receiver. The asynchronous reception operational range depends on the accuracy of the inter-
nal baud rate clock, the rate of the incoming frames, and the frame size in number of bits.
19.8.1 Asynchronous Clock Recovery
The clock recovery logic synchronizes internal clock to the incoming serial frames. Figure 19-5
illustrates the sampling process of the start bit of an incoming frame. The sample rate is 16 times
the baud rate for Normal mode, and eight times the baud rate for Double Speed mode. The hor-
izontal arrows illustrate the synchronization variation due to the sampling process. Note the
larger time variation when using the Double Speed mode (U2Xn = 1) of operation. Samples
denoted zero are samples done when the RxD line is idle (i.e., no communication activity).
Assembly Code Example(1)
USART_Flush:
sbis UCSR0A, RXC0
ret
in r16, UDR0
rjmp USART_Flush
C Code Example(1)
void USART_Flush( void )
{
unsigned char dummy;
while ( UCSR0A & (1<<RXC0) ) dummy = UDR0;
}
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Figure 19-5. Start Bit Sampling
When the clock recovery logic detects a high (idle) to low (start) transition on the RxD line, the
start bit detection sequence is initiated. Let sample 1 denote the first zero-sample as shown in
the figure. The clock recovery logic then uses samples 8, 9, and 10 for Normal mode, and sam-
ples 4, 5, and 6 for Double Speed mode (indicated with sample numbers inside boxes on the
figure), to decide if a valid start bit is received. If two or more of these three samples have logical
high levels (the majority wins), the start bit is rejected as a noise spike and the Receiver starts
looking for the next high to low-transition. If however, a valid start bit is detected, the clock recov-
ery logic is synchronized and the data recovery can begin. The synchronization process is
repeated for each start bit.
19.8.2 Asynchronous Data Recovery
When the receiver clock is synchronized to the start bit, the data recovery can begin. The data
recovery unit uses a state machine that has 16 states for each bit in Normal mode and eight
states for each bit in Double Speed mode. Figure 19-6 shows the sampling of the data bits and
the parity bit. Each of the samples is given a number that is equal to the state of the recovery
unit.
Figure 19-6. Sampling of Data and Parity Bit
The decision of the logic level of the received bit is taken by doing a majority voting of the logic
value to the three samples in the center of the received bit. The center samples are emphasized
on the figure by having the sample number inside boxes. The majority voting process is done as
follows: If two or all three samples have high levels, the received bit is registered to be a logic 1.
If two or all three samples have low levels, the received bit is registered to be a logic 0. This
majority voting process acts as a low pass filter for the incoming signal on the RxD pin. The
recovery process is then repeated until a complete frame is received. Including the first stop bit.
Note that the Receiver only uses the first stop bit of a frame.
Figure 19-7 shows the sampling of the stop bit and the earliest possible beginning of the start bit
of the next frame.
12345678 9 10 11 12 13 14 15 16 12
STARTIDLE
00
BIT 0
3
1234 5 678120
RxD
Sample
(U2X = 0)
Sample
(U2X = 1)
12345678 9 10 11 12 13 14 15 16 1
BIT n
1234 5 6781
RxD
Sample
(U2X = 0)
Sample
(U2X = 1)
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Figure 19-7. Stop Bit Sampling and Next Start Bit Sampling
The same majority voting is done to the stop bit as done for the other bits in the frame. If the stop
bit is registered to have a logic 0 value, the Frame Error (FEn) Flag will be set.
A new high to low transition indicating the start bit of a new frame can come right after the last of
the bits used for majority voting. For Normal Speed mode, the first low level sample can be at
point marked (A) in Figure 19-7. For Double Speed mode the first low level must be delayed to
(B). (C) marks a stop bit of full length. The early start bit detection influences the operational
range of the Receiver.
19.8.3 Asynchronous Operational Range
The operational range of the Receiver is dependent on the mismatch between the received bit
rate and the internally generated baud rate. If the Transmitter is sending frames at too fast or too
slow bit rates, or the internally generated baud rate of the Receiver does not have a similar (see
Table 19-2) base frequency, the Receiver will not be able to synchronize the frames to the start
bit.
The following equations can be used to calculate the ratio of the incoming data rate and internal
receiver baud rate.
DSum of character size and parity size (D = 5 to 10 bit)
SSamples per bit. S = 16 for Normal Speed mode and S = 8 for Double Speed
mode.
SFFirst sample number used for majority voting. SF = 8 for normal speed and SF = 4
for Double Speed mode.
SMMiddle sample number used for majority voting. SM = 9 for normal speed and
SM= 5 for Double Speed mode.
Rslow is the ratio of the slowest incoming data rate that can be accepted in relation to the
receiver baud rate. Rfast is the ratio of the fastest incoming data rate that can be
accepted in relation to the receiver baud rate.
Table 19-2 and Table 19-3 list the maximum receiver baud rate error that can be tolerated. Note
that Normal Speed mode has higher toleration of baud rate variations.
12345678 9 10 0/1 0/1 0/1
STOP 1
1234 5 6 0/1
RxD
Sample
(U2X = 0)
Sample
(U2X = 1)
(A) (B) (C)
Rslow
D1+()S
S1–DS⋅SF
++
-------------------------------------------=
Rfast
D2+()S
D1+()SS
M
+
-----------------------------------=
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The recommendations of the maximum receiver baud rate error was made under the assump-
tion that the Receiver and Transmitter equally divides the maximum total error.
There are two possible sources for the receivers baud rate error. The Receiver’s system clock
(XTAL) will always have some minor instability over the supply voltage range and the tempera-
ture range. When using a crystal to generate the system clock, this is rarely a problem, but for a
resonator the system clock may differ more than 2% depending of the resonators tolerance. The
second source for the error is more controllable. The baud rate generator can not always do an
exact division of the system frequency to get the baud rate wanted. In this case an UBRRn value
that gives an acceptable low error can be used if possible.
Table 19-2. Recommended Maximum Receiver Baud Rate Error for Normal Speed Mode
(U2Xn = 0)
D
# (Data+Parity Bit) Rslow (%) Rfast (%) Max Total Error (%)
Recommended Max
Receiver Error (%)
5 93.20 106.67 +6.67/-6.8± 3.0
6 94.12 105.79 +5.79/-5.88 ± 2.5
794.81 105.11 +5.11/-5.19 ± 2.0
895.36 104.58+4.58/-4.54 ± 2.0
995.81 104.14 +4.14/-4.19 ± 1.5
10 96.17 103.78+3.78/-3.83± 1.5
Table 19-3. Recommended Maximum Receiver Baud Rate Error for Double Speed Mode
(U2Xn = 1)
D
# (Data+Parity Bit) Rslow (%) Rfast (%) Max Total Error (%)
Recommended Max
Receiver Error (%)
5 94.12 105.66 +5.66/-5.88 ± 2.5
6 94.92 104.92 +4.92/-5.08± 2.0
7 95.52 104,35 +4.35/-4.48± 1.5
896.00 103.90 +3.90/-4.00 ± 1.5
9 96.39 103.53 +3.53/-3.61 ± 1.5
10 96.70 103.23 +3.23/-3.30 ± 1.0
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19.9 Multi-processor Communication Mode
Setting the Multi-processor Communication mode (MPCMn) bit in UCSRnA enables a filtering
function of incoming frames received by the USART Receiver. Frames that do not contain
address information will be ignored and not put into the receive buffer. This effectively reduces
the number of incoming frames that has to be handled by the CPU, in a system with multiple
MCUs that communicate via the same serial bus. The Transmitter is unaffected by the MPCMn
setting, but has to be used differently when it is a part of a system utilizing the Multi-processor
Communication mode.
If the Receiver is set up to receive frames that contain 5 to 8 data bits, then the first stop bit indi-
cates if the frame contains data or address information. If the Receiver is set up for frames with
nine data bits, then the ninth bit (RXB8n) is used for identifying address and data frames. When
the frame type bit (the first stop or the ninth bit) is one, the frame contains an address. When the
frame type bit is zero the frame is a data frame.
The Multi-processor Communication mode enables several slave MCUs to receive data from a
master MCU. This is done by first decoding an address frame to find out which MCU has been
addressed. If a particular slave MCU has been addressed, it will receive the following data
frames as normal, while the other slave MCUs will ignore the received frames until another
address frame is received.
19.9.1 Using MPCM
For an MCU to act as a master MCU, it can use a 9-bit character frame format (UCSZ = 7). The
ninth bit (TXB8n) must be set when an address frame (TXB8n = 1) or cleared when a data frame
(TXB = 0) is being transmitted. The slave MCUs must in this case be set to use a 9-bit character
frame format.
The following procedure should be used to exchange data in Multi-processor Communication
mode:
1. All Slave MCUs are in Multi-processor Communication mode (MPCMn in UCSRnA is
set).
2. The Master MCU sends an address frame, and all slaves receive and read this frame. In
the Slave MCUs, the RXCn Flag in UCSRnA will be set as normal.
3. Each Slave MCU reads the UDRn Register and determines if it has been selected. If so,
it clears the MPCMn bit in UCSRnA, otherwise it waits for the next address byte and
keeps the MPCMn setting.
4. The addressed MCU will receive all data frames until a new address frame is received.
The other Slave MCUs, which still have the MPCMn bit set, will ignore the data frames.
5. When the last data frame is received by the addressed MCU, the addressed MCU sets
the MPCMn bit and waits for a new address frame from master. The process then
repeats from 2.
Using any of the 5- to 8-bit character frame formats is possible, but impractical since the
Receiver must change between using n and n+1 character frame formats. This makes full-
duplex operation difficult since the Transmitter and Receiver uses the same character size set-
ting. If 5- to 8-bit character frames are used, the Transmitter must be set to use two stop bit
(USBSn = 1) since the first stop bit is used for indicating the frame type.
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Do not use Read-Modify-Write instructions (SBI and CBI) to set or clear the MPCMn bit. The
MPCMn bit shares the same I/O location as the TXCn Flag and this might accidentally be
cleared when using SBI or CBI instructions.
19.10 Examples of Baud Rate Setting
For standard crystal and resonator frequencies, the most commonly used baud rates for asyn-
chronous operation can be generated by using the UBRRn settings in Table 19-4. UBRRn
values which yield an actual baud rate differing less than 0.5% from the target baud rate, are
bold in the table. Higher error ratings are acceptable, but the Receiver will have less noise resis-
tance when the error ratings are high, especially for large serial frames (see “Asynchronous
Operational Range” on page 183). The error values are calculated using the following equation:
Error[%] BaudRateClosest Match
BaudRate
-------------------------------------------------------- 1–
⎝⎠
⎛⎞
100%•=
Table 19-4. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies
Baud
Rate
(bps)
fosc = 1.0000MHz fosc = 1.8432MHz fosc = 2.0000MHz
U2Xn = 0 U2Xn = 1 U2Xn = 0 U2Xn = 1 U2Xn = 0 U2Xn = 1
UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error
2400 25 0.2% 51 0.2% 47 0.0% 95 0.0% 51 0.2% 103 0.2%
4800 12 0.2% 25 0.2% 23 0.0% 47 0.0% 25 0.2% 51 0.2%
9600 6 -7.0% 12 0.2% 11 0.0% 23 0.0% 12 0.2% 25 0.2%
14.4k 3 8.5% 8-3.5% 70.0%150.0%8-3.5% 16 2.1%
19.2k 2 8.5% 6 -7.0% 50.0%110.0%6 -7.0% 12 0.2%
28.8k18.5% 3 8.5% 3 0.0% 7 0.0% 38.5% 8-3.5%
38.4k 1 -18.6% 2 8.5% 2 0.0% 5 0.0% 28.5% 6 -7.0%
57.6k 0 8.5% 1 8.5% 1 0.0% 3 0.0% 18.5% 3 8.5%
76.8k––1-18.6% 1 -25.0% 20.0%1-18.6% 2 8.5%
115.2k – – 0 8.5% 0 0.0% 1 0.0% 08.5% 1 8.5%
230.4k––––––00.0%––––
250k––––––––––00.0%
Max. (1) 62.5kbps 125kbps 115.2kbps 230.4kbps 125kbps 250kbps
1. UBRR = 0, Error = 0.0%
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Table 19-5. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies (Continued)
Baud
Rate
(bps)
fosc = 3.6864MHz fosc = 4.0000MHz fosc = 7.3728MHz
U2Xn = 0U2Xn = 1U2Xn = 0U2Xn = 1U2Xn = 0U2Xn = 1
UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error
2400 95 0.0% 191 0.0% 103 0.2% 207 0.2% 191 0.0% 383 0.0%
4800 47 0.0% 95 0.0% 51 0.2% 103 0.2% 95 0.0% 191 0.0%
9600 23 0.0% 47 0.0% 25 0.2% 51 0.2% 47 0.0% 95 0.0%
14.4k 15 0.0% 31 0.0% 16 2.1% 34 -0.8%31 0.0% 63 0.0%
19.2k 11 0.0% 23 0.0% 12 0.2% 25 0.2% 23 0.0% 47 0.0%
28.8k70.0%150.0%8-3.5% 16 2.1% 15 0.0% 31 0.0%
38.4k 50.0%110.0%6 -7.0% 12 0.2% 11 0.0% 23 0.0%
57.6k 3 0.0% 7 0.0% 38.5% 8-3.5% 7 0.0% 15 0.0%
76.8k2 0.0% 5 0.0% 28.5% 6 -7.0% 5 0.0% 11 0.0%
115.2k 1 0.0% 3 0.0% 18.5% 3 8.5% 3 0.0% 7 0.0%
230.4k 0 0.0% 1 0.0% 08.5% 1 8.5% 1 0.0% 3 0.0%
250k 0 -7.8%1-7.8%0 0.0% 1 0.0% 1-7.8%3-7.8%
0.5M – – 0 -7.8%––00.0%0-7.8%1-7.8%
1M ––––––––––0-7.8%
Max. (1) 230.4kbps 460.8kbps 250kbps 0.5Mbps 460.8kbps 921.6kbps
1. UBRR = 0, Error = 0.0%
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Table 19-6. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies (Continued)
Baud
Rate
(bps)
fosc = 8.0000MHz fosc = 11.0592MHz fosc = 14.7456MHz
U2Xn = 0U2Xn = 1U2Xn = 0U2Xn = 1U2Xn = 0U2Xn = 1
UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error
2400 207 0.2% 416 -0.1% 287 0.0% 575 0.0% 383 0.0% 767 0.0%
4800 103 0.2% 207 0.2% 143 0.0% 287 0.0% 191 0.0% 383 0.0%
9600 51 0.2% 103 0.2% 71 0.0% 143 0.0% 95 0.0% 191 0.0%
14.4k 34 -0.8%680.6% 47 0.0% 95 0.0% 63 0.0% 127 0.0%
19.2k 25 0.2% 51 0.2% 35 0.0% 71 0.0% 47 0.0% 95 0.0%
28.8k162.1%34-0.8%23 0.0% 47 0.0% 31 0.0% 63 0.0%
38.4k 12 0.2% 25 0.2% 17 0.0% 35 0.0% 23 0.0% 47 0.0%
57.6k 8-3.5% 16 2.1% 11 0.0% 23 0.0% 15 0.0% 31 0.0%
76.8k6-7.0%12 0.2% 8 0.0% 17 0.0% 11 0.0% 23 0.0%
115.2k 3 8.5% 8-3.5% 5 0.0% 11 0.0% 7 0.0% 15 0.0%
230.4k 1 8.5% 3 8.5% 2 0.0% 5 0.0% 3 0.0% 7 0.0%
250k 1 0.0% 3 0.0% 2-7.8%5-7.8%3-7.8% 6 5.3%
0.5M 0 0.0% 1 0.0% ––2-7.8%1-7.8%3-7.8%
1M – – 00.0%––––0-7.8%1-7.8%
Max. (1) 0.5Mbps 1Mbps 691.2kbps 1.3824Mbps 921.6kbps 1.8432Mbps
1. UBRR = 0, Error = 0.0%
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Table 19-7. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies (Continued)
Baud
Rate
(bps)
fosc = 16.0000MHz fosc = 18.4320MHz fosc = 20.0000MHz
U2Xn = 0U2Xn = 1U2Xn = 0U2Xn = 1U2Xn = 0U2Xn = 1
UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error
2400 416 -0.1% 832 0.0% 479 0.0% 959 0.0% 520 0.0% 1041 0.0%
4800 207 0.2% 416 -0.1% 239 0.0% 479 0.0% 259 0.2% 520 0.0%
9600 103 0.2% 207 0.2% 119 0.0% 239 0.0% 129 0.2% 259 0.2%
14.4k 680.6% 138 -0.1% 79 0.0% 159 0.0% 86 -0.2% 173 -0.2%
19.2k 51 0.2% 103 0.2% 59 0.0% 119 0.0% 64 0.2% 129 0.2%
28.8k34-0.8%680.6% 39 0.0% 79 0.0% 42 0.9% 86 -0.2%
38.4k 25 0.2% 51 0.2% 29 0.0% 59 0.0% 32 -1.4% 64 0.2%
57.6k 16 2.1% 34 -0.8%19 0.0% 39 0.0% 21 -1.4% 42 0.9%
76.8k12 0.2% 25 0.2% 14 0.0% 29 0.0% 15 1.7% 32 -1.4%
115.2k 8-3.5% 16 2.1% 90.0%190.0%10 -1.4% 21 -1.4%
230.4k 3 8.5% 8-3.5% 4 0.0% 9 0.0% 48.5% 10 -1.4%
250k 3 0.0% 7 0.0% 4-7.8%82.4% 4 0.0% 9 0.0%
0.5M 1 0.0% 3 0.0% ––4-7.8% – – 4 0.0%
1M 0 0.0% 1 0.0% ––––––––
Max. (1) 1Mbps 2Mbps 1.152Mbps 2.304Mbps 1.25Mbps 2.5Mbps
1. UBRR = 0, Error = 0.0%
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19.11 Register Description
19.11.1 UDRn – USART I/O Data Register n
The USART Transmit Data Buffer Register and USART Receive Data Buffer Registers share the
same I/O address referred to as USART Data Register or UDRn. The Transmit Data Buffer Reg-
ister (TXB) will be the destination for data written to the UDRn Register location. Reading the
UDRn Register location will return the contents of the Receive Data Buffer Register (RXB).
For 5-, 6-, or 7-bit characters the upper unused bits will be ignored by the Transmitter and set to
zero by the Receiver.
The transmit buffer can only be written when the UDREn Flag in the UCSRnA Register is set.
Data written to UDRn when the UDREn Flag is not set, will be ignored by the USART Transmit-
ter. When data is written to the transmit buffer, and the Transmitter is enabled, the Transmitter
will load the data into the Transmit Shift Register when the Shift Register is empty. Then the
data will be serially transmitted on the TxD pin.
The receive buffer consists of a two level FIFO. The FIFO will change its state whenever the
receive buffer is accessed. Due to this behavior of the receive buffer, do not use Read-Modify-
Write instructions (SBI and CBI) on this location. Be careful when using bit test instructions
(SBIC and SBIS), since these also will change the state of the FIFO.
19.11.2 UCSRnA – USART Control and Status Register n A
• Bit 7 – RXCn: USART Receive Complete
This flag bit is set when there are unread data in the receive buffer and cleared when the receive
buffer is empty (i.e., does not contain any unread data). If the Receiver is disabled, the receive
buffer will be flushed and consequently the RXCn bit will become zero. The RXCn Flag can be
used to generate a Receive Complete interrupt (see description of the RXCIEn bit).
• Bit 6 – TXCn: USART Transmit Complete
This flag bit is set when the entire frame in the Transmit Shift Register has been shifted out and
there are no new data currently present in the transmit buffer (UDRn). The TXCn Flag bit is auto-
matically cleared when a transmit complete interrupt is executed, or it can be cleared by writing
a one to its bit location. The TXCn Flag can generate a Transmit Complete interrupt (see
description of the TXCIEn bit).
Bit 76543210
RXBn[7:0] UDRn (Read)
TXBn[7:0] UDRn (Write)
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
RXCn TXCn UDREn FEn DORn UPEn U2Xn MPCMn UCSRnA
Read/Write R R/W R R R R R/W R/W
Initial Value00100000
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• Bit 5 – UDREn: USART Data Register Empty
The UDREn Flag indicates if the transmit buffer (UDRn) is ready to receive new data. If UDREn
is one, the buffer is empty, and therefore ready to be written. The UDREn Flag can generate a
Data Register Empty interrupt (see description of the UDRIEn bit).
UDREn is set after a reset to indicate that the Transmitter is ready.
Bit 4 – FEn: Frame Error
This bit is set if the next character in the receive buffer had a Frame Error when received. I.e.,
when the first stop bit of the next character in the receive buffer is zero. This bit is valid until the
receive buffer (UDRn) is read. The FEn bit is zero when the stop bit of received data is one.
Always set this bit to zero when writing to UCSRnA.
• Bit 3 – DORn: Data OverRun
This bit is set if a Data OverRun condition is detected. A Data OverRun occurs when the receive
buffer is full (two characters), it is a new character waiting in the Receive Shift Register, and a
new start bit is detected. This bit is valid until the receive buffer (UDRn) is read. Always set this
bit to zero when writing to UCSRnA.
• Bit 2 – UPEn: USART Parity Error
This bit is set if the next character in the receive buffer had a Parity Error when received and the
Parity Checking was enabled at that point (UPMn1 = 1). This bit is valid until the receive buffer
(UDRn) is read. Always set this bit to zero when writing to UCSRnA.
• Bit 1 – U2Xn: Double the USART Transmission Speed
This bit only has effect for the asynchronous operation. Write this bit to zero when using syn-
chronous operation.
Writing this bit to one will reduce the divisor of the baud rate divider from 16 to 8 effectively dou-
bling the transfer rate for asynchronous communication.
• Bit 0 – MPCMn: Multi-processor Communication Mode
This bit enables the Multi-processor Communication mode. When the MPCMn bit is written to
one, all the incoming frames received by the USART Receiver that do not contain address infor-
mation will be ignored. The Transmitter is unaffected by the MPCMn setting. For more detailed
information see “Multi-processor Communication Mode” on page 185.
19.11.3 UCSRnB – USART Control and Status Register n B
• Bit 7 – RXCIEn: RX Complete Interrupt Enable
Writing this bit to one enables interrupt on the RXCn Flag. A USART Receive Complete interrupt
will be generated only if the RXCIEn bit is written to one, the Global Interrupt Flag in SREG is
written to one and the RXCn bit in UCSRnA is set.
Bit 76543210
RXCIEn TXCIEn UDRIEn RXENn TXENn UCSZn2 RXB8n TXB8n UCSRnB
Read/Write R/W R/W R/W R/W R/W R/W R R/W
Initial Value 0 0 0 0 0 0 0 0
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• Bit 6 – TXCIEn: TX Complete Interrupt Enable
Writing this bit to one enables interrupt on the TXCn Flag. A USART Transmit Complete interrupt
will be generated only if the TXCIEn bit is written to one, the Global Interrupt Flag in SREG is
written to one and the TXCn bit in UCSRnA is set.
• Bit 5 – UDRIEn: USART Data Register Empty Interrupt Enable
Writing this bit to one enables interrupt on the UDREn Flag. A Data Register Empty interrupt will
be generated only if the UDRIEn bit is written to one, the Global Interrupt Flag in SREG is written
to one and the UDREn bit in UCSRnA is set.
• Bit 4 – RXEN0: Receiver Enable
Writing this bit to one enables the USART Receiver. The Receiver will override normal port oper-
ation for the RxD pin when enabled. Disabling the Receiver will flush the receive buffer
invalidating the FEn, DORn, and UPEn Flags.
• Bit 3 – TXENn: Transmitter Enable
Writing this bit to one enables the USART Transmitter. The Transmitter will override normal port
operation for the TxD pin when enabled. The disabling of the Transmitter (writing TXENn to
zero) will not become effective until ongoing and pending transmissions are completed, i.e.,
when the Transmit Shift Register and Transmit Buffer Register do not contain data to be trans-
mitted. When disabled, the Transmitter will no longer override the TxD port.
• Bit 2 – UCSZn2: Character Size
The UCSZn2 bits combined with the UCSZn1:0 bit in UCSRnC sets the number of data bits
(Character SiZe) in a frame the Receiver and Transmitter use.
• Bit 1 – RXB8n: Receive Data Bit 8
RXB8n is the ninth data bit of the received character when operating with serial frames with nine
data bits. Must be read before reading the low bits from UDRn.
• Bit 0 – TXB8n: Transmit Data Bit 8
TXB8n is the ninth data bit in the character to be transmitted when operating with serial frames
with nine data bits. Must be written before writing the low bits to UDRn.
19.11.4 UCSRnC – USART Control and Status Register n C
• Bit 6 – UMSELn: USART Mode Select
This bit selects between asynchronous and synchronous mode of operation.
Bit 7 6 543 2 1 0
– UMSELn UPMn1 UPMn0 USBSn UCSZn1 UCSZn0 UCPOLn UCSRnC
Read/Write R R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 1 1 0
Table 19-8. UMSELn Bit Settings
UMSELn Mode
0 Asynchronous Operation
1 Synchronous Operation
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• Bit 5:4 – UPMn1:0: Parity Mode
These bits enable and set type of parity generation and check. If enabled, the Transmitter will
automatically generate and send the parity of the transmitted data bits within each frame. The
Receiver will generate a parity value for the incoming data and compare it to the UPMn0 setting.
If a mismatch is detected, the UPEn Flag in UCSRnA will be set.
• Bit 3 – USBSn: Stop Bit Select
This bit selects the number of stop bits to be inserted by the Transmitter. The Receiver ignores
this setting.
• Bit 2:1 – UCSZn1:0: Character Size
The UCSZn1:0 bits combined with the UCSZn2 bit in UCSRnB sets the number of data bits
(Character SiZe) in a frame the Receiver and Transmitter use.
Table 19-9. UPMn Bits Settings
UPMn1 UPMn0 Parity Mode
0 0 Disabled
01Reserved
1 0 Enabled, Even Parity
1 1 Enabled, Odd Parity
Table 19-10. USBSn Bit Settings
USBSn Stop Bit(s)
01-bit
12-bit
Table 19-11. UCSZ Bits Settings
UCSZn2 UCSZn1 UCSZn0 Character Size
0 0 0 5-bit
0 0 1 6-bit
0 1 0 7-bit
0118-bit
100Reserved
101Reserved
110Reserved
1 1 1 9-bit
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• Bit 0 – UCPOLn: Clock Polarity
This bit is used for synchronous mode only. Write this bit to zero when asynchronous mode is
used. The UCPOLn bit sets the relationship between data output change and data input sample,
and the synchronous clock (XCK).
19.11.5 UBRRnL and UBRRnH – USART Baud Rate Registers n
• Bit 15:12 – Reserved Bits
These bits are reserved for future use. For compatibility with future devices, these bit must be
written to zero when UBRRnH is written.
• Bit 11:0 – UBRR11:0: USART Baud Rate Register
This is a 12-bit register which contains the USART baud rate. The UBRRnH contains the four
most significant bits, and the UBRRnL contains the eight least significant bits of the USART
baud rate. Ongoing transmissions by the Transmitter and Receiver will be corrupted if the baud
rate is changed. Writing UBRRnL will trigger an immediate update of the baud rate prescaler.
Table 19-12. UCPOLn Bit Settings
UCPOLn
Transmitted Data Changed
(Output of TxD Pin)
Received Data Sampled
(Input on RxD Pin)
0 Rising XCK Edge Falling XCK Edge
1 Falling XCK Edge Rising XCK Edge
Bit 151413121110 9 8
– – – – UBRRn[11:8] UBRRnH
UBRRn[7:0] UBRRnL
76543210
Read/WriteRRRRR/WR/WR/WR/W
R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
00000000
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20. USI – Universal Serial Interface
20.1 Features
The Universal Serial Interface, or 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. The main features of the USI are:
•Two-wire Synchronous Data Transfer (Master or Slave)
•Three-wire Synchronous Data Transfer (Master or Slave)
•Data Received Interrupt
•Wake up 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
20.2 Overview
A simplified block diagram of the USI is shown on Figure 20-1. For the actual placement of I/O
pins, refer to “Pinout ATmega3290/6490” on page 2 and “Pinout ATmega329/649” on page 3.
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 “Register Descriptions” on page 203.
Figure 20-1. 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.
DATA BUS
USIPF
USITC
USICLK
USICS0
USICS1
USIOIFUSIOIE
USIDC
USISIF
USIWM0
USIWM1
USISIE Bit7
Two-wire Clock
Control Unit
DO (Output only)
DI/SDA (Input/Open Drain)
USCK/SCL (Input/Open Drain)
4-bit Counter
USIDR
USISR
DQ
LE
USICR
CLOCK
HOLD
TIM0 COMP
Bit0
[1]
3
0
1
2
3
0
1
2
0
1
2
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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 con-
dition is detected, or after the counter overflows.
20.3 Functional Descriptions
20.3.1 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 20-2. Three-wire Mode Operation, Simplified Diagram
Figure 20-2 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.
SLAVE
MASTER
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
DO
DI
USCK
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
DO
DI
USCK
PORTxn
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Figure 20-3. Three-wire Mode, Timing Diagram
The Three-wire mode timing is shown in Figure 20-3. At the top of the figure is a USCK cycle ref-
erence. 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., sam-
ples 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 20-3.), a bus transfer involves the following steps:
1. The Slave device and Master device sets up its data output and, depending on the proto-
col used, enables its output 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 set-
ting 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.
MSB
MSB
654321LSB
1 2 3 4 5 6 7 8
654321LSB
USCK
USCK
DO
DI
DCBA E
CYCLE
( Reference )
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20.3.2 SPI Master Operation Example
The following code demonstrates how to use the USI module as a SPI Master:
SPITransfer:
sts USIDR,r16
ldi r16,(1<<USIOIF)
sts USISR,r16
ldi r16,(1<<USIWM0)|(1<<USICS1)|(1<<USICLK)|(1<<USITC)
SPITransfer_loop:
sts USICR,r16
lds r16, USISR
sbrs r16, USIOIF
rjmp SPITransfer_loop
lds 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 com-
pleted the data received from the Slave is stored back into the r16 Register.
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.
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The following code demonstrates how to use the USI module as a SPI Master with maximum
speed (fsck = fck/4):
SPITransfer_Fast:
sts USIDR,r16
ldi r16,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)
ldi r17,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)|(1<<USICLK)
sts USICR,r16 ; MSB
sts USICR,r17
sts USICR,r16
sts USICR,r17
sts USICR,r16
sts USICR,r17
sts USICR,r16
sts USICR,r17
sts USICR,r16
sts USICR,r17
sts USICR,r16
sts USICR,r17
sts USICR,r16
sts USICR,r17
sts USICR,r16 ; LSB
sts USICR,r17
lds r16,USIDR
ret
20.3.3 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)
sts USICR,r16
...
SlaveSPITransfer:
sts USIDR,r16
ldi r16,(1<<USIOIF)
sts USISR,r16
SlaveSPITransfer_loop:
lds r16, USISR
sbrs r16, USIOIF
rjmp SlaveSPITransfer_loop
lds r16,USIDR
ret
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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.
20.3.4 Two-wire Mode
The USI Two-wire mode is compliant to the Inter IC (TWI) bus protocol, but without slew rate lim-
iting on outputs and input noise filtering. Pin names used by this mode are SCL and SDA.
Figure 20-4. Two-wire Mode Operation, Simplified Diagram
Figure 20-4 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.
MASTER
SLAVE
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0 SDA
SCL
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
Two-wire Clock
Control Unit
HOLD
SCL
PORTxn
SDA
SCL
VCC
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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 20-5. Two-wire Mode, Typical Timing Diagram
Referring to the timing diagram (Figure 20-5.), 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 20-6.) 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 overflows 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 20-6. Start Condition Detector, Logic Diagram
PS ADDRESS
1 - 7 8 9
R/W ACK ACK
1 - 8 9
DATA ACK
1 - 8 9
DATA
SDA
SCL
A B D EC F
SDA
SCL
Write( USISIF)
CLOCK
HOLD
USISIF
DQ
CLR
DQ
CLR
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20.3.5 Start Condition Detector
The start condition detector is shown in Figure 20-6. 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 “Clock Systems and their Distribution” on page 26) must also be taken
into the consideration. Refer to the USISIF bit description on page 203 for further details.
20.3.6 Clock speed considerations.
Maximum frequency for SCL and SCK is fCK /4. This is also the maximum data transmit and
receieve rate in both two- and three-wire mode. In two-wire slave mode the Two-wire Clock Con-
trol 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.
20.4 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.
20.4.1 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.
20.4.2 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.
20.4.3 12-bit Timer/Counter
Combining the USI 4-bit counter and Timer/Counter0 allows them to be used as a 12-bit
counter.
20.4.4 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.
20.4.5 Software Interrupt
The counter overflow interrupt can be used as a software interrupt triggered by a clock strobe
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.
20.5 Register Descriptions
20.5.1 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 con-
trolled 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) dur-
ing 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.
20.5.2 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, the flag is set when the 4-
bit counter is incremented.
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 wake up 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 will only be cleared if a one is written to the USIOIF bit.
Clearing this bit will release the counter overflow hold of SCL in Two-wire mode.
Bit 7 6 5 4 3 2 1 0
(0xBA) 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
Bit 76543 210
(0xB9) 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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A counter overflow interrupt will wake up 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.
20.5.3 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 inter-
rupt when the USISIE and the Global Interrupt Enable Flag is set to one, this will immediately be
executed. Refer to the USISIF bit description on page 203 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.
Refer to the USIOIF bit description on page 203 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 exter-
nally, and data input sampled, even when outputs are disabled. The relations between
USIWM1..0 and the USI operation is summarized in Table 20-1.
Bit 7 6 5 4 3 2 1 0
(0xB8)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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Note: 1. The DI and USCK pins are renamed to Serial Data (SDA) and Serial Clock (SCL) respectively
to avoid confusion between the modes of operation.
• 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 20-1. 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.
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Table 20-2 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 exe-
cuted, 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 20-2).
• 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, writ-
ing 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 20-2. Relations between the USICS1..0 and USICLK Setting
USICS1 USICS0 USICLK
Shift Register Clock
Source
4-bit Counter Clock
Source
000No 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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21. Analog Comparator
21.1 Overview
The Analog Comparator compares the input values on the positive pin AIN0 and negative pin
AIN1. When the voltage on the positive pin AIN0 is higher than the voltage on the negative pin
AIN1, the Analog Comparator output, ACO, is set. The comparator’s output can be set to trigger
the Timer/Counter1 Input Capture function. In addition, the comparator can trigger a separate
interrupt, exclusive to the Analog Comparator. The user can select Interrupt triggering on com-
parator output rise, fall or toggle. A block diagram of the comparator and its surrounding logic is
shown in Figure 21-1.
The PRADC, in “Power Reduction Register - PRR” on page 35 must be written to zero to use the
ADC input MUX.
Figure 21-1. Analog Comparator Block Diagram(2)
Notes: 1. See Table 1 on page 208.
2. Refer to Figure 1-1 on page 2 and Table 13-5 on page 68 for Analog Comparator pin
placement.
ACBG
BANDGAP
REFERENCE
ADC MULTIPLEXER
OUTPUT
ACME
ADEN
(1)
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21.2 Analog Comparator Multiplexed Input
It is possible to select any of the ADC7..0 pins to replace the negative input to the Analog Com-
parator. The ADC multiplexer is used to select this input, and consequently, the ADC must be
switched off to utilize this feature. If the Analog Comparator Multiplexer Enable bit (ACME in
ADCSRB) is set and the ADC is switched off (ADEN in ADCSRA is zero), MUX2..0 in ADMUX
select the input pin to replace the negative input to the Analog Comparator, as shown in Table 1.
If ACME is cleared or ADEN is set, AIN1 is applied to the negative input to the Analog
Comparator.
Table 1. Analog Comparator Multiplexed Input
ACME ADEN MUX2..0 Analog Comparator Negative Input
0 x xxx AIN1
1 1 xxx AIN1
1 0 000 ADC0
1 0 001 ADC1
1 0 010 ADC2
1 0 011 ADC3
1 0 100 ADC4
1 0 101 ADC5
1 0 110 ADC6
1 0 111 ADC7
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21.3 Register Description
21.3.1 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 “Analog Comparator Multiplexed Input” on page 208.
21.3.2 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 Compar-
ator. When the bandgap reference is used as input to the analog comparator, it will take a
certain time for the voltage to stabilize. If not stabilized, the the first converison may give a wrong
value. See “Internal Voltage Reference” on page 44.
• 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 inter-
rupt handling vector. Alternatively, ACI is cleared by writing a logic one to the flag.
Bit 7 6543210
(0x7B) – ACME – – – ADTS2 ADTS1 ADTS0 ADCSRB
Read/Write R R/W R R R R/W R/W R/W
Initial Value00000000
Bit 76543210
0x30 (0x50) ACD ACBG ACO ACI ACIE ACIC ACIS1 ACIS0 ACSR
Read/Write R/W R/W R R/W R/W R/W R/W R/W
Initial Value 0 0 N/A00000
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• 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 Com-
parator 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 trig-
gered by the Analog Comparator. The comparator output is in this case directly connected to the
Input Capture front-end logic, making the comparator utilize the noise canceler and edge select
features of the Timer/Counter1 Input Capture interrupt. When written logic zero, no connection
between the Analog Comparator and the Input Capture function exists. To make the comparator
trigger the Timer/Counter1 Input Capture interrupt, the ICIE1 bit in the Timer Interrupt Mask
Register (TIMSK1) must be set.
• Bits 1, 0 – ACIS1, ACIS0: Analog Comparator Interrupt Mode Select
These bits determine which comparator events that trigger the Analog Comparator interrupt. The
different settings are shown in Table 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.
21.3.3 DIDR1 – Digital Input Disable Register 1
• Bit 1, 0 – AIN1D, AIN0D: AIN1, AIN0 Digital Input Disable
When this bit is written logic one, the digital input buffer on the AIN1/0 pin is disabled. The corre-
sponding 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 writ-
ten logic one to reduce power consumption in the digital input buffer.
Table 2. ACIS1/ACIS0 Settings
ACIS1 ACIS0 Interrupt Mode
0 0 Comparator Interrupt on Output Toggle.
01Reserved
1 0 Comparator Interrupt on Falling Output Edge.
1 1 Comparator Interrupt on Rising Output Edge.
Bit 76543210
(0x7F) –––––– AIN1D AIN0D DIDR1
Read/WriteRRRRRRR/WR/W
Initial Value00000000
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22. Analog to Digital Converter
22.1 Features
•10-bit Resolution
•0.5 LSB Integral Non-linearity
•± 2 LSB Absolute Accuracy
•13 - 260µs Conversion Time (50kHz to 1MHz ADC clock)
•Up to 76.9kSPS at Maximum Resolution (200kHz ADC clock)
•Eight Multiplexed Single Ended Input Channels
•Optional Left Adjustment for ADC Result Readout
•0 - VCC ADC Input Voltage Range
•Selectable 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
The ATmega329/3290/649/6490 features a 10-bit successive approximation ADC. The ADC is
connected to an 8-channel Analog Multiplexer which allows eight single-ended voltage inputs
constructed from the pins of Port F. The single-ended voltage inputs refer to 0V (GND).
The ADC contains a Sample and Hold circuit which ensures that the input voltage to the ADC is
held at a constant level during conversion. A block diagram of the ADC is shown in Figure 22-1.
The ADC has a separate analog supply voltage pin, AVCC. AVCC must not differ more than ±
0.3V from VCC. See the paragraph “ADC Noise Canceler” on page 217 on how to connect this
pin.
Internal reference voltages of nominally 1.1V or AVCC are provided On-chip. The voltage refer-
ence may be externally decoupled at the AREF pin by a capacitor for better noise performance.
The PRADC, in “Power Reduction Register - PRR” on page 35 must be written to zero to enable
the ADC module.
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Figure 22-1. Analog to Digital Converter Block Schematic
22.2 Operation
The ADC converts an analog input voltage to a 10-bit digital value through successive approxi-
mation. The minimum value represents GND and the maximum value represents the voltage on
the AREF pin minus 1 LSB. Optionally, AVCC or an internal 1.1V reference voltage may be con-
nected to the AREF pin by writing to the REFSn bits in the ADMUX Register. The internal
voltage reference may thus be decoupled by an external capacitor at the AREF pin to improve
noise immunity.
The analog input channel is selected by writing to the MUX bits in ADMUX. Any of the ADC input
pins, as well as GND and a fixed bandgap voltage reference, can be selected as single ended
inputs to the ADC. The ADC is enabled by setting the ADC Enable bit, ADEN in ADCSRA. Volt-
age 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 ADMUX.
ADC CONVERSION
COMPLETE IRQ
8-BIT DATA BUS
15 0
ADC MULTIPLEXER
SELECT (ADMUX) ADC CTRL. & STATUS
REGISTER (ADCSRA) ADC DATA REGISTER
(ADCH/ADCL)
MUX2
ADIE
ADATE
ADSC
ADEN
ADIF ADIF
MUX1
MUX0
ADPS0
ADPS1
ADPS2
MUX3
CONVERSION LOGIC
10-BIT DAC
+
-
SAMPLE & HOLD
COMPARATOR
INTERNAL
REFERENCE
MUX DECODER
MUX4
AVCC
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0
REFS0
REFS1
ADLAR
+
-
CHANNEL SELECTION
ADC[9:0]
ADC MULTIPLEXER
OUTPUT
DIFFERENTIAL
AMPLIFIER
AREF
BANDGAP
REFERENCE
PRESCALER
SINGLE ENDED / DIFFERENTIAL SELECTION
GND
POS.
INPUT
MUX
NEG.
INPUT
MUX
TRIGGER
SELECT
ADTS[2:0]
INTERRUPT
FLAGS
START
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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.
22.3 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 con-
versions 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 con-
version, 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 22-2. 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, con-
stantly 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.
ADSC
ADIF
SOURCE 1
SOURCE n
ADTS[2:0]
CONVERSION
LOGIC
PRESCALER
START CLKADC
.
.
.
.EDGE
DETECTOR
ADATE
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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.
22.4 Prescaling and Conversion Timing
Figure 22-3. 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.
When the bandgap reference voltage is used as input to the ADC, it will take a certain time for
the voltage to stabilize. If not stabilized the first value read after the first conversion may be
wrong.
The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conver-
sion and 13.5 ADC clock cycles after the start of an first conversion. When a conversion is
complete, the result is written to the ADC Data Registers, and ADIF is set. In Single Conversion
mode, ADSC is cleared simultaneously. The software may then set ADSC again, and a new
conversion will be initiated on the first rising ADC clock edge.
When Auto Triggering is used, the prescaler is reset when the trigger event occurs. This assures
a fixed delay from the trigger event to the start of conversion. In this mode, the sample-and-hold
takes place two ADC clock cycles after the rising edge on the trigger source signal. Three addi-
tional CPU clock cycles are used for synchronization logic. When using Differential mode, along
7-BIT ADC PRESCALER
ADC CLOCK SOURCE
CK
ADPS0
ADPS1
ADPS2
CK/128
CK/2
CK/4
CK/8
CK/16
CK/32
CK/64
Reset
ADEN
START
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with Auto triggering from a source other than the ADC Conversion Complete, each conversion
will require 25 ADC clocks. This is because the ADC must be disabled and re-enabled after
every conversion.
In Free Running mode, a new conversion will be started immediately after the conversion com-
pletes, while ADSC remains high. For a summary of conversion times, see Table 22-1.
Figure 22-4. ADC Timing Diagram, First Conversion (Single Conversion Mode)
Figure 22-5. ADC Timing Diagram, Single Conversion
Figure 22-6. ADC Timing Diagram, Auto Triggered Conversion
Sign and MSB of Result
LSB of Result
ADC Clock
ADSC
Sample & Hold
ADIF
ADCH
ADCL
Cycle Number
ADEN
1212
13 14 15 16 17 18 1920 21 22 23 24 25 1 2
First Conversion Next
Conversion
3
MUX and REFS
Update
MUX and REFS
Update
Conversion
Complete
12345678910 11 12 13
Sign and MSB of Result
LSB of Result
ADC Clock
ADSC
ADIF
ADCH
ADCL
Cycle Number 12
One Conversion Next Conversion
3
Sample & Hold
MUX and REFS
Update
Conversion
Complete MUX and REFS
Update
1 2 3 4 5 6 7 8 910 11 12 13
Sign and MSB of Result
LSB of Result
ADC Clock
Trigger
Source
ADIF
ADCH
ADCL
Cycle Number 12
One Conversion Next Conversion
Conversion
Complete
Prescaler
Reset
ADATE
Prescaler
Reset
Sample &
Hold
MUX and REFS
Update
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Figure 22-7. ADC Timing Diagram, Free Running Conversion
22.5 Changing Channel or Reference Selection
The MUXn and REFS1:0 bits in the ADMUX Register are single buffered through a temporary
register to which the CPU has random access. This ensures that the channels and reference
selection only takes place at a safe point during the conversion. The channel and reference
selection is continuously updated until a conversion is started. Once the conversion starts, the
channel and reference selection is locked to ensure a sufficient sampling time for the ADC. Con-
tinuous 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:
1. When ADATE or ADEN is cleared.
2. During conversion, minimum one ADC clock cycle after the trigger event.
3. 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.
Table 22-1. ADC Conversion Time
Condition
Sample & Hold (Cycles
from Start of Conversion)
Conversion Time
(Cycles)
First conversion 13.5 25
Normal conversions, single ended 1.5 13
Auto Triggered conversions 2 13.5
11 12 13
Sign and MSB of Result
LSB of Result
ADC Clock
ADSC
ADIF
ADCH
ADCL
Cycle Number 12
One Conversion Next Conversion
34
Conversion
Complete
Sample & Hold
MUX and REFS
Update
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22.5.1 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 chan-
nel 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 chan-
nel 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.
22.5.2 ADC Voltage Reference
The reference voltage for the ADC (VREF) indicates the conversion range for the ADC. Single
ended channels that exceed VREF will result in codes close to 0x3FF. VREF can be selected as
either AVCC, internal 1.1V reference, or external AREF pin.
AVCC is connected to the ADC through a passive switch. The internal 1.1V reference is gener-
ated from the internal bandgap reference (VBG) through an internal buffer. In either case, the
external AREF pin is directly connected to the ADC, and the reference voltage can be made
more immune to noise by connecting a capacitor between the AREF pin and ground. VREF can
also be measured at the AREF pin with a high impedant voltmeter. Note that VREF is a high
impedant source, and only a capacitive load should be connected in a system.
If the user has a fixed voltage source connected to the AREF pin, the user may not use the other
reference voltage options in the application, as they will be shorted to the external voltage. If no
external voltage is applied to the AREF pin, the user may switch between AVCC and 1.1V as
reference selection. The first ADC conversion result after switching reference voltage source
may be inaccurate, and the user is advised to discard this result.
22.5.3 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:
1. 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.
2. Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion
once the CPU has been halted.
3. 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 enter-
ing such sleep modes to avoid excessive power consumption.
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22.5.4 Analog Input Circuitry
The analog input circuitry for single ended channels is illustrated in Figure 22-8. An analog
source applied to ADCn is subjected to the pin capacitance and input leakage of that pin, regard-
less of whether that channel is selected as input for the ADC. When the channel is selected, the
source must drive the S/H capacitor through the series resistance (combined resistance in the
input path).
The ADC is optimized for analog signals with an output impedance of approximately 10 kΩ or
less. If such a source is used, the sampling time will be negligible. If a source with higher imped-
ance is used, the sampling time will depend on how long time the source needs to charge the
S/H capacitor, with can vary widely. The user is recommended to only use low impedant sources
with slowly varying signals, since this minimizes the required charge transfer to the S/H
capacitor.
Signal components higher than the Nyquist frequency (fADC/2) should not be present for either
kind of channels, to avoid distortion from unpredictable signal convolution. The user is advised
to remove high frequency components with a low-pass filter before applying the signals as
inputs to the ADC.
Figure 22-8. Analog Input Circuitry
22.5.5 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:
1. 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.
2. The AVCC pin on the device should be connected to the digital VCC supply voltage
via an LC network as shown in Figure 22-9.
3. Use the ADC noise canceler function to reduce induced noise from the CPU.
4. If any ADC port pins are used as digital outputs, it is essential that these do not
switch while a conversion is in progress.
ADCn
IIH
1..100 kΩ
CS/H= 14 pF
VCC/2
IIL
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Figure 22-9. ADC Power Connections
22.5.6 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 22-10. Offset Error
VCC
GND
100nF
Analog Ground Plane
(ADC0) PF0
(ADC7) PF7
(ADC1) PF1
(ADC2) PF2
(ADC3) PF3
(ADC4) PF4
(ADC5) PF5
(ADC6) PF6
AREF
GND
AVCC
52
53
54
55
56
57
58
59
60
6161
6262
6363
6464
1
51
LCDCAP
PA0
10μΗ
Output Code
V
REF
Input Voltage
Ideal ADC
Actual ADC
Offset
Error
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• 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 22-11. Gain Error
•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 22-12. Integral Non-linearity (INL)
Output Code
V
REF
Input Voltage
Ideal ADC
Actual ADC
Gain
Error
Output Code
VREF Input Voltage
Ideal ADC
Actual ADC
INL
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• 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 22-13. 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.
22.6 ADC Conversion Result
After the conversion is complete (ADIF is high), the conversion result can be found in the ADC
Result Registers (ADCL, ADCH).
For single ended conversion, the result is
where VIN is the voltage on the selected input pin and VREF the selected voltage reference (see
Table 22-3 on page 223 and Table 22-4 on page 224). 0x000 represents analog ground, and
0x3FF represents the selected reference voltage minus one LSB.
Output Code
0x3FF
0x000
0V
REF
Input Voltage
DNL
1 LSB
ADC VIN 1024⋅
VREF
--------------------------=
ADC VPOS VNEG
–()512⋅
VREF
-----------------------------------------------------=
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Figure 22-14. Differential Measurement Range
ADMUX = 0xFB (ADC3 - ADC2, 1.1V reference, left adjusted result)
Voltage on ADC3 is 300 mV, voltage on ADC2 is 500 mV.
ADCR = 512 * (300 - 500) / 1100 = -93 = 0x3A3.
ADCL will thus read 0xC0, and ADCH will read 0xD8. Writing zero to ADLAR right adjusts the
result: ADCL = 0xA3, ADCH = 0x03.
Table 22-2. Correlation Between Input Voltage and Output Codes
VADCn Read Code Corresponding Decimal Value
VADCm + VREF 0x1FF 511
VADCm + 511/512 VREF 0x1FF 511
VADCm + 510/512 VREF 0x1FE 510
... ... ...
VADCm + 1/512 VREF 0x001 1
VADCm 0x000 0
VADCm - 1/512 VREF 0x3FF -1
... ... ...
VADCm - 511/512 VREF 0x201 -511
VADCm - VREF 0x200 -512
0
Output Code
0x1FF
0x000
VREF Differential Input
Voltage (Volts)
0x3FF
0x200
- VREF
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22.7 Register Description
22.7.1 ADMUX – ADC Multiplexer Selection Register
• Bit 7:6 – REFS1:0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in Table 22-3. If these bits are
changed during a conversion, the change will not go in effect until this conversion is complete
(ADIF in ADCSRA is set). The internal voltage reference options may not be used if an external
reference voltage is being applied to the AREF pin.
• Bit 5 – ADLAR: ADC Left Adjust Result
The ADLAR bit affects the presentation of the ADC conversion result in the ADC Data Register.
Write one to ADLAR to left adjust the result. Otherwise, the result is right adjusted. Changing the
ADLAR bit will affect the ADC Data Register immediately, regardless of any ongoing conver-
sions. For a complete description of this bit, see “ADCL and ADCH – The ADC Data Register” on
page 226.
• Bits 4:0 – MUX4:0: Analog Channel Selection Bits
The value of these bits selects which combination of analog inputs are connected to the ADC.
See Table 22-4 for details. If these bits are changed during a conversion, the change will not go
in effect until this conversion is complete (ADIF in ADCSRA is set).
Bit 76543210
(0x7C) REFS1 REFS0 ADLAR 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 22-3. Voltage Reference Selections for ADC
REFS1 REFS0 Voltage Reference Selection
0 0 AREF, Internal Vref turned off
0 1 AVCC with external capacitor at AREF pin
10Reserved
1 1 Internal 1.1V Voltage Reference with external capacitor at AREF pin
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Table 22-4. Input Channel Selections
MUX4..0 Single Ended Input Positive Differential Input Negative Differential Input
00000 ADC0
N/A
00001 ADC1
00010 ADC2
00011 ADC3
00100 ADC4
00101 ADC5
00110 ADC6
00111 ADC7
01000
01001
01010
01011
01100
01101
01110
01111
10000 ADC0 ADC1
10001 ADC1 ADC1
10010 N/A ADC2 ADC1
10011 ADC3 ADC1
10100 ADC4 ADC1
10101 ADC5 ADC1
10110 ADC6 ADC1
10111 ADC7 ADC1
11000 ADC0 ADC2
11001 ADC1 ADC2
11010 ADC2 ADC2
11011 ADC3 ADC2
11100 ADC4 ADC2
11101 ADC5 ADC2
11110 1.1V (VBG)N/A
11111 0V (GND)
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22.7.2 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 initializa-
tion 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 con-
version 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. Alter-
natively, ADIF is cleared by writing a logical one to the flag. Beware that if doing a Read-Modify-
Write on ADCSRA, a pending interrupt can be disabled. This also applies if the SBI and CBI
instructions are used.
• 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 Inter-
rupt is activated.
Bit 76543210
(0x7A) 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 Value 0 0 0 0 0 0 0 0
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• Bits 2:0 – ADPS2:0: ADC Prescaler Select Bits
These bits determine the division factor between the XTAL frequency and the input clock to the
ADC.
22.7.3 ADCL and ADCH – The ADC Data Register
22.7.3.1 ADLAR = 0
22.7.3.2 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 ADMUX, and the MUXn bits in ADMUX affect the way the result is read from
the registers. If ADLAR is set, the result is left adjusted. If ADLAR is cleared (default), the result
is right adjusted.
Table 3. ADC Prescaler Selections
ADPS2 ADPS1 ADPS0 Division Factor
000 2
001 2
010 4
011 8
100 16
101 32
110 64
111 128
Bit 151413121110 9 8
(0x79) – – – – – – ADC9 ADC8 ADCH
(0x78)ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADC1 ADC0 ADCL
76543210
Read/WriteRRRRRRRR
RRRRRRRR
Initial Value00000000
00000000
Bit 151413121110 9 8
(0x79) ADC9 ADC8 ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADCH
(0x78)ADC1 ADC0 – –––––ADCL
76543210
Read/WriteRRRRRRRR
RRRRRRRR
Initial Value00000000
00000000
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• ADC9:0: ADC Conversion Result
These bits represent the result from the conversion, as detailed in “ADC Conversion Result” on
page 221.
22.7.4 ADCSRB – ADC Control and Status Register B
• Bit 7 – Reserved Bit
This bit is reserved for future use. To ensure compatibility with future devices, this bit must be
written to zero when ADCSRB is written.
• Bit 2:0 – ADTS2:0: ADC Auto Trigger Source
If ADATE in ADCSRA is written to one, the value of these bits selects which source will trigger
an ADC conversion. If ADATE is cleared, the ADTS2:0 settings will have no effect. A conversion
will be triggered by the rising edge of the selected Interrupt Flag. Note that switching from a trig-
ger 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.
22.7.5 DIDR0 – Digital Input Disable Register 0
• Bit 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 dis-
abled. 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.
Bit 76543210
(0x7B) –ACME – – – ADTS2 ADTS1 ADTS0 ADCSRB
Read/Write R R/W R R R R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 22-5. ADC Auto Trigger Source Selections
ADTS2 ADTS1 ADTS0 Trigger Source
0 0 0 Free Running mode
0 0 1 Analog Comparator
0 1 0 External Interrupt Request 0
0 1 1 Timer/Counter0 Compare MatchA
1 0 0 Timer/Counter0 Overflow
1 0 1 Timer/Counter1 Compare Match B
1 1 0 Timer/Counter1 Overflow
1 1 1 Timer/Counter1 Capture Event
Bit 76543210
(0x7E) 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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23. LCD Controller
The LCD Controller/driver is intended for monochrome passive liquid crystal display (LCD) with
up to four common terminals and up to 25/40 segment terminals.
23.1 Features
•Display Capacity of 25/40 Segments and Four Common Terminals
•Support Static, 1/2, 1/3 and 1/4 Duty
•Support Static, 1/2, 1/3 Bias
•On-chip LCD Power Supply, only One External Capacitor needed
•Display Possible in Power-save Mode for Low Power Consumption
•Software Selectable Low Power Waveform Capability
•Flexible Selection of Frame Frequency
•Software Selection between System Clock or an External Asynchronous Clock Source
•Equal Source and Sink Capability to maximize LCD Life Time
•LCD Interrupt Can be Used for Display Data Update or Wake-up from Sleep Mode
•Segment and Common Pins not Needed for Driving the Display Can be Used as Ordinary I/O Pins
•Latching of Display Data gives Full Freedom in Register Update
23.1.1 Overview
A simplified block diagram of the LCD Controller/Driver is shown in Figure 23-1. For the actual
placement of I/O pins, refer to “Pinout ATmega3290/6490” on page 2 and “Pinout
ATmega329/649” on page 3.
An LCD consists of several segments (pixels or complete symbols) which can be visible or non
visible. A segment has two electrodes with liquid crystal between them. When a voltage above a
threshold voltage is applied across the liquid crystal, the segment becomes visible.
The voltage must alternate to avoid an electrophoresis effect in the liquid crystal, which
degrades the display. Hence the waveform across a segment must not have a DC-component.
The PRLCD bit in “Power Reduction Register” on page 37 must be written to zero to enable the
LCD module.
23.1.2 Definitions
Several terms are used when describing LCD. The definitions in Table 23-1 are used throughout
this document.
Table 23-1. Definitions
LCD A passive display panel with terminals leading directly to a segment
Segment The least viewing element (pixel) which can be on or off
Common Denotes how many segments are connected to a segment terminal
Duty 1/(Number of common terminals on a actual LCD display)
Bias 1/(Number of voltage levels used driving a LCD display -1)
Frame Rate Number of times the LCD segments is energized per second.
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Figure 23-1. LCD Module Block Diagram
23.1.3 LCD Clock Sources
The LCD Controller can be clocked by an internal synchronous or an external asynchronous
clock source. The clock source clkLCD is by default equal to the system clock, clkI/O. When the
LCDCS bit in the LCDCRB Register is written to logic one, the clock source is taken from the
TOSC1 pin.
The clock source must be stable to obtain accurate LCD timing and hence minimize DC voltage
offset across LCD segments.
23.1.4 LCD Prescaler
The prescaler consist of a 12-bit ripple counter and a 1- to 8-clock divider. The LCDPS2:0 bits
selects clkLCD divided by 16, 64, 128, 256, 512, 1024, 2048, or 4096.
If a finer resolution rate is required, the LCDCD2:0 bits can be used to divide the clock further by
1 to 8.
Output from the clock divider clkLCD_PS is used as clock source for the LCD timing.
23.1.5 LCD Memory
The display memory is available through I/O Registers grouped for each common terminal.
When a bit in the display memory is written to one, the corresponding segment is energized (on),
and non-energized when a bit in the display memory is written to zero.
Clock
Multiplexer
12-bit Prescaler
0
1
Divide by 1 to 8
LCD
Timing
LCDCRB
LCDFRR
clk
i/o
TOSC
LCDCRA
D
A
T
A
B
U
S
clk
LCD
/4096
clk
LCD
/2048
clk
LCD
/128
clk
LCD
/1024
clk
LCD
/512
clk
LCD
/256
clk
LCD
/64
clk
LCD
/16
Analog
Switch
Array
lcdcs
lcdcd2:0
lcdps2:0
clk
LCD
SEG0
SEG1
SEG2
SEG3
SEG4
SEG5
SEG35
SEG36
SEG37
SEG38
SEG39
COM0
COM1
COM2
COM3
LCD Buffer/
Driver
V
LCD
LCDDR 19 -15
LCDDR 14 -10
LCDDR 9 - 5
LCDDR 4 - 0
LATCH
array
LCD Ouput
Decoder
LCDCCR
lcdcc3:0 Contrast Controller/
Power Supply
clk
LCD_PS
LCD
CAP
40 x
4:1
MUX
LCD_voltage_ok
1/3 V
LCD
1/2 V
LCD
2/3 V
LCD
LCD Display Configuration
lcddc2:0
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To energize a segment, an absolute voltage above a certain threshold must be applied. This is
done by letting the output voltage on corresponding COM pin and SEG pin have opposite phase.
For display with more than one common, one (1/2 bias) or two (1/3 bias) additional voltage lev-
els must be applied. Otherwise, non-energized segments on COM0 would be energized for all
non-selected common.
Addressing COM0 starts a frame by driving opposite phase with large amplitude out on COM0
compared to none addressed COM lines. Non-energized segments are in phase with the
addressed COM0, and energized segments have opposite phase and large amplitude. For
waveform figures refer to “Mode of Operation” on page 231. Latched data from LCDDR4 -
LCDDR0 is multiplexed into the decoder. The decoder is controlled from the LCD timing and
sets up signals controlling the analog switches to produce an output waveform. Next, COM1 is
addressed, and latched data from LCDDR9 - LCDDR5 is input to decoder. Addressing continu-
ous until all COM lines are addressed according to number of common (duty). The display data
are latched before a new frame start.
23.1.6 LCD Contrast Controller/Power Supply
The peak value (VLCD) on the output waveform determines the LCD Contrast. VLCD is controlled
by software from 2.6V to 3.35V independent of VCC. An internal signal inhibits output to the LCD
until VLCD has reached its target value.
23.1.7 LCDCAP
An external capacitor (typical > 470 nF) must be connected to the LCDCAP pin as shown in Fig-
ure 23-2. This capacitor acts as a reservoir for LCD power (VLCD). A large capacitance reduces
ripple on VLCD but increases the time until VLCD reaches its target value.
Figure 23-2. LCDCAP Connection
23.1.8 LCD Buffer Driver
Intermediate voltage levels are generated from buffers/drivers. The buffers are active the
amount of time specified by LCDDC[2:0] in LCDCCR. Then LCD output pins are tri-stated and
buffers are switched off. Shortening the drive time will reduce power consumption, but displays
with high internal resistance or capacitance may need longer drive time to achieve sufficient
contrast.
23.1.9 Display requirements
When using more than one common pin, the maximum period the LCD drivers can be turned on
for each voltage transition on the LCD pins is 50% of the prescaled LCD clock period, clkLCD_PS.
To avoid flickering, it is recommended to keep the framerate above 30Hz, thus giving a maxi-
mum drive time of approximately 2ms when using 1/2 or 1/4 duty, and approximately 2.7ms
321
64
63
62
LCDCAP
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when using 1/3 duty. To achieve satisfactory contrast, all segments on the LCD display must
therefore be able to be fully charged/discharged within 2 or 2.7ms, depending on the number of
common pins.
23.1.10 Minimizing power consumption
By keeping the percentage of the time the LCD drivers are turned on at a minimum, the power
consumption of the LCD driver can be minimized. This can be achieved by using the lowest
acceptable frame rate, and using low power waveform if possible. The drive time should be kept
at the lowest setting that achieves satisfactory contrast for a particular display, while allowing
some headroom for production variations between individual LCD drivers and displays. Note
that some of the highest LCD voltage settings may result in high power consumption when VCC
is below 2.0V. The recommended maximum LCD voltage is 2*(VCC - 0.2V).
23.2 Mode of Operation
23.2.1 Static Duty and Bias
If all segments on a LCD have one electrode common, then each segment must have a unique
terminal.
This kind of display is driven with the waveform shown in Figure 23-3. SEG0 - COM0 is the volt-
age across a segment that is on, and SEG1 - COM0 is the voltage across a segment that is off.
Figure 23-3. Driving a LCD with One Common Terminal
23.2.2 1/2 Duty and 1/2 Bias
For LCD with two common terminals (1/2 duty) a more complex waveform must be used to indi-
vidually control segments. Although 1/3 bias can be selected 1/2 bias is most common for these
displays. Waveform is shown in Figure 23-4. SEG0 - COM0 is the voltage across a segment that
is on, and SEG0 - COM1 is the voltage across a segment that is off.
VLCD
GND
VLCD
GND
VLCD
GND
-VLCD
SEG0
COM0
SEG0 - COM0
Frame Frame
VLCD
GND
VLCD
GND
GND
SEG1
COM0
SEG1 - COM0
Frame Frame
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Figure 23-4. Driving a LCD with Two Common Terminals
23.2.3 1/3 Duty and 1/3 Bias
1/3 bias is usually recommended for LCD with three common terminals (1/3 duty). Waveform is
shown in Figure 23-5. SEG0 - COM0 is the voltage across a segment that is on and SEG0-
COM1 is the voltage across a segment that is off.
Figure 23-5. Driving a LCD with Three Common Terminals
23.2.4 1/4 Duty and 1/3 Bias
1/3 bias is optimal for LCD displays with four common terminals (1/4 duty). Waveform is shown
in Figure 23-6. SEG0 - COM0 is the voltage across a segment that is on and SEG0 - COM1 is
the voltage across a segment that is off.
V
LCD
GND
V
LCD
1
/
2
V
LCD
GND
V
LCD
1
/
2
V
LCD
GND
-1
/
2
V
LCD
-V
LCD
SEG0
COM0
SEG0 - COM0
Frame Frame
V
LCD
GND
V
LCD
1
/
2
V
LCD
GND
V
LCD
1
/
2
V
LCD
GND
-1
/
2
V
LCD
-V
LCD
SEG0
COM1
SEG0 - COM1
Frame Frame
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
-
1
/
3
V
LCD
-
2
/
3
V
LCD
-V
LCD
SEG0
COM0
SEG0 - COM0
Frame Frame
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
-
1
/
3
V
LCD
-
2
/
3
V
LCD
-V
LCD
SEG0
COM1
SEG0 - COM1
Frame Frame
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Figure 23-6. Driving a LCD with Four Common Terminals
23.2.5 Low Power Waveform
To reduce toggle activity and hence power consumption a low power waveform can be selected
by writing LCDAB to one. Low power waveform requires two subsequent frames with the same
display data to obtain zero DC voltage. Consequently data latching and Interrupt Flag is only set
every second frame. Default and low power waveform is shown in Figure 23-7 for 1/3 duty and
1/3 bias. For other selections of duty and bias, the effect is similar.
Figure 23-7. Default and Low Power Waveform
23.2.6 Operation in Sleep Mode
When synchronous LCD clock is selected (LCDCS = 0) the LCD display will operate in Idle
mode and Power-save mode with any clock source.
An asynchronous clock from TOSC1 can be selected as LCD clock by writing the LCDCS bit to
one when Calibrated Internal RC Oscillator is selected as system clock source. The LCD will
then operate in Idle mode, ADC Noise Reduction mode and Power-save mode.
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
-
1
/
3
V
LCD
-
2
/
3
V
LCD
-V
LCD
SEG0
COM0
SEG0 - COM0
Frame Frame
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
-
1
/
3
V
LCD
-
2
/
3
V
LCD
-V
LCD
SEG0
COM1
SEG0 - COM1
Frame Frame
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
-
1
/
3
V
LCD
-
2
/
3
V
LCD
-V
LCD
SEG0
COM0
SEG0 - COM0
Frame Frame
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
V
LCD
2
/
3
V
LCD
1
/
3
V
LCD
GND
-
1
/
3
V
LCD
-
2
/
3
V
LCD
-V
LCD
SEG0
COM0
SEG0 - COM0
Frame Frame
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When EXCLK in ASSR Register is written to one, and asynchronous clock is selected, the exter-
nal clock input buffer is enabled and an external clock can be input on Timer Oscillator 1
(TOSC1) pin instead of a 32kHz crystal. See “Asynchronous Operation of Timer/Counter2” on
page 151 for further details.
Before entering Power-down mode, Standby mode or ADC Noise Reduction mode with synchro-
nous LCD clock selected, the user have to disable the LCD. Refer to “Disabling the LCD” on
page 237.
23.2.7 Display Blanking
When LCDBL is written to one, the LCD is blanked after completing the current frame. All seg-
ments and common pins are connected to GND, discharging the LCD. Display memory is
preserved. Display blanking should be used before disabling the LCD to avoid DC voltage
across segments, and a slowly fading image.
23.2.8 Port Mask
For LCD with less than 25/40 segment terminals, it is possible to mask some of the unused pins
and use them as ordinary port pins instead. Refer to Table 23-3 for details. Unused common
pins are automatically configured as port pins.
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23.3 LCD Usage
The following section describes how to use the LCD.
23.3.1 LCD Initialization
Prior to enabling the LCD some initialization must be preformed. The initialization pro-
cess normally consists of setting the frame rate, duty, bias and port mask. LCD contrast
is set initially, but can also be adjusted during operation.
Consider the following LCD as an example:
Figure 23-8.
Display: TN Positive, Reflective
Number of common terminals: 3
Number of segment terminals: 21
Bias system: 1/3 Bias
Drive system: 1/3 Duty
Operating voltage: 3.0 ± 0.3 V
1b
1c
2a
2b
2c2e
2f
2d
2g
COM3
COM0 COM1 COM2
SEG0
SEG1
SEG2
1b,1c
2c
2f
2a
2d
2g
2b
2e
..
COM2
SEG0
SEG1
SEG2
ATmega329
COM1
COM0
Connection table
LCD
51 50 49
48
47
46
45
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Note: 1. See “About Code Examples” on page 9.
Before a re-initialization is done, the LCD controller/driver should be disabled
Assembly Code Example(1)
LCD_Init:
; Use 32 kHz crystal oscillator
; 1/3 Bias and 1/3 duty, SEG21:SEG24 is used as port pins
ldi r16, (1<<LCDCS) | (1<<LCDMUX1)| (1<<LCDPM2)
sts LCDCRB, r16
; Using 16 as prescaler selection and 7 as LCD Clock Divide
; gives a frame rate of 49 Hz
ldi r16, (1<<LCDCD2) | (1<<LCDCD1)
sts LCDFRR, r16
; Set segment drive time to 125 µs and output voltage to 3.3 V
ldi r16, (1<<LCDDC1) | (1<<LCDCC3) | (1<<LCDCC2) | (1<<LCDCC1)
sts LCDCCR, r16
; Enable LCD, default waveform and no interrupt enabled
ldi r16, (1<<LCDEN)
sts LCDCRA, r16
ret
C Code Example(1)
Void LCD_Init(void);
{
/* Use 32 kHz crystal oscillator */
/* 1/3 Bias and 1/3 duty, SEG21:SEG24 is used as port pins */
LCDCRB = (1<<LCDCS) | (1<<LCDMUX1)| (1<<LCDPM2);
/* Using 16 as prescaler selection and 7 as LCD Clock Divide */
/* gives a frame rate of 49 Hz */
LCDFRR = (1<<LCDCD2) | (1<<LCDCD1);
/* Set segment drive time to 125 µs and output voltage to 3.3 V*/
LCDCCR = (1<<LCDDC1) | (1<<LCDCC3) | (1<<LCDCC2) | (1<<LCDCC1);
/* Enable LCD, default waveform and no interrupt enabled */
LCDCRA = (1<<LCDEN);
}
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23.3.2 Updating the LCD
Display memory (LCDDR0, LCDDR1, ..), LCD Blanking (LCDBL), Low power waveform
(LCDAB) and contrast control (LCDCCR) are latched prior to every new frame. There
are no restrictions on writing these LCD Register locations, but an LCD data update may
be split between two frames if data are latched while an update is in progress. To avoid
this, an interrupt routine can be used to update Display memory, LCD Blanking, Low
power waveform, and contrast control, just after data are latched.
In the example below we assume SEG10 and COM1 and SEG4 in COM0 are the only
segments changed from frame to frame. Data are stored in r20 and r21 for simplicity
Note: 1. See “About Code Examples” on page 9.
23.3.3 Disabling the LCD
In some application it may be necessary to disable the LCD. This is the case if the MCU
enters Power-down mode where no clock source is present.
The LCD should be completely discharged before being disabled. No DC voltage should
be left across any segment. The best way to achieve this is to use the LCD Blanking fea-
ture that drives all segment pins and common pins to GND.
When the LCD is disabled, port function is activated again. Therefore, the user must
check that port pins connected to a LCD terminal are either tri-state or output low (sink).
Assembly Code Example(1)
LCD_update:
; LCD Blanking and Low power waveform are unchanged.
; Update Display memory.
sts LCDDR0, r20
sts LCDDR6, r21
ret
C Code Example(1)
Void LCD_update(unsigned char data1, data2);
{
/* LCD Blanking and Low power waveform are unchanged. */
/* Update Display memory. */
LCDDR0 = data1;
LCDDR6 = data2;
}
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Note: 1. See “About Code Examples” on page 9.
Assembly Code Example(1)
LCD_disable:
; Wait until a new frame is started.
Wait_1:
lds r16, LCDCRA
sbrs r16, LCDIF
rjmp Wait_1
; Set LCD Blanking and clear interrupt flag
; by writing a logical one to the flag.
ldi r16, (1<<LCDEN)|(1<<LCDIF)|(1<<LCDBL)
sts LCDCRA, r16
; Wait until LCD Blanking is effective.
Wait_2:
lds r16, LCDCRA
sbrs r16, LCDIF
rjmp Wait_2
; Disable LCD.
ldi r16, (0<<LCDEN)
sts LCDCRA, r16
ret
C Code Example(1)
Void LCD_disable(void);
{
/* Wait until a new frame is started. */
while ( !(LCDCRA & (1<<LCDIF)) )
;
/* Set LCD Blanking and clear interrupt flag */
/* by writing a logical one to the flag. */
LCDCRA = (1<<LCDEN)|(1<<LCDIF)|(1<<LCDBL);
/* Wait until LCD Blanking is effective. */
while ( !(LCDCRA & (1<<LCDIF)) )
;
/* Disable LCD */
LCDCRA = (0<<LCDEN);
}
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23.4 Register Description
23.4.1 LCDCRA – LCD Control and Status Register A
• Bit 7 – LCDEN: LCD Enable
Writing this bit to one enables the LCD Controller/Driver. By writing it to zero, the LCD is turned
off immediately. Turning the LCD Controller/Driver off while driving a display, enables ordinary
port function, and DC voltage can be applied to the display if ports are configured as output. It is
recommended to drive output to ground if the LCD Controller/Driver is disabled to discharge the
display.
• Bit 6 – LCDAB: LCD Low Power Waveform
When LCDAB is written logic zero, the default waveform is output on the LCD pins. When
LCDAB is written logic one, the Low Power Waveform is output on the LCD pins. If this bit is
modified during display operation the change takes place at the beginning of a new frame.
• Bit 5 – Reserved Bit
This bit is reserved bit in the ATmega329/3290/649/6490 and will always read as zero.
• Bit 4 – LCDIF: LCD Interrupt Flag
This bit is set by hardware at the beginning of a new frame, at the same time as the display data
is updated. The LCD Start of Frame Interrupt is executed if the LCDIE bit and the I-bit in SREG
are set. LCDIF is cleared by hardware when executing the corresponding Interrupt Handling
Vector. Alternatively, writing a logical one to the flag clears LCDIF. Beware that if doing a Read-
Modify-Write on LCDCRA, a pending interrupt can be disabled. If Low Power Waveform is
selected the Interrupt Flag is set every second frame.
• Bit 3 – LCDIE: LCD Interrupt Enable
When this bit is written to one and the I-bit in SREG is set, the LCD Start of Frame Interrupt is
enabled.
• Bits 2:1 – Reserved Bits
These bits are reserved bits in the ATmega329/3290/649/6490 and will always read as zero.
• Bit 0 – LCDBL: LCD Blanking
When this bit is written to one, the display will be blanked after completion of a frame. All seg-
ment and common pins will be driven to ground.
23.4.2 LCDCRB – LCD Control and Status Register B
Note: Bit 3, LCDPM3 is only available in ATmega3290/6490.
Bit 76543210
(0xE4) LCDEN LCDAB – LCDIF LCDIE – – LCDBL LCDCRA
Read/Write R/W R/W R R/W R/W R R R/W
Initial Value00000000
Bit 7 6 5 4 3 2 1 0
(0xE5) LCDCS LCD2B LCDMUX1 LCDMUX0 LCDPM3 LCDPM2 LCDPM1 LCDPM0 LCDCRB
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Val-
ue
000 0 0000
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• Bit 7 – LCDCS: LCD Clock Select
When this bit is written to zero, the system clock is used. When this bit is written to one, the
external asynchronous clock source is used. The asynchronous clock source is either
Timer/Counter Oscillator or external clock, depending on EXCLK in ASSR. See “Asynchronous
Operation of Timer/Counter2” on page 151 for further details.
• Bit 6 – LCD2B: LCD 1/2 Bias Select
When this bit is written to zero, 1/3 bias is used. When this bit is written to one, ½ bias is used.
Refer to the LCD Manufacture for recommended bias selection.
• Bit 5:4 – LCDMUX1:0: LCD Mux Select
The LCDMUX1:0 bits determine the duty cycle. Common pins that are not used are ordinary port
pins. The different duty selections are shown in Table 23-2.
Note: 1. 1/2 bias when LCD2B is written to one and 1/3 otherwise.
• Bits 3:0 – LCDPM3:0: LCD Port Mask
The LCDPM3:0 bits determine the number of port pins to be used as segment drivers. The dif-
ferent selections are shown in Table 23-3. Unused pins can be used as ordinary port pins.
Table 23-2. LCD Duty Select
LCDMUX1 LCDMUX0 Duty Bias COM Pin I/O Port Pin
0 0 Static Static COM0 COM1:3
0 1 1/2 1/2 or 1/3(1) COM0:1 COM2:3
101/31/2
or 1/3(1) COM0:2 COM3
111/41/2
or 1/3(1) COM0:3 None
Table 23-3. LCD Port Mask (Values in bold are only available in ATmega3290/6490)
LCDPM3 LCDPM2 LCDPM1 LCDPM0
I/O Port in Use as
Segment Driver
Maximum Number
of Segments
00 0 0 SEG0:12 13
00 0 1 SEG0:14 15
00 1 0 SEG0:16 17
0011 SEG0:1819
01 0 0 SEG0:20 21
01 0 1 SEG0:22 23
01 1 0 SEG0:23 24
01 1 1 SEG0:24 25
1 0 0 0 SEG0:26 27
1 0 0 1 SEG0:28 29
1 0 1 0 SEG0:30 31
1 0 1 1 SEG0:32 33
1 1 0 0 SEG0:34 35
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Note: 1. LCDPM3 is reserved and will always read as zero in ATmega329/649.
23.4.3 LCDFRR – LCD Frame Rate Register
• Bit 7 – Reserved Bit
This bit is reserved bit in the ATmega329/3290/649/6490 and will always read as zero.
• Bits 6:4 – LCDPS2:0: LCD Prescaler Select
The LCDPS2:0 bits selects tap point from a prescaler. The prescaled output can be further
divided by setting the clock divide bits (LCDCD2:0). The different selections are shown in Table
23-4. Together they determine the prescaled LCD clock (clkLCD_PS), which is clocking the LCD
module.
• Bit 3 – Reserved Bit
This bit is reserved bit in the ATmega329/3290/649/6490 and will always read as zero.
• Bits 2:0 – LCDCD2:0: LCD Clock Divide 2, 1, and 0
The LCDCD2:0 bits determine division ratio in the clock divider. The various selections are
shown in Table 23-5. This Clock Divider gives extra flexibility in frame rate selection.
1 1 0 1 SEG0:36 37
1 1 1 0 SEG0:38 39
1 1 1 1 SEG0:39 40
Table 23-3. LCD Port Mask (Values in bold are only available in ATmega3290/6490)
LCDPM3 LCDPM2 LCDPM1 LCDPM0
I/O Port in Use as
Segment Driver
Maximum Number
of Segments
Bit 76543210
(0xE6) – LCDPS2 LCDPS1 LCDPS0 – LCDCD2 LCDCD1 LCDCD0 LCDFRR
Read/Write R R/W R/W R/W R R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 23-4. LCD Prescaler Select
LCDPS2 LCDPS1 LCDPS0
Output from
Prescaler
clkLCD/N
Applied Prescaled LCD Clock
Frequency when LCDCD2:0 = 0,
Duty = 1/4, and Frame Rate = 64 Hz
000clk
LCD/16 8.1kHz
001clk
LCD/64 33kHz
010clk
LCD/12866kHz
011clk
LCD/256 130kHz
100clk
LCD/512 260kHz
101clk
LCD/1024 520kHz
110clk
LCD/20481MHz
111clk
LCD/4096 2MHz
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The frame frequency can be calculated by the following equation:
Where:
N = prescaler divider (16, 64, 128, 256, 512, 1024, 2048, or 4096).
K = 8 for duty = 1/4, 1/2, and static.
K = 6 for duty = 1/3.
D = Division factor (see Table 23-5)
This is a very flexible scheme, and users are encouraged to calculate their own table to investi-
gate the possible frame rates from the formula above. Note when using 1/3 duty the frame rate
is increased with 33% when Frame Rate Register is constant. Example of frame rate calculation
is shown in Table 23-6.
Table 23-5. LCD Clock Divide
LCDCD2 LCDCD1 LCDCD0
Output from
Prescaler
divided by (D) :
clkLCD = 32.768kHz, N = 16, and
Duty = 1/4, gives a frame rate of:
0 0 0 1 256Hz
001 2 128Hz
010 3 85.3Hz
011 4 64Hz
1 0 0 5 51.2Hz
1 0 1 6 42.7Hz
1 1 0 7 36.6Hz
111 832Hz
Table 23-6. Example of frame rate calculation
clkLCD duty K N LCDCD2:0 D Frame Rate
4MHz 1/4 82048011 4 4000000/(8*2048*4) = 61 Hz
4MHz 1/3 6 2048011 4 4000000/(6*2048*4) = 81 Hz
32.768kHz Static 816 000 1 32768/(8*16*1) = 256 Hz
32.768kHz 1/2 816 100 5 32768/(8*16*5) = 51 Hz
fframe
fclkLCD
KND⋅⋅()
--------------------------=
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23.4.4 LCDCCR – LCD Contrast Control Register
• Bits 7:5 – LCDDC2:0: LDC Display Configuration
The LCDDC2:0 bits determine the amount of time the LCD drivers are turned on for each volt-
age transition on segment and common pins. A short drive time will lead to lower power
consumption, but displays with high internal resistance may need longer drive time to achieve
satisfactory contrast. Note that the drive time will never be longer than one half prescaled LCD
clock period, even if the selected drive time is longer. When using static duty or blanking, drive
time will always be one half prescaled LCD clock period.
New values take effect immediately, and can cause small glitches in the display output. This can
be avoided by setting the LCDBL in LCDCRA, and wait to the next start of frame before chang-
ing LCDDC2:0.
Note: The drive time will be longer dependent on oscillator startup time.
• Bit 4 – Reserved Bit
This bit is reserved in the ATmega329/3290/649/6490 and will always read as zero.
• Bits 3:0 – LCDCC3:0: LCD Contrast Control
The LCDCC3:0 bits determine the maximum voltage VLCD on segment and common pins. The
different selections are shown in Table 23-8. New values take effect every beginning of a new
frame.
Bit 76543210
(0xE7) LCDDC2 LCDDC1 LCDDC0 – LCDCC3 LCDCC2 LCDCC1 LCDCC0 LCDCCR
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
Table 23-7. LCD Display Configuration
LCDDC2 LCDDC1 LCDDC0 Nominal drive time
0 0 0 300µs
0 0 1 70µs
0 1 0 150µs
0 1 1 450µs
1 0 0 575µs
101850µs
1 1 0 1150µs
11150% of clk
LCD_PS
Table 23-8. LCD Contrast Control
LCDCC3 LCDCC2 LCDCC1 LCDCC0 Maximum Voltage VLCD
0 0 0 0 2.60
0 0 0 1 2.65
0 0 1 0 2.70
0 0 1 1 2.75
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23.4.5 LCD Memory Mapping
Write a LCD memory bit to one and the corresponding segment will be energized (visible).
Unused LCD Memory bits for the actual display can be used freely as storage.
0100 2.80
0101 2.85
0 1 1 0 2.90
0 1 1 1 2.95
1 0 0 0 3.00
1 0 0 1 3.05
1 0 1 0 3.10
1 0 1 1 3.15
1 1 0 0 3.20
1 1 0 1 3.25
1 1 1 0 3.30
1 1 1 1 3.35
Table 23-8. LCD Contrast Control (Continued)
LCDCC3 LCDCC2 LCDCC1 LCDCC0 Maximum Voltage VLCD
Bit 76543210
COM3SEG339 SEG338 SEG337 SEG336 SEG335 SEG334 SEG333 SEG332 LCDDR19
COM3SEG331 SEG330 SEG329 SEG328 SEG327 SEG326 SEG325 SEG324 LCDDR18
COM3SEG323 SEG322 SEG321 SEG320 SEG319 SEG318 SEG317 SEG316 LCDDR17
COM3SEG315 SEG314 SEG313 SEG312 SEG311 SEG310 SEG309 SEG308 LCDDR16
COM3SEG307 SEG306 SEG305 SEG304 SEG303 SEG302 SEG301 SEG300 LCDDR15
COM2SEG239 SEG238 SEG237 SEG236 SEG235 SEG234 SEG233 SEG232 LCDDR14
COM2SEG231 SEG230 SEG229 SEG228 SEG227 SEG226 SEG225 SEG224 LCDDR13
COM2SEG223 SEG222 SEG221 SEG220 SEG219 SEG218 SEG217 SEG216 LCDDR12
COM2SEG215 SEG214 SEG213 SEG212 SEG211 SEG210 SEG209 SEG208 LCDDR11
COM2SEG207 SEG206 SEG205 SEG204 SEG203 SEG202 SEG201 SEG200 LCDDR10
COM1SEG139 SEG138 SEG137 SEG136 SEG135 SEG134 SEG133 SEG132 LCDDR9
COM1SEG131 SEG130 SEG129 SEG128 SEG127 SEG126 SEG125 SEG124 LCDDR8
COM1SEG123 SEG122 SEG121 SEG120 SEG119 SEG118 SEG117 SEG116 LCDDR7
COM1SEG115 SEG114 SEG113 SEG112 SEG111 SEG110 SEG109 SEG108 LCDDR6
COM1SEG107 SEG106 SEG105 SEG104 SEG103 SEG102 SEG101 SEG100 LCDDR5
COM0SEG039 SEG038 SEG037 SEG036 SEG035 SEG034 SEG033 SEG032 LCDDR4
COM0SEG031 SEG030 SEG029 SEG028 SEG027 SEG026 SEG025 SEG024 LCDDR3
COM0SEG023 SEG022 SEG021 SEG020 SEG019 SEG018 SEG017 SEG016 LCDDR2
COM0SEG015 SEG014 SEG013 SEG012 SEG011 SEG010 SEG009 SEG008 LCDDR1
COM0SEG007 SEG006 SEG005 SEG004 SEG003 SEG002 SEG001 SEG000 LCDDR0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 00000000
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24. JTAG Interface and On-chip Debug System
24.1 Features
•JTAG (IEEE std. 1149.1 Compliant) Interface
•Boundary-scan Capabilities According to the IEEE std. 1149.1 (JTAG) Standard
•Debugger Access to:
•All Internal Peripheral Units
•Internal and External RAM
•The Internal Register File
•Program Counter
•EEPROM and Flash Memories
•Extensive On-chip Debug Support for Break Conditions, Including
•AVR Break Instruction
•Break on Change of Program Memory Flow
•Single Step Break
•Program Memory Break Points on Single Address or Address Range
•Data Memory Break Points on Single Address or Address Range
•Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG Interface
•On-chip Debugging Supported by AVR Studio®
24.2 Overview
The AVR IEEE std. 1149.1 compliant JTAG interface can be used for
• Testing PCBs by using the JTAG Boundary-scan capability
• Programming the non-volatile memories, Fuses and Lock bits
• On-chip debugging
A brief description is given in the following sections. Detailed descriptions for Programming via
the JTAG interface, and using the Boundary-scan Chain can be found in the sections “Program-
ming via the JTAG Interface” on page 313 and “IEEE 1149.1 (JTAG) Boundary-scan” on page
251, respectively. The On-chip Debug support is considered being private JTAG instructions,
and distributed within ATMEL and to selected third party vendors only.
Figure 24-1 shows a block diagram of the JTAG interface and the On-chip Debug system. The
TAP Controller is a state machine controlled by the TCK and TMS signals. The TAP Controller
selects either the JTAG Instruction Register or one of several Data Registers as the scan chain
(Shift Register) between the TDI – input and TDO – output. The Instruction Register holds JTAG
instructions controlling the behavior of a Data Register.
The ID-Register, Bypass Register, and the Boundary-scan Chain are the Data Registers used
for board-level testing. The JTAG Programming Interface (actually consisting of several physical
and virtual Data Registers) is used for serial programming via the JTAG interface. The Internal
Scan Chain and Break Point Scan Chain are used for On-chip debugging only.
24.3 Test Access Port – TAP
The JTAG interface is accessed through four of the AVR’s pins. In JTAG terminology, these pins
constitute the Test Access Port – TAP. These pins are:
• TMS: Test mode select. This pin is used for navigating through the TAP-controller state
machine.
• TCK: Test Clock. JTAG operation is synchronous to TCK.
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• TDI: Test Data In. Serial input data to be shifted in to the Instruction Register or Data
Register (Scan Chains).
• TDO: Test Data Out. Serial output data from Instruction Register or Data Register.
The IEEE std. 1149.1 also specifies an optional TAP signal; TRST – Test ReSeT – which is not
provided.
When the JTAGEN fuse is unprogrammed, these four TAP pins are normal port pins and the
TAP controller is in reset. When programmed and the JTD bit in MCUCSR is cleared, the TAP
pins are internally pulled high and the JTAG is enabled for Boundary-scan and programming.
The device is shipped with this fuse programmed.
For the On-chip Debug system, in addition to the JTAG interface pins, the RESET pin is moni-
tored by the debugger to be able to detect external reset sources. The debugger can also pull
the RESET pin low to reset the whole system, assuming only open collectors on the reset line
are used in the application.
Figure 24-1. Block Diagram
TAP
CONTROLLER
TDI
TDO
TCK
TMS
FLASH
MEMORY
AVR CPU
DIGITAL
PERIPHERAL
UNITS
JTAG / AVR CORE
COMMUNICATION
INTERFACE
BREAKPOINT
UNIT FLOW CONTROL
UNIT
OCD STATUS
AND CONTROL
INTERNAL
SCAN
CHAIN
M
U
X
INSTRUCTION
REGISTER
ID
REGISTER
BYPASS
REGISTER
JTAG PROGRAMMING
INTERFACE
PC
Instruction
Address
Data
BREAKPOINT
SCAN CHAIN
ADDRESS
DECODER
ANALOG
PERIPHERIAL
UNITS
I/O PORT 0
I/O PORT n
BOUNDARY SCAN CHAIN
Analog inputs
Control & Clock lines
DEVICE BOUNDARY
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Figure 24-2. TAP Controller State Diagram
24.4 TAP Controller
The TAP controller is a 16-state finite state machine that controls the operation of the Boundary-
scan circuitry, JTAG programming circuitry, or On-chip Debug system. The state transitions
depicted in Figure 24-2 depend on the signal present on TMS (shown adjacent to each state
transition) at the time of the rising edge at TCK. The initial state after a Power-on Reset is Test-
Logic-Reset.
As a definition in this document, the LSB is shifted in and out first for all Shift Registers.
Assuming Run-Test/Idle is the present state, a typical scenario for using the JTAG interface is:
• At the TMS input, apply the sequence 1, 1, 0, 0 at the rising edges of TCK to enter the Shift
Instruction Register – Shift-IR state. While in this state, shift the four bits of the JTAG
instructions into the JTAG Instruction Register from the TDI input at the rising edge of TCK.
The TMS input must be held low during input of the 3 LSBs in order to remain in the Shift-IR
state. The MSB of the instruction is shifted in when this state is left by setting TMS high.
While the instruction is shifted in from the TDI pin, the captured IR-state 0x01 is shifted out
on the TDO pin. The JTAG Instruction selects a particular Data Register as path between
TDI and TDO and controls the circuitry surrounding the selected Data Register.
Test-Logic-Reset
Run-Test/Idle
Shift-DR
Exit1-DR
Pause-DR
Exit2-DR
Update-DR
Select-IR Scan
Capture-IR
Shift-IR
Exit1-IR
Pause-IR
Exit2-IR
Update-IR
Select-DR Scan
Capture-DR
0
1
011 1
00
00
11
10
1
1
0
1
0
0
10
1
1
0
1
0
0
00
11
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• Apply the TMS sequence 1, 1, 0 to re-enter the Run-Test/Idle state. The instruction is
latched onto the parallel output from the Shift Register path in the Update-IR state. The Exit-
IR, Pause-IR, and Exit2-IR states are only used for navigating the state machine.
• At the TMS input, apply the sequence 1, 0, 0 at the rising edges of TCK to enter the Shift
Data Register – Shift-DR state. While in this state, upload the selected Data Register
(selected by the present JTAG instruction in the JTAG Instruction Register) from the TDI
input at the rising edge of TCK. In order to remain in the Shift-DR state, the TMS input must
be held low during input of all bits except the MSB. The MSB of the data is shifted in when
this state is left by setting TMS high. While the Data Register is shifted in from the TDI pin,
the parallel inputs to the Data Register captured in the Capture-DR state is shifted out on the
TDO pin.
• Apply the TMS sequence 1, 1, 0 to re-enter the Run-Test/Idle state. If the selected Data
Register has a latched parallel-output, the latching takes place in the Update-DR state. The
Exit-DR, Pause-DR, and Exit2-DR states are only used for navigating the state machine.
As shown in the state diagram, the Run-Test/Idle state need not be entered between selecting
JTAG instruction and using Data Registers, and some JTAG instructions may select certain
functions to be performed in the Run-Test/Idle, making it unsuitable as an Idle state.
Note: Independent of the initial state of the TAP Controller, the Test-Logic-Reset state can always be
entered by holding TMS high for five TCK clock periods.
For detailed information on the JTAG specification, refer to the literature listed in “Bibliography”
on page 250.
24.5 Using the Boundary-scan Chain
A complete description of the Boundary-scan capabilities are given in the section “IEEE 1149.1
(JTAG) Boundary-scan” on page 251.
24.6 Using the On-chip Debug System
As shown in Figure 24-1, the hardware support for On-chip Debugging consists mainly of
• A scan chain on the interface between the internal AVR CPU and the internal peripheral
units.
• Break Point unit.
• Communication interface between the CPU and JTAG system.
All read or modify/write operations needed for implementing the Debugger are done by applying
AVR instructions via the internal AVR CPU Scan Chain. The CPU sends the result to an I/O
memory mapped location which is part of the communication interface between the CPU and the
JTAG system.
The Break Point Unit implements Break on Change of Program Flow, Single Step Break, two
Program Memory Break Points, and two combined Break Points. Together, the four Break
Points can be configured as either:
• 4 single Program Memory Break Points.
• 3 Single Program Memory Break Point + 1 single Data Memory Break Point.
• 2 single Program Memory Break Points + 2 single Data Memory Break Points.
• 2 single Program Memory Break Points + 1 Program Memory Break Point with mask (“range
Break Point”).
• 2 single Program Memory Break Points + 1 Data Memory Break Point with mask (“range
Break Point”).
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A debugger, like the AVR Studio, may however use one or more of these resources for its inter-
nal purpose, leaving less flexibility to the end-user.
A list of the On-chip Debug specific JTAG instructions is given in “On-chip Debug Specific JTAG
Instructions” on page 249.
The JTAGEN Fuse must be programmed to enable the JTAG Test Access Port. In addition, the
OCDEN Fuse must be programmed and no Lock bits must be set for the On-chip debug system
to work. As a security feature, the On-chip debug system is disabled when either of the LB1 or
LB2 Lock bits are set. Otherwise, the On-chip debug system would have provided a back-door
into a secured device.
The AVR Studio enables the user to fully control execution of programs on an AVR device with
On-chip Debug capability, AVR In-Circuit Emulator, or the built-in AVR Instruction Set Simulator.
AVR Studio® supports source level execution of Assembly programs assembled with Atmel Cor-
poration’s AVR Assembler and C programs compiled with third party vendors’ compilers.
AVR Studio runs under Microsoft® Windows® 95/98/2000, Windows NT® and Windows XP®.
For a full description of the AVR Studio, please refer to the AVR Studio User Guide. Only high-
lights are presented in this document.
All necessary execution commands are available in AVR Studio, both on source level and on
disassembly level. The user can execute the program, single step through the code either by
tracing into or stepping over functions, step out of functions, place the cursor on a statement and
execute until the statement is reached, stop the execution, and reset the execution target. In
addition, the user can have an unlimited number of code Break Points (using the BREAK
instruction) and up to two data memory Break Points, alternatively combined as a mask (range)
Break Point.
24.7 On-chip Debug Specific JTAG Instructions
The On-chip debug support is considered being private JTAG instructions, and distributed within
ATMEL and to selected third party vendors only. Instruction opcodes are listed for reference.
24.7.1 PRIVATE0; 0x8
Private JTAG instruction for accessing On-chip debug system.
24.7.2 PRIVATE1; 0x9
Private JTAG instruction for accessing On-chip debug system.
24.7.3 PRIVATE2; 0xA
Private JTAG instruction for accessing On-chip debug system.
24.7.4 PRIVATE3; 0xB
Private JTAG instruction for accessing On-chip debug system.
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24.8 Using the JTAG Programming Capabilities
Programming of AVR parts via JTAG is performed via the 4-pin JTAG port, TCK, TMS, TDI, and
TDO. These are the only pins that need to be controlled/observed to perform JTAG program-
ming (in addition to power pins). It is not required to apply 12V externally. The JTAGEN Fuse
must be programmed and the JTD bit in the MCUCR Register must be cleared to enable the
JTAG Test Access Port.
The JTAG programming capability supports:
• Flash programming and verifying.
• EEPROM programming and verifying.
• Fuse programming and verifying.
• Lock bit programming and verifying.
The Lock bit security is exactly as in parallel programming mode. If the Lock bits LB1 or LB2 are
programmed, the OCDEN Fuse cannot be programmed unless first doing a chip erase. This is a
security feature that ensures no back-door exists for reading out the content of a secured
device.
The details on programming through the JTAG interface and programming specific JTAG
instructions are given in the section “Programming via the JTAG Interface” on page 313.
24.9 Bibliography
For more information about general Boundary-scan, the following literature can be consulted:
• IEEE: IEEE Std. 1149.1-1990. IEEE Standard Test Access Port and Boundary-scan
Architecture, IEEE, 1993.
Colin Maunder: The Board Designers Guide to Testable Logic Circuits, Addison-Wesley, 1992.
24.10 Register Description
24.10.1 OCDR – On-chip Debug Register
The OCDR Register provides a communication channel from the running program in the micro-
controller to the debugger. The CPU can transfer a byte to the debugger by writing to this
location. At the same time, an internal flag; I/O Debug Register Dirty – IDRD – is set to indicate
to the debugger that the register has been written. When the CPU reads the OCDR Register the
7 LSB will be from the OCDR Register, while the MSB is the IDRD bit. The debugger clears the
IDRD bit when it has read the information.
In some AVR devices, this register is shared with a standard I/O location. In this case, the OCDR
Register can only be accessed if the OCDEN Fuse is programmed, and the debugger enables
access to the OCDR Register. In all other cases, the standard I/O location is accessed.
Refer to the debugger documentation for further information on how to use this register.
Bit 7 6543210
0x31 (0x51) MSB/IDRD LSB OCDR
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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25. IEEE 1149.1 (JTAG) Boundary-scan
25.1 Features
•JTAG (IEEE std. 1149.1 compliant) Interface
•Boundary-scan Capabilities According to the JTAG Standard
•Full Scan of all Port Functions as well as Analog Circuitry having Off-chip Connections
•Supports the Optional IDCODE Instruction
•Additional Public AVR_RESET Instruction to Reset the AVR
25.2 System Overview
The Boundary-scan chain has the capability of driving and observing the logic levels on the digi-
tal I/O pins, as well as the boundary between digital and analog logic for analog circuitry having
off-chip connections. At system level, all ICs having JTAG capabilities are connected serially by
the TDI/TDO signals to form a long Shift Register. An external controller sets up the devices to
drive values at their output pins, and observe the input values received from other devices. The
controller compares the received data with the expected result. In this way, Boundary-scan pro-
vides a mechanism for testing interconnections and integrity of components on Printed Circuits
Boards by using the four TAP signals only.
The four IEEE 1149.1 defined mandatory JTAG instructions IDCODE, BYPASS, SAMPLE/PRE-
LOAD, and EXTEST, as well as the AVR specific public JTAG instruction AVR_RESET can be
used for testing the Printed Circuit Board. Initial scanning of the Data Register path will show the
ID-Code of the device, since IDCODE is the default JTAG instruction. It may be desirable to
have the AVR device in reset during test mode. If not reset, inputs to the device may be deter-
mined by the scan operations, and the internal software may be in an undetermined state when
exiting the test mode. Entering reset, the outputs of any port pin will instantly enter the high
impedance state, making the HIGHZ instruction redundant. If needed, the BYPASS instruction
can be issued to make the shortest possible scan chain through the device. The device can be
set in the reset state either by pulling the external RESET pin low, or issuing the AVR_RESET
instruction with appropriate setting of the Reset Data Register.
The EXTEST instruction is used for sampling external pins and loading output pins with data.
The data from the output latch will be driven out on the pins as soon as the EXTEST instruction
is loaded into the JTAG IR-Register. Therefore, the SAMPLE/PRELOAD should also be used for
setting initial values to the scan ring, to avoid damaging the board when issuing the EXTEST
instruction for the first time. SAMPLE/PRELOAD can also be used for taking a snapshot of the
external pins during normal operation of the part.
The JTAGEN Fuse must be programmed and the JTD bit in the I/O Register MCUCR must be
cleared to enable the JTAG Test Access Port.
When using the JTAG interface for Boundary-scan, using a JTAG TCK clock frequency higher
than the internal chip frequency is possible. The chip clock is not required to run.
25.3 Data Registers
The Data Registers relevant for Boundary-scan operations are:
• Bypass Register
• Device Identification Register
• Reset Register
• Boundary-scan Chain
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25.3.1 Bypass Register
The Bypass Register consists of a single Shift Register stage. When the Bypass Register is
selected as path between TDI and TDO, the register is reset to 0 when leaving the Capture-DR
controller state. The Bypass Register can be used to shorten the scan chain on a system when
the other devices are to be tested.
25.3.2 Device Identification Register
Figure 25-1 shows the structure of the Device Identification Register.
Figure 25-1. The Format of the Device Identification Register
25.3.2.1 Version
Version is a 4-bit number identifying the revision of the component. The JTAG version number
follows the revision of the device. Revision A is 0x0, revision B is 0x1 and so on.
25.3.2.2 Part Number
The part number is a 16-bit code identifying the component. The JTAG Part Number for
ATmega329/3290/649/6490 is listed in Table 25-1.
25.3.2.3 Manufacturer ID
The Manufacturer ID is a 11-bit code identifying the manufacturer. The JTAG manufacturer ID
for ATMEL is listed in Table 25-2.
25.3.3 Reset Register
The Reset Register is a test Data Register used to reset the part. Since the AVR tri-states Port
Pins when reset, the Reset Register can also replace the function of the unimplemented optional
JTAG instruction HIGHZ.
A high value in the Reset Register corresponds to pulling the external Reset low. The part is
reset as long as there is a high value present in the Reset Register. Depending on the fuse set-
tings for the clock options, the part will remain reset for a reset time-out period (refer to “Clock
MSB LSB
Bit 31 28 27 12 11 1 0
Device ID Version Part Number Manufacturer ID 1
4 bits 16 bits 11 bits 1-bit
Table 25-1. AVR JTAG Part Number
Part Number JTAG Part Number (Hex)
ATmega329 0x9503
ATmega3290 0x9504
ATmega649 0x9603
ATmega6490 0x9604
Table 25-2. Manufacturer ID
Manufacturer JTAG Manufacturer ID (Hex)
ATME L 0 x 0 1 F
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Sources” on page 27) after releasing the Reset Register. The output from this Data Register is
not latched, so the reset will take place immediately, as shown in Figure 25-2.
Figure 25-2. Reset Register
25.3.4 Boundary-scan Chain
The Boundary-scan Chain has the capability of driving and observing the logic levels on the dig-
ital I/O pins, as well as the boundary between digital and analog logic for analog circuitry having
off-chip connections.
See “Boundary-scan Chain” on page 255 for a complete description.
25.4 Boundary-scan Specific JTAG Instructions
The Instruction Register is 4-bit wide, supporting up to 16 instructions. Listed below are the
JTAG instructions useful for Boundary-scan operation. Note that the optional HIGHZ instruction
is not implemented, but all outputs with tri-state capability can be set in high-impedant state by
using the AVR_RESET instruction, since the initial state for all port pins is tri-state.
As a definition in this data sheet, the LSB is shifted in and out first for all Shift Registers.
The OPCODE for each instruction is shown behind the instruction name in hex format. The text
describes which Data Register is selected as path between TDI and TDO for each instruction.
25.4.1 EXTEST; 0x0
Mandatory JTAG instruction for selecting the Boundary-scan Chain as Data Register for testing
circuitry external to the AVR package. For port-pins, Pull-up Disable, Output Control, Output
Data, and Input Data are all accessible in the scan chain. For Analog circuits having off-chip
connections, the interface between the analog and the digital logic is in the scan chain. The con-
tents of the latched outputs of the Boundary-scan chain is driven out as soon as the JTAG IR-
Register is loaded with the EXTEST instruction.
The active states are:
• Capture-DR: Data on the external pins are sampled into the Boundary-scan Chain.
• Shift-DR: The Internal Scan Chain is shifted by the TCK input.
• Update-DR: Data from the scan chain is applied to output pins.
DQ
From
TDI
ClockDR · AVR_RESET
To
TDO
From Other Internal and
External Reset Sources
Internal reset
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25.4.2 IDCODE; 0x1
Optional JTAG instruction selecting the 32 bit ID-Register as Data Register. The ID-Register
consists of a version number, a device number and the manufacturer code chosen by JEDEC.
This is the default instruction after power-up.
The active states are:
• Capture-DR: Data in the IDCODE Register is sampled into the Boundary-scan Chain.
• Shift-DR: The IDCODE scan chain is shifted by the TCK input.
25.4.3 SAMPLE_PRELOAD; 0x2
Mandatory JTAG instruction for pre-loading the output latches and taking a snap-shot of the
input/output pins without affecting the system operation. However, the output latches are not
connected to the pins. The Boundary-scan Chain is selected as Data Register.
The active states are:
• Capture-DR: Data on the external pins are sampled into the Boundary-scan Chain.
• Shift-DR: The Boundary-scan Chain is shifted by the TCK input.
• Update-DR: Data from the Boundary-scan chain is applied to the output latches. However,
the output latches are not connected to the pins.
25.4.4 AVR_RESET; 0xC
The AVR specific public JTAG instruction for forcing the AVR device into the Reset mode or
releasing the JTAG reset source. The TAP controller is not reset by this instruction. The one bit
Reset Register is selected as Data Register. Note that the reset will be active as long as there is
a logic “one” in the Reset Chain. The output from this chain is not latched.
The active states are:
• Shift-DR: The Reset Register is shifted by the TCK input.
25.4.5 BYPASS; 0xF
Mandatory JTAG instruction selecting the Bypass Register for Data Register.
The active states are:
• Capture-DR: Loads a logic “0” into the Bypass Register.
• Shift-DR: The Bypass Register cell between TDI and TDO is shifted.
25.5 Boundary-scan Related Register in I/O Memory
25.5.1 MCUCR – MCU Control Register
The MCU Control Register contains control bits for general MCU functions.
• Bit 7 – JTD: JTAG Interface Disable
When this bit is zero, the JTAG interface is enabled if the JTAGEN Fuse is programmed. If this
bit is one, the JTAG interface is disabled. In order to avoid unintentional disabling or enabling of
the JTAG interface, a timed sequence must be followed when changing this bit: The application
Bit 76543210
0x35 (0x55) JTD – – PUD – – IVSEL IVCE MCUCR
Read/Write R/W R R R/W R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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software must write this bit to the desired value twice within four cycles to change its value. Note
that this bit must not be altered when using the On-chip Debug system.
If the JTAG interface is left unconnected to other JTAG circuitry, the JTD bit should be set to
one. The reason for this is to avoid static current at the TDO pin in the JTAG interface.
25.5.2 MCUSR – MCU Status Register
The MCU Status Register provides information on which reset source caused an MCU reset.
• Bit 4 – JTRF: JTAG Reset Flag
This bit is set if a reset is being caused by a logic one in the JTAG Reset Register selected by
the JTAG instruction AVR_RESET. This bit is reset by a Power-on Reset, or by writing a logic
zero to the flag.
25.6 Boundary-scan Chain
The Boundary-scan chain has the capability of driving and observing the logic levels on the digi-
tal I/O pins, as well as the boundary between digital and analog logic for analog circuitry having
off-chip connection.
25.6.1 Scanning the Digital Port Pins
Figure 25-3 shows the Boundary-scan Cell for a bi-directional port pin with pull-up function. The
cell consists of a standard Boundary-scan cell for the Pull-up Enable – PUExn – function, and a
bi-directional pin cell that combines the three signals Output Control – OCxn, Output Data –
ODxn, and Input Data – IDxn, into only a two-stage Shift Register. The port and pin indexes are
not used in the following description
The Boundary-scan logic is not included in the figures in the Data Sheet. Figure 25-4 shows a
simple digital port pin as described in the section “I/O-Ports” on page 59. The Boundary-scan
details from Figure 25-3 replaces the dashed box in Figure 25-4.
When no alternate port function is present, the Input Data – ID – corresponds to the PINxn Reg-
ister value (but ID has no synchronizer), Output Data corresponds to the PORT Register, Output
Control corresponds to the Data Direction – DD Register, and the Pull-up Enable – PUExn – cor-
responds to logic expression PUD · DDxn · PORTxn.
Digital alternate port functions are connected outside the dotted box in Figure 25-4 to make the
scan chain read the actual pin value. For Analog function, there is a direct connection from the
external pin to the analog circuit, and a scan chain is inserted on the interface between the digi-
tal logic and the analog circuitry.
Bit 76543210
0x34 (0x54) –––JTRFWDRF BORF EXTRF PORF MCUSR
Read/Write R R R R/W R/W R/W R/W R/W
Initial Value 0 0 0 See Bit Description
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Figure 25-3. Boundary-scan Cell for Bi-directional Port Pin with Pull-up Function.
DQ DQ
G
0
1
0
1
DQ DQ
G
0
1
0
1
0
1
0
1
DQ DQ
G
0
1
Port Pin (PXn)
VccEXTESTTo Next CellShiftDR
Output Control (OC)
Pullup Enable (PUE)
Output Data (OD)
Input Data (ID)
From Last Cell UpdateDRClockDR
FF2 LD2
FF1 LD1
LD0FF0
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Figure 25-4. General Port Pin Schematic Diagram
25.6.2 Scanning the RESET Pin
The RESET pin accepts 5V active low logic for standard reset operation, and 12V active high
logic for High Voltage Parallel programming. An observe-only cell as shown in Figure 25-5 is
inserted both for the 5V reset signal; RSTT, and the 12V reset signal; RSTHV.
Figure 25-5. Observe-only Cell
CLK
RPx
RDx
WDx
PUD
SYNCHRONIZER
WDx: WRITE DDRx
WRx: WRITE PORTx
RRx: READ PORTx REGISTER
WPx: WRITE PINx REGISTER
PUD: PULLUP DISABLE
CLK : I/O CLOCK
RDx: READ DDRx
D
L
Q
Q
RESET
Q
Q
D
Q
QD
CLR
DDxn
PINxn
DATA B U S
SLEEP
SLEEP: SLEEP CONTROL
Pxn
I/O
I/O
See Boundary-scan
Description for Details!
PUExn
OCxn
ODxn
IDxn
PUExn: PULLUP ENABLE for pin Pxn
OCxn: OUTPUT CONTROL for pin Pxn
ODxn: OUTPUT DATA to pin Pxn
IDxn: INPUT DATA from pin Pxn RPx: READ PORTx PIN
RRx
RESET
Q
QD
CLR
PORTxn
WPx
0
1
WRx
0
1
DQ
From
Previous
Cell
ClockDR
ShiftDR
To
Next
Cell
From System Pin To System Logic
FF1
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25.6.3 Scanning the Clock Pins
The AVR devices have many clock options selectable by fuses. These are: Internal RC Oscilla-
tor, External Clock, (High Frequency) Crystal Oscillator, Low-frequency Crystal Oscillator, and
Ceramic Resonator.
Figure 25-6 shows how each Oscillator with external connection is supported in the scan chain.
The Enable signal is supported with a general Boundary-scan cell, while the Oscillator/clock out-
put is attached to an observe-only cell. In addition to the main clock, the timer Oscillator is
scanned in the same way. The output from the internal RC Oscillator is not scanned, as this
Oscillator does not have external connections.
Figure 25-6. Boundary-scan Cells for Oscillators and Clock Options
Table 25-3 summaries the scan registers for the external clock pin XTAL1, oscillators with
XTAL1/XTAL2 connections as well as 32kHz Timer Oscillator.
Notes: 1. Do not enable more than one clock source as main clock at a time.
2. Scanning an Oscillator output gives unpredictable results as there is a frequency drift between
the internal Oscillator and the JTAG TCK clock. If possible, scanning an external clock is
preferred.
3. The clock configuration is programmed by fuses. As a fuse is not changed run-time, the clock
configuration is considered fixed for a given application. The user is advised to scan the same
clock option as to be used in the final system. The enable signals are supported in the scan
chain because the system logic can disable clock options in sleep modes, thereby disconnect-
ing the Oscillator pins from the scan path if not provided.
Table 25-3. Scan Signals for the Oscillator(1)(2)(3)
Enable Signal Scanned Clock Line Clock Option
Scanned Clock
Line when not
Used
EXTCLKENEXTCLK (XTAL1) External Clock 0
OSCONOSCCK External Crystal
External Ceramic Resonator
1
OSC32ENOSC32CK Low Freq. External Crystal 1
0
1
DQ
From
Previous
Cell
ClockDR
ShiftDR
To
Next
Cell
To System Logic
FF1
0
1
DQ DQ
G
0
1
From
Previous
Cell
ClockDR UpdateDR
ShiftDR
To
Next
Cell EXTEST
From Digital Logic
XTAL1/TOSC1 XTAL2/TOSC2
Oscillator
ENABLE OUTPUT
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25.6.4 Scanning the Analog Comparator
The relevant Comparator signals regarding Boundary-scan are shown in Figure 25-7. The
Boundary-scan cell from Figure 25-8 is attached to each of these signals. The signals are
described in Table 25-4.
The Comparator need not be used for pure connectivity testing, since all analog inputs are
shared with a digital port pin as well.
Figure 25-7. Analog Comparator
Figure 25-8. General Boundary-scan cell Used for Signals for Comparator and ADC
ACBG
BANDGAP
REFERENCE
ADC MULTIPLEXER
OUTPUT
ACME
AC_IDLE
ACO
ADCEN
ACD
0
1
DQ DQ
G
0
1
From
Previous
Cell
ClockDR UpdateDR
ShiftDR
To
Next
Cell EXTEST
To Analog Circuitry/
To Digital Logic
From Digital Logic/
From Analog Ciruitry
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25.6.5 Scanning the ADC
Figure 25-9 shows a block diagram of the ADC with all relevant control and observe signals. The
Boundary-scan cell from Figure 25-5 is attached to each of these signals. The ADC need not be
used for pure connectivity testing, since all analog inputs are shared with a digital port pin as
well.
Figure 25-9. Analog to Digital Converter
The signals are described briefly in Table 25-5.
Table 25-4. Boundary-scan Signals for the Analog Comparator
Signal
Name
Direction as
Seen from the
Comparator Description
Recommended
Input when Not
in Use
Output Values when
Recommended
Inputs are Used
AC_IDLE input Turns off Analog
Comparator when
true
1 Depends upon µC
code being executed
ACO output Analog
Comparator Output
Will become
input to µC code
being executed
0
ACME input Uses output signal
from ADC mux
when true
0 Depends upon µC
code being executed
ACBG input Bandgap
Reference enable
0 Depends upon µC
code being executed
10-bit DAC +
-
AREF
PRECH
DACOUT
COMP
MUXEN_7
ADC_7
MUXEN_6
ADC_6
MUXEN_5
ADC_5
MUXEN_4
ADC_4
MUXEN_3
ADC_3
MUXEN_2
ADC_2
MUXEN_1
ADC_1
MUXEN_0
ADC_0
NEGSEL_2
ADC_2
NEGSEL_1
ADC_1
NEGSEL_0
ADC_0
EXTCH
+
-
1x
ST
ACLK
AMPEN
1.11V
ref
IREFEN
AREF
VCCREN
DAC_9..0
ADCEN
HOLD
PRECH
GNDEN
PASSEN
COMP
SCTEST ADCBGEN
To Comparator
1.22V
ref
ACTEN
AREF
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Table 25-5. Boundary-scan Signals for the ADC(1)
Signal Name
Direction as seen
from the ADC Description
Recommended
Input when not
in use
Output Values when
recommended inputs are used,
and CPU is not using the ADC
COMP Output Comparator Output 0 0
ACLK Input Clock signal to differential amplifier
implemented as Switch-cap filters
00
ACTENInput Enable path from differential amplifier to
the comparator
00
ADCBGENInput Enable Band-gap reference as negative
input to comparator
00
ADCENInput Power-on signal to the ADC 0 0
AMPENInput Power-on signal to the differential amplifier 0 0
DAC_9 Input Bit 9 of digital value to DAC 1 1
DAC_8Input Bit 8 of digital value to DAC 0 0
DAC_7 Input Bit 7 of digital value to DAC 0 0
DAC_6 Input Bit 6 of digital value to DAC 0 0
DAC_5 Input Bit 5 of digital value to DAC 0 0
DAC_4 Input Bit 4 of digital value to DAC 0 0
DAC_3 Input Bit 3 of digital value to DAC 0 0
DAC_2 Input Bit 2 of digital value to DAC 0 0
DAC_1 Input Bit 1 of digital value to DAC 0 0
DAC_0 Input Bit 0 of digital value to DAC 0 0
EXTCH Input Connect ADC channels 0 - 3 to by-pass
path around differential amplifier
11
GNDENInput Ground the negative input to comparator
when true
00
HOLD Input Sample & Hold signal. Sample analog
signal when low. Hold signal when high. If
differential amplifier are used, this signal
must go active when ACLK is high.
11
IREFENInput Enables Band-gap reference as AREF
signal to DAC
00
MUXEN_7 Input Input Mux bit 7 0 0
MUXEN_6 Input Input Mux bit 6 0 0
MUXEN_5 Input Input Mux bit 5 0 0
MUXEN_4 Input Input Mux bit 4 0 0
MUXEN_3 Input Input Mux bit 3 0 0
MUXEN_2 Input Input Mux bit 2 0 0
MUXEN_1 Input Input Mux bit 1 0 0
MUXEN_0 Input Input Mux bit 0 1 1
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Notes: 1. Incorrect setting of the switches in Figure 25-9 will make signal contention and may damage the part. There are several input
choices to the S&H circuitry on the negative input of the output comparator in Figure 25-9. Make sure only one path is
selected from either one ADC pin, Bandgap reference source, or Ground.
If the ADC is not to be used during scan, the recommended input values from Table 25-5 should
be used. The user is recommended not to use the differential amplifier during scan. Switch-Cap
based differential amplifier require fast operation and accurate timing which is difficult to obtain
when used in a scan chain. Details concerning operations of the differential amplifier is therefore
not provided.
The AVR ADC is based on the analog circuitry shown in Figure 25-9 with a successive approxi-
mation algorithm implemented in the digital logic. When used in Boundary-scan, the problem is
usually to ensure that an applied analog voltage is measured within some limits. This can easily
be done without running a successive approximation algorithm: apply the lower limit on the digi-
tal DAC[9:0] lines, make sure the output from the comparator is low, then apply the upper limit
on the digital DAC[9:0] lines, and verify the output from the comparator to be high.
The ADC need not be used for pure connectivity testing, since all analog inputs are shared with
a digital port pin as well.
When using the ADC, remember the following
• The port pin for the ADC channel in use must be configured to be an input with pull-up
disabled to avoid signal contention.
•In Normal mode, a dummy conversion (consisting of 10 comparisons) is performed when
enabling the ADC. The user is advised to wait at least 200ns after enabling the ADC before
controlling/observing any ADC signal, or perform a dummy conversion before using the first
result.
• The DAC values must be stable at the midpoint value 0x200 when having the HOLD signal
low (Sample mode).
NEGSEL_2 Input Input Mux for negative input for differential
signal, bit 2
00
NEGSEL_1 Input Input Mux for negative input for differential
signal, bit 1
00
NEGSEL_0 Input Input Mux for negative input for differential
signal, bit 0
00
PASSENInput Enable pass-gate of differential amplifier. 1 1
PRECH Input Precharge output latch of comparator.
(Active low)
11
SCTEST Input Switch-cap TEST enable. Output from
differential amplifier send out to Port Pin
having ADC_4
00
ST Input Output of differential amplifier will settle
faster if this signal is high first two ACLK
periods after AMPEN goes high.
00
VCCRENInput Selects Vcc as the ACC reference voltage. 0 0
Table 25-5. Boundary-scan Signals for the ADC(1) (Continued)
Signal Name
Direction as seen
from the ADC Description
Recommended
Input when not
in use
Output Values when
recommended inputs are used,
and CPU is not using the ADC
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As an example, consider the task of verifying a 1.5V ± 5% input signal at ADC channel 3 when
the power supply is 5.0V and AREF is externally connected to VCC.
The recommended values from Table 25-5 are used unless other values are given in the algo-
rithm in Table 25-6. Only the DAC and port pin values of the Scan Chain are shown. The column
“Actions” describes what JTAG instruction to be used before filling the Boundary-scan Register
with the succeeding columns. The verification should be done on the data scanned out when
scanning in the data on the same row in the table.
Using this algorithm, the timing constraint on the HOLD signal constrains the TCK clock fre-
quency. As the algorithm keeps HOLD high for five steps, the TCK clock frequency has to be at
least five times the number of scan bits divided by the maximum hold time, thold,max
Table 25-6. Algorithm for Using the ADC
Step Actions ADCEN DAC MUXEN HOLD PRECH
PA3 .
Data
PA3.
Control
PA3.
Pull-
up_
Enable
1SAMPLE_
PRELOAD 1 0x200 0x081100 0
2 EXTEST 1 0x200 0x080100 0
31 0x200 0x081100 0
41 0x123 0x081100 0
51 0x123 0x081000 0
6
Verify the
COMP bit
scanned
out to be 0
1 0x200 0x081100 0
71 0x200 0x080100 0
81 0x200 0x081100 0
91 0x143 0x081100 0
10 1 0x143 0x081000 0
11
Verify the
COMP bit
scanned
out to be 1
1 0x200 0x081100 0
The lower limit is: 1024 1.5V0,95 5V⁄⋅⋅ 291 0x123==
The upper limit is: 1024 1.5V1.05 5V⁄⋅⋅ 323 0x143==
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25.7 ATmega329/3290/649/6490 Boundary-scan Order
Table 25-7 and Table 25-8 shows the Scan order between TDI and TDO when the Boundary-
scan chain is selected as data path. Bit 0 is the LSB; the first bit scanned in, and the first bit
scanned out. The scan order follows the pin-out order as far as possible. Therefore, the bits of
Port A is scanned in the opposite bit order of the other ports. Exceptions from the rules are the
Scan chains for the analog circuits, which constitute the most significant bits of the scan chain
regardless of which physical pin they are connected to. In Figure 25-3, PXn. Data corresponds
to FF0, PXn. Control corresponds to FF1, and PXn. Pull-up_enable corresponds to FF2. Bit 4, 5,
6 and 7 of Port F is not in the scan chain, since these pins constitute the TAP pins when the
JTAG is enabled.
Table 25-7. ATmega329/649 Boundary-scan Order, 64-pin
Bit Number Signal Name Module
197 AC_IDLE Comparator
196 ACO
195 ACME
194 AINBG
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193 COMP ADC
192 ACLK
191 ACTEN
190 PRIVATE_SIGNAL1(1)
189 ADCBGEN
188 ADCEN
187AMPEN
186DAC_9
185DAC_8
184DAC_7
183DAC_6
182DAC_5
181DAC_4
180DAC_3
179 DAC_2
178DAC_1
177 DAC_0
176 EXTCH
175 GNDEN
174 HOLD
173 IREFEN
172 MUXEN_7
171 MUXEN_6
170 MUXEN_5
169 MUXEN_4
168MUXEN_3
167 MUXEN_2
166 MUXEN_1
165 MUXEN_0
164 NEGSEL_2
163 NEGSEL_1
162 NEGSEL_0
161 PASSEN
160 PRECH
159 ST
158VCCREN
Table 25-7. ATmega329/649 Boundary-scan Order, 64-pin (Continued)
Bit Number Signal Name Module
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157 PE0.Data Port E
156 PE0.Control
155 PE0.Pull-up_Enable
154 PE1.Data
153 PE1.Control
152 PE1.Pull-up_Enable
151 PE2.Data
150 PE2.Control
149 PE2.Pull-up_Enable
148PE3.Data
147 PE3.Control
146 PE3.Pull-up_Enable
145 PE4.Data
144 PE4.Control
143 PE4.Pull-up_Enable
142 PE5.Data
141 PE5.Control
140 PE5.Pull-up_Enable
139 PE6.Data
138PE6.Control
137 PE6.Pull-up_Enable
136 PE7.Data
135 PE7.Control
134 PE7.Pull-up_Enable
Table 25-7. ATmega329/649 Boundary-scan Order, 64-pin (Continued)
Bit Number Signal Name Module
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133 PB0.Data Port B
132 PB0.Control
131 PB0.Pull-up_Enable
130 PB1.Data
129 PB1.Control
128PB1.Pull-up_Enable
127 PB2.Data
126 PB2.Control
125 PB2.Pull-up_Enable
124 PB3.Data
123 PB3.Control
122 PB3.Pull-up_Enable
121 PB4.Data
120 PB4.Control
119 PB4.Pull-up_Enable
118PB5.Data
117 PB5.Control
116 PB5.Pull-up_Enable
115 PB6.Data
114 PB6.Control
113 PB6.Pull-up_Enable
112 PB7.Data
111 PB7.Control
110 PB7.Pull-up_Enable
109 PG3.Data Port G
108PG3.Control
107 PG3.Pull-up_Enable
106 PG4.Data
105 PG4.Control
104 PG4.Pull-up_Enable
103 PG5 (Observe Only)
102 RSTT Reset Logic
(Observe-only)
101 RSTHV
Table 25-7. ATmega329/649 Boundary-scan Order, 64-pin (Continued)
Bit Number Signal Name Module
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100 EXTCLKENEnable signals for main Clock/Oscillators
99 OSCON
98RCOSCEN
97 OSC32EN
96 EXTCLK (XTAL1) Clock input and Oscillators for the main
clock
(Observe-only)
95 OSCCK
94 RCCK
93 OSC32CK
92 PD0.Data Port D
91 PD0.Control
90 PD0.Pull-up_Enable
89PD1.Data
88 PD1.Control
87 PD1.Pull-up_Enable
86PD2.Data
85 PD2.Control
84 PD2.Pull-up_Enable
83PD3.Data
82 PD3.Control
81 PD3.Pull-up_Enable
80PD4.Data
79 PD4.Control
78PD4.Pull-up_Enable
77 PD5.Data
76 PD5.Control
75 PD5.Pull-up_Enable
74 PD6.Data
73 PD6.Control
72 PD6.Pull-up_Enable
71 PD7.Data
70 PD7.Control
69 PD7.Pull-up_Enable
68PG0.Data Port G
67 PG0.Control
66 PG0.Pull-up_Enable
65 PG1.Data
Table 25-7. ATmega329/649 Boundary-scan Order, 64-pin (Continued)
Bit Number Signal Name Module
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64 PG1.Control
63 PG1.Pull-up_Enable
62 PC0.Data Port C
61 PC0.Control
60 PC0.Pull-up_Enable
59 PC1.Data
58PC1.Control
57 PC1.Pull-up_Enable
56 PC2.Data
55 PC2.Control
54 PC2.Pull-up_Enable
53 PC3.Data
52 PC3.Control
51 PC3.Pull-up_Enable
50 PC4.Data
49 PC4.Control
48PC4.Pull-up_Enable
47 PC5.Data
46 PC5.Control
45 PC5.Pull-up_Enable
44 PC6.Data
43 PC6.Control
42 PC6.Pull-up_Enable
41 PC7.Data
40 PC7.Control
39 PC7.Pull-up_Enable
38PG2.Data Port G
37 PG2.Control
36 PG2.Pull-up_Enable
35 PA7.Data Port A
34 PA7.Control
33 PA7.Pull-up_Enable
32 PA6.Data
31 PA6.Control
30 PA6.Pull-up_Enable
29 PA5.Data
Table 25-7. ATmega329/649 Boundary-scan Order, 64-pin (Continued)
Bit Number Signal Name Module
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Note: 1. PRIVATE_SIGNAL1 should always be scanned in as zero.
28PA5.Control
27 PA5.Pull-up_Enable
26 PA4.Data
25 PA4.Control
24 PA4.Pull-up_Enable
23 PA3.Data
22 PA3.Control
21 PA3.Pull-up_Enable
20 PA2.Data
19 PA2.Control
18PA2.Pull-up_Enable
17 PA1.Data
16 PA1.Control
15 PA1.Pull-up_Enable
14 PA0.Data
13 PA0.Control
12 PA0.Pull-up_Enable
11 PF3.Data Port F
10 PF3.Control
9 PF3.Pull-up_Enable
8PF2.Data
7 PF2.Control
6 PF2.Pull-up_Enable
5PF1.Data
4 PF1.Control
3 PF1.Pull-up_Enable
2PF0.Data
1 PF0.Control
0 PF0.Pull-up_Enable
Table 25-7. ATmega329/649 Boundary-scan Order, 64-pin (Continued)
Bit Number Signal Name Module
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Table 25-8. ATmega3290/6490 Boundary-scan Order, 100-pin
Bit Number Signal Name Module
242 AC_IDLE Comparator
241 ACO
240 ACME
239 AINBG
238COMP ADC
237 ACLK
236 ACTEN
235 PRIVATE_SIGNAL1(1)
234 ADCBGEN
233 ADCEN
232 AMPEN
231 DAC_9
230 DAC_8
229 DAC_7
228DAC_6
227 DAC_5
226 DAC_4
225 DAC_3
224 DAC_2
223 DAC_1
222 DAC_0
221 EXTCH
220 GNDEN
219 HOLD
218IREFEN
217 MUXEN_7
216 MUXEN_6
215 MUXEN_5
214 MUXEN_4
213 MUXEN_3
212 MUXEN_2
211 MUXEN_1
210 MUXEN_0
209 NEGSEL_2
208NEGSEL_1
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207 NEGSEL_0
206 PASSEN
205 PRECH
204 ST
203 VCCREN
202 PE0.Data Port E
201 PE0.Control
200 PE0.Pull-up_Enable
199 PE1.Data
198PE1.Control
197 PE1.Pull-up_Enable
196 PE2.Data
195 PE2.Control
194 PE2.Pull-up_Enable
193 PE3.Data
192 PE3.Control
191 PE3.Pull-up_Enable
190 PE4.Data
189 PE4.Control
188 PE4.Pull-up_Enable
187 PE5.Data
186 PE5.Control
185 PE5.Pull-up_Enable
184 PE6.Data
183 PE6.Control
182 PE6.Pull-up_Enable
181 PE7.Data
180 PE7.Control
179 PE7.Pull-up_Enable
178PJ0.Data Port J
177 PJ0.Control
176 PJ0.Pull-up_Enable
175 PJ1.Data
174 PJ1.Control
173 PJ1.Pull-up_Enable
172 PB0.Data Port B
Table 25-8. ATmega3290/6490 Boundary-scan Order, 100-pin (Continued)
Bit Number Signal Name Module
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171 PB0.Control
170 PB0.Pull-up_Enable
169 PB1.Data
168PB1.Control
167 PB1.Pull-up_Enable
166 PB2.Data
165 PB2.Control
164 PB2.Pull-up_Enable
163 PB3.Data
162 PB3.Control
161 PB3.Pull-up_Enable
160 PB4.Data
159 PB4.Control
158PB4.Pull-up_Enable
157 PB5.Data
156 PB5.Control
155 PB5.Pull-up_Enable
154 PB6.Data
153 PB6.Control
152 PB6.Pull-up_Enable
151 PB7.Data
150 PB7.Control
149 PB7.Pull-up_Enable
148PG3.Data Port G
147 PG3.Control
146 PG3.Pull-up_Enable
145 PG4.Data
144 PG4.Control
143 PG4.Pull-up_Enable
142 PG5 (Observe Only)
141 RSTT Reset Logic
(Observe-only)
140 RSTHV
139 EXTCLKENEnable signals for main Clock/Oscillators
138OSCON
137 RCOSCEN
136 OSC32EN
Table 25-8. ATmega3290/6490 Boundary-scan Order, 100-pin (Continued)
Bit Number Signal Name Module
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135 EXTCLK (XTAL1) Clock input and Oscillators for the main
clock
(Observe-only)
134 OSCCK
133 RCCK
132 OSC32CK
131 PJ2.Data Port J
130 PJ2.Control
129 PJ2.Pull-up_Enable
128PJ3.Data
127 PJ3.Control
126 PJ3.Pull-up_Enable
125 PJ4.Data
124 PJ4.Control
123 PJ4.Pull-up_Enable
122 PJ5.Data
121 PJ5.Control
120 PJ5.Pull-up_Enable
119 PJ6.Data
118PJ6.Control
117 PJ6.Pull-up_Enable
116 PD0.Data Port D
115 PD0.Control
114 PD0.Pull-up_Enable
113 PD1.Data
112 PD1.Control
111 PD1.Pull-up_Enable
110 PD2.Data
109 PD2.Control
108PD2.Pull-up_Enable
107 PD3.Data
106 PD3.Control
105 PD3.Pull-up_Enable
104 PD4.Data
103 PD4.Control
102 PD4.Pull-up_Enable
101 PD5.Data
100 PD5.Control
Table 25-8. ATmega3290/6490 Boundary-scan Order, 100-pin (Continued)
Bit Number Signal Name Module
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99 PD5.Pull-up_Enable
98PD6.Data
97 PD6.Control
96 PD6.Pull-up_Enable
95 PD7.Data
94 PD7.Control
93 PD7.Pull-up_Enable
92 PG0.Data Port G
91 PG0.Control
90 PG0.Pull-up_Enable
89PG1.Data
88 PG1.Control
87 PG1.Pull-up_Enable
86 PC0.Data Port C
85 PC0.Control
84 PC0.Pull-up_Enable
83PC1.Data
82 PC1.Control
81 PC1.Pull-up_Enable
80PC2.Data
79 PC2.Control
78PC2.Pull-up_Enable
77 PC3.Data
76 PC3.Control
75 PC3.Pull-up_Enable
74 PC4.Data
73 PC4.Control
72 PC4.Pull-up_Enable
71 PC5.Data
70 PC5.Control
69 PC5.Pull-up_Enable
68PH0.Data Port H
67 PH0.Control
66 PH0.Pull-up_Enable
65 PH1.Data
64 PH1.Control
Table 25-8. ATmega3290/6490 Boundary-scan Order, 100-pin (Continued)
Bit Number Signal Name Module
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63 PH1.Pull-up_Enable
62 PH2.Data
61 PH2.Control
60 PH2.Pull-up_Enable
59 PH3.Data
58PH3.Control
57 PH3.Pull-up_Enable
56 PC6.Data Port C
55 PC6.Control
54 PC6.Pull-up_Enable
53 PC7.Data
52 PC7.Control
51 PC7.Pull-up_Enable
50 PG2.Data Port G
49 PG2.Control
48PG2.Pull-up_Enable
47 PA7.Data Port A
46 PA7.Control
45 PA7.Pull-up_Enable
44 PA6.Data
43 PA6.Control
42 PA6.Pull-up_Enable
41 PA5.Data
40 PA5.Control
39 PA5.Pull-up_Enable
38PA 4 . D at a
37 PA4.Control
36 PA4.Pull-up_Enable
35 PA3.Data
34 PA3.Control
33 PA3.Pull-up_Enable
32 PA2.Data
31 PA2.Control
30 PA2.Pull-up_Enable
29 PA1.Data
28PA1.Control
Table 25-8. ATmega3290/6490 Boundary-scan Order, 100-pin (Continued)
Bit Number Signal Name Module
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Note: 1. PRIVATE_SIGNAL1 should always be scanned in as zero.
25.8 Boundary-scan Description Language Files
Boundary-scan Description Language (BSDL) files describe Boundary-scan capable devices in
a standard format used by automated test-generation software. The order and function of bits in
the Boundary-scan Data Register are included in this description. A BSDL file for
ATmega329/3290/649/6490 is available.
27 PA1.Pull-up_Enable
26 PA0.Data
25 PA0.Control
24 PA0.Pull-up_Enable
23 PH4.Data Port H
22 PH4.Control
21 PH4.Pull-up_Enable
20 PH5.Data
19 PH5.Control
18PH5.Pull-up_Enable
17 PH6.Data
16 PH6.Control
15 PH6.Pull-up_Enable
14 PH7.Data
13 PH7.Control
12 PH7.Pull-up_Enable
11 PF3.Data Port F
10 PF3.Control
9 PF3.Pull-up_Enable
8PF2.Data
7 PF2.Control
6 PF2.Pull-up_Enable
5PF1.Data
4 PF1.Control
3 PF1.Pull-up_Enable
2PF0.Data
1 PF0.Control
0 PF0.Pull-up_Enable
Table 25-8. ATmega3290/6490 Boundary-scan Order, 100-pin (Continued)
Bit Number Signal Name Module
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26. Boot Loader Support – Read-While-Write Self-Programming
The Boot Loader Support provides a real Read-While-Write Self-Programming mechanism for
downloading and uploading program code by the MCU itself. This feature allows flexible applica-
tion software updates controlled by the MCU using a Flash-resident Boot Loader program. The
Boot Loader program can use any available data interface and associated protocol to read code
and write (program) that code into the Flash memory, or read the code from the program mem-
ory. The program code within the Boot Loader section has the capability to write into the entire
Flash, including the Boot Loader memory. The Boot Loader can thus even modify itself, and it
can also erase itself from the code if the feature is not needed anymore. The size of the Boot
Loader memory is configurable with fuses and the Boot Loader has two separate sets of Boot
Lock bits which can be set independently. This gives the user a unique flexibility to select differ-
ent levels of protection.
26.1 Features
•Read-While-Write Self-Programming
•Flexible Boot Memory Size
•High Security (Separate Boot Lock Bits for a Flexible Protection)
•Separate Fuse to Select Reset Vector
•Optimized Page(1) Size
•Code Efficient Algorithm
•Efficient Read-Modify-Write Support
Note: 1. A page is a section in the Flash consisting of several bytes (see Table 27-10 on page 298)
used during programming. The page organization does not affect normal operation.
26.2 Application and Boot Loader Flash Sections
The Flash memory is organized in two main sections, the Application section and the Boot
Loader section (see Figure 26-2). The size of the different sections is configured by the
BOOTSZ Fuses as shown in Table 26-6 on page 290 and Figure 26-2. These two sections can
have different level of protection since they have different sets of Lock bits.
26.2.1 Application Section
The Application section is the section of the Flash that is used for storing the application code.
The protection level for the Application section can be selected by the application Boot Lock bits
(Boot Lock bits 0), see Table 26-2 on page 282. The Application section can never store any
Boot Loader code since the SPM instruction is disabled when executed from the Application
section.
26.2.2 BLS – Boot Loader Section
While the Application section is used for storing the application code, the The Boot Loader soft-
ware must be located in the BLS since the SPM instruction can initiate a programming when
executing from the BLS only. The SPM instruction can access the entire Flash, including the
BLS itself. The protection level for the Boot Loader section can be selected by the Boot Loader
Lock bits (Boot Lock bits 1), see Table 26-3 on page 282.
26.3 Read-While-Write and No Read-While-Write Flash Sections
Whether the CPU supports Read-While-Write or if the CPU is halted during a Boot Loader soft-
ware update is dependent on which address that is being programmed. In addition to the two
sections that are configurable by the BOOTSZ Fuses as described above, the Flash is also
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divided into two fixed sections, the Read-While-Write (RWW) section and the No Read-While-
Write (NRWW) section. The limit between the RWW- and NRWW sections is given in Table 26-
7 on page 290 and Figure 26-2 on page 281. The main difference between the two sections is:
• When erasing or writing a page located inside the RWW section, the NRWW section can be
read during the operation.
• When erasing or writing a page located inside the NRWW section, the CPU is halted during
the entire operation.
Note that the user software can never read any code that is located inside the RWW section dur-
ing a Boot Loader software operation. The syntax “Read-While-Write section” refers to which
section that is being programmed (erased or written), not which section that actually is being
read during a Boot Loader software update.
26.3.1 RWW – Read-While-Write Section
If a Boot Loader software update is programming a page inside the RWW section, it is possible
to read code from the Flash, but only code that is located in the NRWW section. During an on-
going programming, the software must ensure that the RWW section never is being read. If the
user software is trying to read code that is located inside the RWW section (i.e., by a
call/jmp/lpm or an interrupt) during programming, the software might end up in an unknown
state. To avoid this, the interrupts should either be disabled or moved to the Boot Loader sec-
tion. The Boot Loader section is always located in the NRWW section. The RWW Section Busy
bit (RWWSB) in the Store Program Memory Control and Status Register (SPMCSR) will be read
as logical one as long as the RWW section is blocked for reading. After a programming is com-
pleted, the RWWSB must be cleared by software before reading code located in the RWW
section. See “SPMCSR – Store Program Memory Control and Status Register” on page 291. for
details on how to clear RWWSB.
26.3.2 NRWW – No Read-While-Write Section
The code located in the NRWW section can be read when the Boot Loader software is updating
a page in the RWW section. When the Boot Loader code updates the NRWW section, the CPU
is halted during the entire Page Erase or Page Write operation.
Table 26-1. Read-While-Write Features
Which Section does the Z-
pointer Address During the
Programming?
Which Section Can
be Read During
Programming?
Is the CPU
Halted?
Read-While-Write
Supported?
RWW Section NRWW Section NoYes
NRWW Section None Yes No
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Figure 26-1. Read-While-Write vs. No Read-While-Write
Read-While-Write
(RWW) Section
No Read-While-Write
(NRWW) Section
Z-pointer
Addresses RWW
Section
Z-pointer
Addresses NRWW
Section
CPU is Halted
During the Operation
Code Located in
NRWW Section
Can be Read During
the Operation
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Figure 26-2. Memory Sections
Note: 1. The parameters in the figure above are given in Table 26-6 on page 290.
26.4 Boot Loader Lock Bits
If no Boot Loader capability is needed, the entire Flash is available for application code. The
Boot Loader has two separate sets of Boot Lock bits which can be set independently. This gives
the user a unique flexibility to select different levels of protection.
The user can select:
• To protect the entire Flash from a software update by the MCU.
• To protect only the Boot Loader Flash section from a software update by the MCU.
• To protect only the Application Flash section from a software update by the MCU.
• Allow software update in the entire Flash.
See Table 26-2 and Table 26-3 for further details. The Boot Lock bits and general Lock bits can
be set in software and in Serial or Parallel Programming mode, but they can be cleared by a
Chip Erase command only. The general Write Lock (Lock Bit mode 2) does not control the pro-
gramming of the Flash memory by SPM instruction. Similarly, the general Read/Write Lock
(Lock Bit mode 1) does not control reading nor writing by LPM/SPM, if it is attempted.
0x0000
Flashend
Program Memory
BOOTSZ = '11'
Application Flash Section
Boot Loader Flash Section
Flashend
Program Memory
BOOTSZ = '10'
0x0000
Program Memory
BOOTSZ = '01'
Program Memory
BOOTSZ = '00'
Application Flash Section
Boot Loader Flash Section
0x0000
Flashend
Application Flash Section
Flashend
End RWW
Start NRWW
Application Flash Section
Boot Loader Flash Section
Boot Loader Flash Section
End RWW
Start NRWW
End RWW
Start NRWW
0x0000
End RWW, End Application
Start NRWW, Start Boot Loader
Application Flash SectionApplication Flash Section
Application Flash Section
Read-While-Write SectionNo Read-While-Write Section Read-While-Write SectionNo Read-While-Write Section
Read-While-Write SectionNo Read-While-Write SectionRead-While-Write SectionNo Read-While-Write Section
End Application
Start Boot Loader
End Application
Start Boot Loader
End Application
Start Boot Loader
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Note: 1. “1” means unprogrammed, “0” means programmed
Note: 1. “1” means unprogrammed, “0” means programmed
26.5 Entering the Boot Loader Program
Entering the Boot Loader takes place by a jump or call from the application program. This may
be initiated by a trigger such as a command received via USART, or SPI interface. Alternatively,
the Boot Reset Fuse can be programmed so that the Reset Vector is pointing to the Boot Flash
start address after a reset. In this case, the Boot Loader is started after a reset. After the applica-
tion code is loaded, the program can start executing the application code. Note that the fuses
cannot be changed by the MCU itself. This means that once the Boot Reset Fuse is pro-
grammed, the Reset Vector will always point to the Boot Loader Reset and the fuse can only be
changed through the serial or parallel programming interface.
Note: 1. “1” means unprogrammed, “0” means programmed
Table 26-2. Boot Lock Bit0 Protection Modes (Application Section)(1)
BLB0
Mode BLB02 BLB01 Protection
11 1No restrictions for SPM or LPM accessing the Application section.
2 1 0 SPM is not allowed to write to the Application section.
3 0 0 SPM is not allowed to write to the Application section, and LPM executing
from the Boot Loader section is not allowed to read from the Application
section. If Interrupt Vectors are placed in the Boot Loader section,
interrupts are disabled while executing from the Application section.
4 0 1 LPM executing from the Boot Loader section is not allowed to read from
the Application section. If Interrupt Vectors are placed in the Boot Loader
section, interrupts are disabled while executing from the Application
section.
Table 26-3. Boot Lock Bit1 Protection Modes (Boot Loader Section)(1)
BLB1
Mode BLB12 BLB11 Protection
11 1No restrictions for SPM or LPM accessing the Boot Loader section.
2 1 0 SPM is not allowed to write to the Boot Loader section.
3 0 0 SPM is not allowed to write to the Boot Loader section, and LPM
executing from the Application section is not allowed to read from the
Boot Loader section. If Interrupt Vectors are placed in the Application
section, interrupts are disabled while executing from the Boot Loader
section.
4 0 1 LPM executing from the Application section is not allowed to read from
the Boot Loader section. If Interrupt Vectors are placed in the Application
section, interrupts are disabled while executing from the Boot Loader
section.
Table 26-4. Boot Reset Fuse(1)
BOOTRST Reset Address
1 Reset Vector = Application Reset (address 0x0000)
0 Reset Vector = Boot Loader Reset (see Table 26-6 on page 290)
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26.6 Addressing the Flash During Self-Programming
The Z-pointer is used to address the SPM commands.
Since the Flash is organized in pages (see Table 27-10 on page 298), 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 26-3. Note that the Page Erase and Page Write operations are
addressed independently. Therefore it is of major importance that the Boot Loader software
addresses the same page in both the Page Erase and Page Write operation. Once a program-
ming operation is initiated, the address is latched and the Z-pointer can be used for other
operations.
The only SPM operation that does not use the Z-pointer is Setting the Boot Loader Lock bits.
The content of the Z-pointer is ignored and will have no effect on the operation. The LPM
instruction does also use the Z-pointer to store the address. Since this instruction addresses the
Flash byte-by-byte, also the LSB (bit Z0) of the Z-pointer is used.
Figure 26-3. Addressing the Flash During SPM(1)
Note: 1. The different variables used in Figure 26-3 are listed in Table 26-8 on page 290.
2. PCPAGE and PCWORD are listed in Table 27-10 on page 298.
26.7 Self-Programming the Flash
The program memory is updated in a page by page fashion. Before programming a page with
the data stored in the temporary page buffer, the page must be erased. The temporary page buf-
Bit 151413121110 9 8
ZH (R31) Z15 Z14 Z13 Z12 Z11 Z10 Z9 Z8
ZL (R30) Z7Z6Z5Z4Z3Z2Z1Z0
76543210
PROGRAM MEMORY
0115
Z - REGISTER
BIT
0
ZPAGEMSB
WORD ADDRESS
WITHIN A PAGE
PAGE ADDRESS
WITHIN THE FLASH
ZPCMSB
INSTRUCTION WORD
PA G E PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
PA G E
PCWORDPCPAGE
PCMSB PAGEMSB
PROGRAM
COUNTER
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fer is filled one word at a time using SPM and the buffer can be filled either before the Page
Erase command or between a Page Erase and a Page Write operation:
Alternative 1, fill the buffer before a Page Erase
• Fill temporary page buffer
• Perform a Page Erase
• Perform a Page Write
Alternative 2, fill the buffer after Page Erase
• Perform a Page Erase
• Fill temporary page buffer
• Perform a Page Write
If only a part of the page needs to be changed, the rest of the page must be stored (for example
in the temporary page buffer) before the erase, and then be rewritten. When using alternative 1,
the Boot Loader provides an effective Read-Modify-Write feature which allows the user software
to first read the page, do the necessary changes, and then write back the modified data. If alter-
native 2 is used, it is not possible to read the old data while loading since the page is already
erased. The temporary page buffer can be accessed in a random sequence. It is essential that
the page address used in both the Page Erase and Page Write operation is addressing the same
page. See “Simple Assembly Code Example for a Boot Loader” on page 288 for an assembly
code example.
26.7.1 Performing Page Erase by SPM
To execute Page Erase, set up the address in the Z-pointer, write “X0000011” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored.
The page address must be written to PCPAGE in the Z-register. Other bits in the Z-pointer will
be ignored during this operation.
• Page Erase to the RWW section: The NRWW section can be read during the Page Erase.
• Page Erase to the NRWW section: The CPU is halted during the operation.
26.7.2 Filling the Temporary Buffer (Page Loading)
To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write
“00000001” to SPMCSR and execute SPM within four clock cycles after writing SPMCSR. The
content of PCWORD in the Z-register is used to address the data in the temporary buffer. The
temporary buffer will auto-erase after a Page Write operation or by writing the RWWSRE bit in
SPMCSR. It is also erased after a system reset. Note that it is not possible to write more than
one time to each address without erasing the temporary buffer.
If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded will be
lost.
26.7.3 Performing a Page Write
To execute Page Write, set up the address in the Z-pointer, write “X0000101” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored.
The page address must be written to PCPAGE. Other bits in the Z-pointer must be written to
zero during this operation.
• Page Write to the RWW section: The NRWW section can be read during the Page Write.
• Page Write to the NRWW section: The CPU is halted during the operation.
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26.7.4 Using the SPM Interrupt
If the SPM interrupt is enabled, the SPM interrupt will generate a constant interrupt when the
SPMEN bit in SPMCSR is cleared. This means that the interrupt can be used instead of polling
the SPMCSR Register in software. When using the SPM interrupt, the Interrupt Vectors should
be moved to the BLS section to avoid that an interrupt is accessing the RWW section when it is
blocked for reading. How to move the interrupts is described in “Interrupts” on page 49.
26.7.5 Consideration While Updating BLS
Special care must be taken if the user allows the Boot Loader section to be updated by leaving
Boot Lock bit11 unprogrammed. An accidental write to the Boot Loader itself can corrupt the
entire Boot Loader, and further software updates might be impossible. If it is not necessary to
change the Boot Loader software itself, it is recommended to program the Boot Lock bit11 to
protect the Boot Loader software from any internal software changes.
26.7.6 Prevent Reading the RWW Section During Self-Programming
During Self-Programming (either Page Erase or Page Write), the RWW section is always
blocked for reading. The user software itself must prevent that this section is addressed during
the self programming operation. The RWWSB in the SPMCSR will be set as long as the RWW
section is busy. During Self-Programming the Interrupt Vector table should be moved to the BLS
as described in “Interrupts” on page 49, or the interrupts must be disabled. Before addressing
the RWW section after the programming is completed, the user software must clear the
RWWSB by writing the RWWSRE. See “Simple Assembly Code Example for a Boot Loader” on
page 288 for an example.
26.7.7 Setting the Boot Loader Lock Bits by SPM
To set the Boot Loader Lock bits and general Lock bits, write the desired data to R0, write
“X0001001” to SPMCSR and execute SPM within four clock cycles after writing SPMCSR.
See Table 26-2 and Table 26-3 for how the different settings of the Boot Loader bits affect the
Flash access.
If bits 5..0 in R0 are cleared (zero), the corresponding Lock bit will be programmed if an SPM
instruction is executed within four cycles after BLBSET and SPMEN are set in SPMCSR. The Z-
pointer is don’t care during this operation, but for future compatibility it is recommended to load
the Z-pointer with 0x0001 (same as used for reading the Lock bits). For future compatibility it is
also recommended to set bits 7, and 6 in R0 to “1” when writing the Lock bits. When program-
ming the Lock bits the entire Flash can be read during the operation.
26.7.8 EEPROM Write Prevents Writing to SPMCSR
Note that an EEPROM write operation will block all software programming to Flash. Reading the
Fuses and Lock bits from software will also be prevented during the EEPROM write operation. It
is recommended that the user checks the status bit (EEWE) in the EECR Register and verifies
that the bit is cleared before writing to the SPMCSR Register.
26.7.9 Reading the Fuse and Lock Bits from Software
It is possible to read both the Fuse and Lock bits from software. To read the Lock bits, load the
Z-pointer with 0x0001 and set the BLBSET and SPMEN bits in SPMCSR. When an LPM instruc-
tion is executed within three CPU cycles after the BLBSET and SPMEN bits are set in SPMCSR,
Bit 76543210
R0 1 1 BLB12 BLB11 BLB02 BLB01 LB2 LB1
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the value of the Lock bits will be loaded in the destination register. The BLBSET 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 BLB-
SET and SPMEN are cleared, LPM will work as described in the Instruction set Manual.
The algorithm for reading the Fuse Low byte is similar to the one described above for reading
the Lock bits. To read the Fuse Low byte, load the Z-pointer with 0x0000 and set the BLBSET
and SPMEN bits in SPMCSR. When an LPM instruction is executed within three cycles after the
BLBSET 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. Refer to Table 27-5 on page 295 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 instruc-
tion is executed within three cycles after the BLBSET 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.
Refer to Table 27-4 on page 295 for detailed description and mapping of the Fuse High byte.
When reading the Extended Fuse byte, load 0x0002 in the Z-pointer. When an LPM instruction
is executed within three cycles after the BLBSET and SPMEN bits are set in the SPMCSR, the
value of the Extended Fuse byte (EFB) will be loaded in the destination register as shown below.
Refer to Table 27-3 on page 294 for detailed description and mapping of the Extended Fuse
byte.
Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that are
unprogrammed, will be read as one.
26.7.10 Preventing Flash Corruption
During periods of low VCC, the Flash program can be corrupted because the supply voltage is
too low for the CPU and the Flash to operate properly. These issues are the same as for board
level systems using the Flash, and the same design solutions should be applied.
A Flash program corruption can be caused by two situations when the voltage is too low. First, a
regular write sequence to the Flash requires a minimum voltage to operate correctly. Secondly,
the CPU itself can execute instructions incorrectly, if the supply voltage for executing instructions
is too low.
Flash corruption can easily be avoided by following these design recommendations (one is
sufficient):
1. If there is no need for a Boot Loader update in the system, program the Boot Loader Lock
bits to prevent any Boot Loader software updates.
2. Keep the AVR RESET active (low) during periods of insufficient power supply voltage.
This can be done by enabling the internal Brown-out Detector (BOD) if the operating volt-
age matches the detection level. If not, an external low VCC reset protection circuit can be
Bit 76543210
Rd – – BLB12 BLB11 BLB02 BLB01 LB2 LB1
Bit 76543210
Rd FLB7 FLB6 FLB5 FLB4 FLB3 FLB2 FLB1 FLB0
Bit 76543210
Rd FHB7 FHB6 FHB5 FHB4 FHB3 FHB2 FHB1 FHB0
Bit 76543210
Rd – – – – – EFB2EFB1EFB0
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used. If a reset occurs while a write operation is in progress, the write operation will be
completed provided that the power supply voltage is sufficient.
3. Keep the AVR core in Power-down sleep mode during periods of low VCC. This will pre-
vent the CPU from attempting to decode and execute instructions, effectively protecting
the SPMCSR Register and thus the Flash from unintentional writes.
26.7.11 Programming Time for Flash when Using SPM
The calibrated RC Oscillator is used to time Flash accesses. Table 26-5 shows the typical pro-
gramming time for Flash accesses from the CPU.
Table 26-5. SPM Programming Time
Symbol Min Programming Time Max Programming Time
Flash write (Page Erase, Page Write,
and write Lock bits by SPM) 3.7ms 4.5ms
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26.7.12 Simple Assembly Code Example for a Boot Loader
;-the routine writes one page of data from RAM to Flash
; the first data location in RAM is pointed to by the Y pointer
; the first data location in Flash is pointed to by the Z-pointer
;-error handling is not included
;-the routine must be placed inside the Boot space
; (at least the Do_spm sub routine). Only code inside NRWW section can
; be read during Self-Programming (Page Erase and Page Write).
;-registers used: r0, r1, temp1 (r16), temp2 (r17), looplo (r24),
; loophi (r25), spmcrval (r20)
; storing and restoring of registers is not included in the routine
; register usage can be optimized at the expense of code size
;-It is assumed that either the interrupt table is moved to the Boot
; loader section or that the interrupts are disabled.
.equ PAGESIZEB = PAGESIZE*2 ;PAGESIZEB is page size in BYTES, not words
.org SMALLBOOTSTART
Write_page:
; Page Erase
ldi spmcrval, (1<<PGERS) | (1<<SPMEN)
call Do_spm
; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call Do_spm
; transfer data from RAM to Flash page buffer
ldi looplo, low(PAGESIZEB) ;init loop variable
ldi loophi, high(PAGESIZEB) ;not required for PAGESIZEB<=256
Wrloop:
ld r0, Y+
ld r1, Y+
ldi spmcrval, (1<<SPMEN)
call Do_spm
adiw ZH:ZL, 2
sbiw loophi:looplo, 2 ;use subi for PAGESIZEB<=256
brne Wrloop
; execute Page Write
subi ZL, low(PAGESIZEB) ;restore pointer
sbci ZH, high(PAGESIZEB) ;not required for PAGESIZEB<=256
ldi spmcrval, (1<<PGWRT) | (1<<SPMEN)
call Do_spm
; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call Do_spm
; read back and check, optional
ldi looplo, low(PAGESIZEB) ;init loop variable
ldi loophi, high(PAGESIZEB) ;not required for PAGESIZEB<=256
subi YL, low(PAGESIZEB) ;restore pointer
sbci YH, high(PAGESIZEB)
Rdloop:
lpm r0, Z+
ld r1, Y+
cpse r0, r1
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jmp Error
sbiw loophi:looplo, 1 ;use subi for PAGESIZEB<=256
brne Rdloop
; return to RWW section
; verify that RWW section is safe to read
Return:
in temp1, SPMCSR
sbrs temp1, RWWSB ; If RWWSB is set, the RWW section is not ready yet
ret
; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call Do_spm
rjmp Return
Do_spm:
; check for previous SPM complete
Wait_spm:
in temp1, SPMCSR
sbrc temp1, SPMEN
rjmp Wait_spm
; input: spmcrval determines SPM action
; disable interrupts if enabled, store status
in temp2, SREG
cli
; check that no EEPROM write access is present
Wait_ee:
sbic EECR, EEWE
rjmp Wait_ee
; SPM timed sequence
out SPMCSR, spmcrval
spm
; restore SREG (to enable interrupts if originally enabled)
out SREG, temp2
ret
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26.7.13 ATmega329/3290/649/6490 Boot Loader Parameters
In Table 26-6 through Table 26-8, the parameters used in the description of the Self-Program-
ming are given.
Notes: 1. The different BOOTSZ Fuse configurations are shown in Figure 26-2
Notes: 1. For details about these two section, see “NRWW – No Read-While-Write Section” on page 279 and “RWW – Read-While-
Write Section” on page 279.
Notes: 1. Z0: should be zero for all SPM commands, byte select for the LPM instruction. See “Addressing the Flash During Self-Pro-
gramming” on page 283 for details about the use of Z-pointer during Self-Programming.
Table 26-6. Boot Size Configuration(1)
BOOTSZ1 BOOTSZ0 Boot Size Pages
Application
Flash Section
Boot Loader
Flash Section
End
Application
Section
Boot Reset
Address
(Start
Boot Loader
Section)
1 1 256/512 words 4 0x0000-0x3EFF/
0x0000 -0x7DFF
0x3F00-0x3FFF/
0x7E00-0x7FFF
0x3EFF/
0x7DFF
0x3F00/
0x7E00
1 0 512/1024 words 80x0000-0x3DFF/
0x0000-0x7BFF/
0x3E00-0x3FFF/
0x7C00-0x7FFF
0x3DFF/
0x7BFF
0x3E00/
0x7C00
0 1 1024/2048 words 16 0x0000-0x3BFF/
0x0000-0x77FF
0x3C00-0x3FFF/
0x7800-0x7FFF
0x3BFF/
0x77FF
0x3C00
0x7800
0 0 2048/4096 words 32 0x0000-0x37FF/
0x0000 -0x6FFF
0x3800-0x3FFF/
0x7000-0x7FFF
0x37FF/
0x6FFF
0x3800/
0x7000
Table 26-7. Read-While-Write Limit(1)
Section Pages Address
Read-While-Write section (RWW) 224/224 0x0000 - 0x37FF/ 0x0000 - 0x6FFF
No Read-While-Write section (NRWW) 32/32 0x3800 - 0x3FFF/ 0x7000-0x7FFF
Table 26-8. Explanation of different variables used in Figure 26-3 and the mapping to the Z-pointer(1)
Variable
Corresponding
Z-value Description
PCMSB 13/14 Most significant bit in the Program Counter. (Program Counter is 14/15
bits PC[13/14:0])
PAGEMSB 5/6 Most significant bit which is used to address the words within one page
(64/128 words in a page requires six/seven bits PC [5/6:0]).
ZPCMSB Z14/15 Bit in Z-register that is mapped to PCMSB. Because Z0 is not used, the
ZPCMSB equals PCMSB + 1.
ZPAGEMSB Z6/7 Bit in Z-register that is mapped to PCMSB. Because Z0 is not used, the
ZPAGEMSB equals PAGEMSB + 1.
PCPAGE PC[13/14:6/7] Z14/15:Z7/8Program Counter page address: Page select, for Page Erase and Page
Write
PCWORD PC[5/6:0] Z6/7:Z1 Program Counter word address: Word select, for filling temporary buffer
(must be zero during Page Write operation)
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26.8 Register Description
26.8.1 SPMCSR – Store Program Memory Control and Status Register
The Store Program Memory Control and Status Register contains the control bits needed to con-
trol the Boot Loader operations.
• Bit 7 – SPMIE: SPM Interrupt Enable
When the SPMIE bit is written to one, and the I-bit in the Status Register is set (one), the SPM
ready interrupt will be enabled. The SPM ready Interrupt will be executed as long as the SPMEN
bit in the SPMCSR Register is cleared.
• Bit 6 – RWWSB: Read-While-Write Section Busy
When a Self-Programming (Page Erase or Page Write) operation to the RWW section is initi-
ated, the RWWSB will be set (one) by hardware. When the RWWSB bit is set, the RWW section
cannot be accessed. The RWWSB bit will be cleared if the RWWSRE bit is written to one after a
Self-Programming operation is completed. Alternatively the RWWSB bit will automatically be
cleared if a page load operation is initiated.
• Bit 5 – Reserved Bit
This bit is a reserved bit in the ATmega329/3290/649/6490 and always read as zero.
• Bit 4 – RWWSRE: Read-While-Write Section Read Enable
When programming (Page Erase or Page Write) to the RWW section, the RWW section is
blocked for reading (the RWWSB will be set by hardware). To re-enable the RWW section, the
user software must wait until the programming is completed (SPMEN will be cleared). Then, if
the RWWSRE bit is written to one at the same time as SPMEN, the next SPM instruction within
four clock cycles re-enables the RWW section. The RWW section cannot be re-enabled while
the Flash is busy with a Page Erase or a Page Write (SPMEN is set). If the RWWSRE bit is writ-
ten while the Flash is being loaded, the Flash load operation will abort and the data loaded will
be lost.
• Bit 3 – BLBSET: Boot Lock Bit Set
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock
cycles sets Boot Lock bits and general Lock bits, according to the data in R0. The data in R1 and
the address in the Z-pointer are ignored. The BLBSET bit will automatically be cleared upon
completion of the Lock bit set, or if no SPM instruction is executed within four clock cycles.
An LPM instruction within three cycles after BLBSET and SPMEN are set in the SPMCSR Reg-
ister, will read either the Lock bits or the Fuse bits (depending on Z0 in the Z-pointer) into the
destination register. See “Reading the Fuse and Lock Bits from Software” on page 285 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
Bit 7 6 5 4 3 2 1 0
0x37 (0x57) SPMIE RWWSB – RWWSRE BLBSET PGWRT PGERS SPMEN SPMCSR
Read/Write R/W R R R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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clock cycles. The CPU is halted during the entire Page Write operation if the NRWW section is
addressed.
• Bit 1 – PGERS: Page Erase
If this bit is written to one at the same time as 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 if the NRWW section is addressed.
• 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 RWWSRE, BLBSET, PGWRT’ or PGERS, the following SPM instruction will have a spe-
cial 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.
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27. Memory Programming
27.1 Program And Data Memory Lock Bits
The ATmega329/3290/649/6490 provides six Lock bits which can be left unprogrammed (“1”) or
can be programmed (“0”) to obtain the additional features listed in Table 27-2. The Lock bits can
only be erased to “1” with the Chip Erase command.
Note: 1. “1” means unprogrammed, “0” means programmed
Table 27-1. Lock Bit Byte(1)
Lock Bit Byte Bit No Description Default Value
7 – 1 (unprogrammed)
6 – 1 (unprogrammed)
BLB12 5 Boot Lock bit 1 (unprogrammed)
BLB11 4 Boot Lock bit 1 (unprogrammed)
BLB02 3 Boot Lock bit 1 (unprogrammed)
BLB01 2 Boot Lock bit 1 (unprogrammed)
LB2 1 Lock bit 1 (unprogrammed)
LB1 0 Lock bit 1 (unprogrammed)
Table 27-2. Lock Bit Protection Modes(1)(2)
Memory Lock Bits Protection Type
LB Mode LB2 LB1
111No memory lock features enabled.
210
Further programming of the Flash and EEPROM is
disabled in Parallel and Serial Programming mode. The
Fuse bits are locked in both Serial and Parallel
Programming mode.(1)
300
Further programming and verification of the Flash and
EEPROM is disabled in Parallel and Serial Programming
mode. The Boot Lock bits and Fuse bits are locked in both
Serial and Parallel Programming mode.(1)
BLB0 Mode BLB02 BLB01
111
No restrictions for SPM or LPM accessing the Application
section.
2 1 0 SPM is not allowed to write to the Application section.
300
SPM is not allowed to write to the Application section, and
LPM executing from the Boot Loader section is not
allowed to read from the Application section. If Interrupt
Vectors are placed in the Boot Loader section, interrupts
are disabled while executing from the Application section.
401
LPM executing from the Boot Loader section is not
allowed to read from the Application section. If Interrupt
Vectors are placed in the Boot Loader section, interrupts
are disabled while executing from the Application section.
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Notes: 1. Program the Fuse bits and Boot Lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
27.2 Fuse Bits
The ATmega329/3290/649/6490 has three Fuse bytes. Table 27-3 - Table 27-5 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.
Notes: 1. See Table 28-5 on page 330 for BODLEVEL Fuse decoding.
2. Port G, PG5 is input only. Pull-up is always on. See “Alternate Functions of Port G” on page
79.
BLB1 Mode BLB12 BLB11
111
No restrictions for SPM or LPM accessing the Boot Loader
section.
2 1 0 SPM is not allowed to write to the Boot Loader section.
300
SPM is not allowed to write to the Boot Loader section,
and LPM executing from the Application section is not
allowed to read from the Boot Loader section. If Interrupt
Vectors are placed in the Application section, interrupts
are disabled while executing from the Boot Loader section.
401
LPM executing from the Application section is not allowed
to read from the Boot Loader section. If Interrupt Vectors
are placed in the Application section, interrupts are
disabled while executing from the Boot Loader section.
Table 27-2. Lock Bit Protection Modes(1)(2) (Continued)
Memory Lock Bits Protection Type
Table 27-3. Extended Fuse Byte
Extended Fuse Byte Bit No Description Default Value
–7– 1
–6– 1
–5– 1
–4– 1
–5– 1
BODLEVEL1(1) 2 Brown-out Detector trigger level 1 (unprogrammed)
BODLEVEL0(1) 1 Brown-out Detector trigger level 1 (unprogrammed)
RSTDISBL(2) 0 External Reset Disable 1 (unprogrammed)
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Note: 1. The SPIEN Fuse is not accessible in serial programming mode.
2. The default value of BOOTSZ1..0 results in maximum Boot Size. See Table 26-6 on page 290
for details.
3. See “WDTCR – Watchdog Timer Control Register” on page 48 for details.
4. Never ship a product with the OCDEN Fuse programmed regardless of the setting of Lock bits
and JTAGEN Fuse. A programmed OCDEN Fuse enables some parts of the clock system to
be running in all sleep modes. This may increase the power consumption.
5. If the JTAG interface is left unconnected, the JTAGEN fuse should if possible be disabled. This
to avoid static current at the TDO pin in the JTAG interface.
Note: 1. The default value of SUT1..0 results in maximum start-up time for the default clock source.
See Table 28-4 on page 330 for details.
2. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8MHz. See Table 8-5 on
page 29 for details.
3. The CKOUT Fuse allow the system clock to be output on PORTE7. See “Clock Output Buffer”
on page 31 for details.
4. See “System Clock Prescaler” on page 32 for details.
Table 27-4. Fuse High Byte
Fuse High Byte Bit No Description Default Value
OCDEN(4) 7 Enable OCD
1 (unprogrammed,
OCD disabled)
JTAGEN(5) 6 Enable JTAG
0 (programmed, JTAG
enabled)
SPIEN(1) 5
Enable Serial Program and Data
Downloading
0 (programmed, SPI
prog. enabled)
WDTON(3) 4 Watchdog Timer always on 1 (unprogrammed)
EESAVE 3
EEPROM memory is preserved
through the Chip Erase
1 (unprogrammed,
EEPROM not
preserved)
BOOTSZ1 2
Select Boot Size (see Table 27-6
for details) 0 (programmed)(2)
BOOTSZ0 1
Select Boot Size (see Table 27-6
for details) 0 (programmed)(2)
BOOTRST 0 Select Reset Vector 1 (unprogrammed)
Table 27-5. Fuse Low Byte
Fuse Low Byte Bit No Description Default Value
CKDIV8(4) 7 Divide clock by 80 (programmed)
CKOUT(3) 6 Clock output 1 (unprogrammed)
SUT1 5 Select start-up time 1 (unprogrammed)(1)
SUT0 4 Select start-up time 0 (programmed)(1)
CKSEL3 3 Select Clock source 0 (programmed)(2)
CKSEL2 2 Select Clock source 0 (programmed)(2)
CKSEL1 1 Select Clock source 1 (unprogrammed)(2)
CKSEL0 0 Select Clock source 0 (programmed)(2)
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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.
27.2.1 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.
27.3 Signature Bytes
All Atmel microcontrollers have a three-byte signature code which identifies the device. This
code can be read in both serial and parallel mode, also when the device is locked. The three
bytes reside in a separate address space.
For the ATmega329/3290/649/6490 the signature bytes are:
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x95/0x96 (indicates Flash memory,refer to “Part Number” on page 252).
3. 0x002: 0x03/0x04 (indicates device, refer to “Part Number” on page 252).
27.4 Calibration Byte
The ATmega329/3290/649/6490 has a byte calibration value for the internal RC Oscillator. This
byte resides in the high byte of address 0x000 in the signature address space. During reset, this
byte is automatically written into the OSCCAL Register to ensure correct frequency of the cali-
brated RC Oscillator.
27.5 Parallel Programming Parameters, Pin Mapping, and Commands
This section describes how to parallel program and verify Flash Program memory, EEPROM
Data memory, Memory Lock bits, and Fuse bits in the ATmega329/3290/649/6490. Pulses are
assumed to be at least 250ns unless otherwise noted.
27.5.1 Signal Names
In this section, some pins of the ATmega329/3290/649/6490 are referenced by signal names
describing their functionality during parallel programming, see Figure 27-1 and Table 27-6. Pins
not described in the following table are referenced by pin names.
The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse.
The bit coding is shown in Table 27-8.
When pulsing WR or OE, the command loaded determines the action executed. The different
Commands are shown in Table 27-9.
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Figure 27-1. Parallel Programming
Table 27-6. Pin Name Mapping
Signal Name in
Programming Mode Pin Name I/O Function
RDY/BSY PD1 O 0: Device is busy programming, 1: Device is ready
for new command.
OE PD2 I Output Enable (Active low).
WR PD3 I Write Pulse (Active low).
BS1 PD4 I Byte Select 1 (“0” selects low byte, “1” selects high
byte).
XA0 PD5 I XTAL Action Bit 0
XA1 PD6 I XTAL Action Bit 1
PAGEL PD7 I Program Memory and EEPROM data Page Load.
BS2 PA0 I Byte Select 2 (“0” selects low byte, “1” selects 2’nd
high byte).
DATA PB7-0 I/O Bi-directional Data bus (Output when OE is low).
Table 27-7. Pin Values Used to Enter Programming Mode
Pin Symbol Value
PAGEL Prog_enable[3] 0
XA1 Prog_enable[2] 0
XA0 Prog_enable[1] 0
BS1 Prog_enable[0] 0
VCC
+5V
GND
XTAL1
PD1
PD2
PD3
PD4
PD5
PD6
PB7 - PB0 DATA
RESET
PD7
+12 V
BS1
XA0
XA1
OE
RDY/BSY
PAGEL
PA0
WR
BS2
AVCC
+5V
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Table 27-8. XA1 and XA0 Coding
XA1 XA0 Action when XTAL1 is Pulsed
0 0 Load Flash or EEPROM Address (High or low address byte
determined by BS1).
0 1 Load Data (High or Low data byte for Flash determined by BS1).
1 0 Load Command
11No Action, Idle
Table 27-9. Command Byte Bit Coding
Command Byte Command Executed
1000 0000 Chip Erase
0100 0000 Write Fuse bits
0010 0000 Write Lock bits
0001 0000 Write Flash
0001 0001 Write EEPROM
0000 1000 Read Signature Bytes and Calibration byte
0000 0100 Read Fuse and Lock bits
0000 0010 Read Flash
0000 0011 Read EEPROM
Table 27-10. No. of Words in a Page and No. of Pages in the Flash
Flash Size Page Size PCWORD No. of Pages PCPAGE PCMSB
16/32K words
(32/64K bytes)
64/128
words PC[5/6:0] 256 PC
[13/14:6/7] 13/14
Table 27-11. No. of Words in a Page and No. of Pages in the EEPROM
EEPROM Size Page Size PCWORD No. of Pages PCPAGE EEAMSB
1K/2K bytes 4/8 bytes EEA[1/2:0] 256 EEA
[13/14:2/3] 13/14
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27.6 Parallel Programming
27.6.1 Enter Programming Mode
The following algorithm puts the device in Parallel (High-voltage) Programming mode:
1. Set Prog_enable pins listed in Table 27-7 on page 297 to “0000”, RESET pin and VCC to
0V.
2. Apply 4.5 - 5.5V between VCC and GND.
3. Ensure that VCC reaches at least 1.8V within the next 20 µs.
4. Wait 20 - 60 µs, and apply 11.5 - 12.5V to RESET.
5. Keep the Prog_enable pins unchanged for at least 10µs after the High-voltage has been
applied to ensure the Prog_enable Signature has been latched.
6. Wait at least 300 µs before giving any parallel programming commands.
7. Exit Programming mode by power the device down or by bringing RESET pin to 0V.
If the rise time of the VCC is unable to fulfill the requirements listed above, the following alterna-
tive algorithm can be used.
1. Set Prog_enable pins listed in Table 27-7 on page 297 to “0000”, RESET pin to 0V and
VCC to 0V.
2. Apply 4.5 - 5.5V between VCC and GND.
3. Monitor VCC, and as soon as VCC reaches 0.9 - 1.1V, apply 11.5 - 12.5V to RESET.
4. Keep the Prog_enable pins unchanged for at least 10µs after the High-voltage has been
applied to ensure the Prog_enable Signature has been latched.
5. Wait until VCC actually reaches 4.5 -5.5V before giving any parallel programming
commands.
6. Exit Programming mode by power the device down or by bringing RESET pin to 0V.
27.6.2 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.
27.6.3 Chip Erase
The Chip Erase will erase the Flash and EEPROM(1) memories plus Lock bits. The Lock bits are
not reset until the program memory has been completely erased. The Fuse bits are not
changed. A Chip Erase must be performed before the Flash and/or EEPROM are
reprogrammed.
Note: 1. The EEPRPOM memory is preserved during Chip Erase if the EESAVE Fuse is programmed.
Load Command “Chip Erase”
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1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “1000 0000”. This is the command for Chip Erase.
4. Give XTAL1 a positive pulse. This loads the command.
5. Give WR a negative pulse. This starts the Chip Erase. RDY/BSY goes low.
6. Wait until RDY/BSY goes high before loading a new command.
27.6.4 Programming the Flash
The Flash is organized in pages, see Table 27-10 on page 298. When programming the Flash,
the program data is latched into a page buffer. This allows one page of program data to be pro-
grammed simultaneously. The following procedure describes how to program the entire Flash
memory:
A. Load Command “Write Flash”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “0001 0000”. This is the command for Write Flash.
4. Give XTAL1 a positive pulse. This loads the command.
B. Load Address Low byte
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “0”. This selects low address.
3. Set DATA = Address low byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address low byte.
C. Load Data Low Byte
1. Set XA1, XA0 to “01”. This enables data loading.
2. Set DATA = Data low byte (0x00 - 0xFF).
3. Give XTAL1 a positive pulse. This loads the data byte.
D. Load Data High Byte
1. Set BS1 to “1”. This selects high data byte.
2. Set XA1, XA0 to “01”. This enables data loading.
3. Set DATA = Data high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the data byte.
E. Latch Data
1. Set BS1 to “1”. This selects high data byte.
2. Give PAGEL a positive pulse. This latches the data bytes. (See Figure 27-3 for signal
waveforms)
F. Repeat B through E until the entire buffer is filled or until all data within the page is loaded.
While the lower bits in the address are mapped to words within the page, the higher bits address
the pages within the FLASH. This is illustrated in Figure 27-2 on page 301. Note that if less than
eight bits are required to address words in the page (pagesize < 256), the most significant bit(s)
in the address low byte are used to address the page when performing a Page Write.
G. Load Address High byte
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1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “1”. This selects high address.
3. Set DATA = Address high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address high byte.
H. Program Page
1. Give WR a negative pulse. This starts programming of the entire page of data. RDY/BSY
goes low.
2. Wait until RDY/BSY goes high (See Figure 27-3 for signal waveforms).
I. Repeat B through H until the entire Flash is programmed or until all data has been
programmed.
J. End Page Programming
1. 1. Set XA1, XA0 to “10”. This enables command loading.
2. Set DATA to “0000 0000”. This is the command for No Operation.
3. Give XTAL1 a positive pulse. This loads the command, and the internal write signals are
reset.
Figure 27-2. Addressing the Flash Which is Organized in Pages(1)
Note: 1. PCPAGE and PCWORD are listed in Table 27-10 on page 298.
PROGRAM MEMORY
WORD ADDRESS
WITHIN A PAGE
PAGE ADDRESS
WITHIN THE FLASH
INSTRUCTION WORD
PA G E PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
PA G E
PCWORDPCPAGE
PCMSB PAGEMSB
PROGRAM
COUNTER
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Figure 27-3. Programming the Flash Waveforms(1)
Note: 1. “XX” is don’t care. The letters refer to the programming description above.
27.6.5 Programming the EEPROM
The EEPROM is organized in pages, see Table 27-11 on page 298. When programming the
EEPROM, the program data is latched into a page buffer. This allows one page of data to be
programmed simultaneously. The programming algorithm for the EEPROM data memory is as
follows (refer to “Programming the Flash” on page 300 for details on Command, Address and
Data loading):
1. A: Load Command “0001 0001”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. C: Load Data (0x00 - 0xFF).
5. E: Latch data (give PAGEL a positive pulse).
K: Repeat 3 through 5 until the entire buffer is filled.
L: Program EEPROM page
1. Set BS1 to “0”.
2. Give WR a negative pulse. This starts programming of the EEPROM page. RDY/BSY
goes low.
3. Wait until to RDY/BSY goes high before programming the next page (See Figure 27-4 for
signal waveforms).
RDY/BSY
WR
OE
RESET +12V
PAGEL
BS2
0x10 ADDR. LOW ADDR. HIGH
DATA DATA LOW DATA HIGH ADDR. LOW DATA LOW DATA HIGH
XA1
XA0
BS1
XTAL1
XX XX XX
ABCDEBCDEGH
F
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Figure 27-4. Programming the EEPROM Waveforms
27.6.6 Reading the Flash
The algorithm for reading the Flash memory is as follows (refer to “Programming the Flash” on
page 300 for details on Command and Address loading):
1. A: Load Command “0000 0010”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The Flash word low byte can now be read at DATA.
5. Set BS1 to “1”. The Flash word high byte can now be read at DATA.
6. Set OE to “1”.
27.6.7 Reading the EEPROM
The algorithm for reading the EEPROM memory is as follows (refer to “Programming the Flash”
on page 300 for details on Command and Address loading):
1. A: Load Command “0000 0011”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The EEPROM Data byte can now be read at DATA.
5. Set OE to “1”.
27.6.8 Programming the Fuse Low Bits
The algorithm for programming the Fuse Low bits is as follows (refer to “Programming the Flash”
on page 300 for details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
27.6.9 Programming the Fuse High Bits
The algorithm for programming the Fuse High bits is as follows (refer to “Programming the
Flash” on page 300 for details on Command and Data loading):
RDY/BSY
WR
OE
RESET +12V
PAGEL
BS2
0x11 ADDR. HIGH
DATA ADDR. LOW DATA ADDR. LOW DATA XX
XA1
XA0
BS1
XTAL1
XX
AGBCEB C EL
K
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1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Set BS1 to “1” and BS2 to “0”. This selects high data byte.
4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. Set BS1 to “0”. This selects low data byte.
27.6.10 Programming the Extended Fuse Bits
The algorithm for programming the Extended Fuse bits is as follows (refer to “Programming the
Flash” on page 300 for details on Command and Data loading):
1. 1. A: Load Command “0100 0000”.
2. 2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. 3. Set BS1 to “0” and BS2 to “1”. This selects extended data byte.
4. 4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. 5. Set BS2 to “0”. This selects low data byte.
Figure 27-5. Programming the FUSES Waveforms
27.6.11 Programming the Lock Bits
The algorithm for programming the Lock bits is as follows (refer to “Programming the Flash” on
page 300 for details on Command and Data loading):
1. A: Load Command “0010 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs the Lock bit. If LB mode 3 is programmed
(LB1 and LB2 is programmed), it is not possible to program the Boot Lock bits by any
External Programming mode.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
The Lock bits can only be cleared by executing Chip Erase.
27.6.12 Reading the Fuse and Lock Bits
The algorithm for reading the Fuse and Lock bits is as follows (refer to “Programming the Flash”
on page 300 for details on Command loading):
RDY/BSY
WR
OE
RESET +12V
PAGEL
0x40
DATA
DATA XX
XA1
XA0
BS1
XTAL1
AC
0x40 DATA XX
AC
Write Fuse Low byte Write Fuse high byte
0x40 DATA XX
AC
Write Extended Fuse byte
BS2
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1. A: Load Command “0000 0100”.
2. Set OE to “0”, BS2 to “0” and BS1 to “0”. The status of the Fuse Low bits can now be
read at DATA (“0” means programmed).
3. Set OE to “0”, BS2 to “1” and BS1 to “1”. The status of the Fuse High bits can now be
read at DATA (“0” means programmed).
4. Set OE to “0”, BS2 to “1”, and BS1 to “0”. The status of the Extended Fuse bits can now
be read at DATA (“0” means programmed).
5. Set OE to “0”, BS2 to “0” and BS1 to “1”. The status of the Lock bits can now be read at
DATA (“0” means programmed).
6. Set OE to “1”.
Figure 27-6. Mapping Between BS1, BS2 and the Fuse and Lock Bits During Read
27.6.13 Reading the Signature Bytes
The algorithm for reading the Signature bytes is as follows (refer to “Programming the Flash” on
page 300 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte (0x00 - 0x02).
3. Set OE to “0”, and BS1 to “0”. The selected Signature byte can now be read at DATA.
4. Set OE to “1”.
27.6.14 Reading the Calibration Byte
The algorithm for reading the Calibration byte is as follows (refer to “Programming the Flash” on
page 300 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte, 0x00.
3. Set OE to “0”, and BS1 to “1”. The Calibration byte can now be read at DATA.
4. Set OE to “1”.
Lock Bits 0
1
BS2
Fuse High Byte
0
1
BS1
DATA
Fuse Low Byte 0
1
BS2
Extended Fuse Byte
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27.6.15 Parallel Programming Characteristics
Figure 27-7. Parallel Programming Timing, Including some General Timing Requirements
Figure 27-8. Parallel Programming Timing, Loading Sequence with Timing Requirements(1)
Note: 1. The timing requirements shown in Figure 27-7 (i.e., tDVXH, tXHXL, and tXLDX) also apply to load-
ing operation.
Data & Contol
(DATA, XA0/1, BS1, BS2)
XTAL1
t
XHXL
t
WLWH
t
DVXH
t
XLDX
t
PLWL
t
WLRH
WR
RDY/BSY
PAGEL
t
PHPL
t
PLBX
t
BVPH
t
XLWL
t
WLBX
t
BVWL
WLRL
XTAL1
PAGEL
t
PLXH
XLXH
tt
XLPH
ADDR0 (Low Byte) DATA (Low Byte) DATA (High Byte) ADDR1 (Low Byte)
DATA
BS1
XA0
XA1
LOAD ADDRESS
(LOW BYTE)
LOAD DATA
(LOW BYTE)
LOAD DATA
(HIGH BYTE)
LOAD DATA
LOAD ADDRESS
(LOW BYTE)
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Figure 27-9. Parallel Programming Timing, Reading Sequence (within the Same Page) with
Timing Requirements(1)
Note: 1. The timing requirements shown in Figure 27-7 (i.e., tDVXH, tXHXL, and tXLDX) also apply to read-
ing operation.
Table 27-12. Parallel Programming Characteristics, VCC = 5V ± 10%
Symbol Parameter Min Typ Max Units
VPP Programming Enable Voltage 11.5 12.5 V
IPP Programming Enable Current 250 μA
tDVXH Data and Control Valid before XTAL1 High 67 ns
tXLXH XTAL1 Low to XTAL1 High 200 ns
tXHXL XTAL1 Pulse Width High 150 ns
tXLDX Data and Control Hold after XTAL1 Low 67 ns
tXLWL XTAL1 Low to WR Low 0 ns
tXLPH XTAL1 Low to PAGEL high 0 ns
tPLXH PAGEL low to XTAL1 high 150 ns
tBVPH BS1 Valid before PAGEL High 67 ns
tPHPL PAGEL Pulse Width High 150 ns
tPLBX BS1 Hold after PAGEL Low 67 ns
tWLBX BS2/1 Hold after WR Low 67 ns
tPLWL PAGEL Low to WR Low 67 ns
tBVWL BS1 Valid to WR Low 67 ns
tWLWH WR Pulse Width Low 150 ns
tWLRL WR Low to RDY/BSY Low 0 1 μs
tWLRH WR Low to RDY/BSY High(1) 3.7 4.5 ms
tWLRH_CE WR Low to RDY/BSY High for Chip Erase(2) 7.5 9 ms
tXLOL XTAL1 Low to OE Low 0 ns
XTAL1
OE
ADDR0 (Low Byte) DATA (Low Byte) DATA (High Byte) ADDR1 (Low Byte)
DATA
BS1
XA0
XA1
LOAD ADDRESS
(LOW BYTE)
READ DATA
(LOW BYTE)
READ DATA
(HIGH BYTE)
LOAD ADDRESS
(LOW BYTE)
t
BVDV
t
OLDV
t
XLOL
t
OHDZ
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Notes: 1. tWLRH is valid for the Write Flash, Write EEPROM, Write Fuse bits and Write Lock bits
commands.
2. tWLRH_CE is valid for the Chip Erase command.
27.7 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 (out-
put). After RESET is set low, the Programming Enable instruction needs to be executed first
before program/erase operations can be executed. NOTE, in Table 27-13 on page 308, the pin
mapping for SPI programming is listed. Not all parts use the SPI pins dedicated for the internal
SPI interface.
27.7.1 Serial Programming Pin Mapping
Figure 27-10. Serial Programming and Verify(1)
Notes: 1. If the device is clocked by the internal Oscillator, it is no need to connect a clock source to the
XTAL1 pin.
2. VCC - 0.3V < AVCC < VCC + 0.3V, however, AVCC should always be within 1.8 - 5.5V
When programming the EEPROM, an auto-erase cycle is built into the self-timed programming
operation (in the Serial mode ONLY) and there is no need to first execute the Chip Erase
instruction. The Chip Erase operation turns the content of every memory location in both the
Program and EEPROM arrays into 0xFF.
Depending on CKSEL Fuses, a valid clock must be present. The minimum low and high periods
for the serial clock (SCK) input are defined as follows:
tBVDV BS1 Valid to DATA valid 0 250 ns
tOLDV OE Low to DATA Valid 250 ns
tOHDZ OE High to DATA Tri-stated 250 ns
Table 27-12. Parallel Programming Characteristics, VCC = 5V ± 10% (Continued)
Symbol Parameter Min Typ Max Units
Table 27-13. Pin Mapping Serial Programming
Symbol Pins I/O Description
MOSI PB2 I Serial Data in
MISO PB3 O Serial Data out
SCK PB1 I Serial Clock
VCC
GND
XTAL1
SCK
MISO
MOSI
RESET
+1.8 - 5.5V
AVCC
+1.8 - 5.5V
(2)
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Low: > 2 CPU clock cycles for fck < 12MHz, 3 CPU clock cycles for fck ≥ 12MHz
High: > 2 CPU clock cycles for fck < 12MHz, 3 CPU clock cycles for fck ≥ 12MHz
27.7.2 Serial Programming Algorithm
When writing serial data to the ATmega329/3290/649/6490, data is clocked on the rising edge of
SCK.
When reading data from the ATmega329/3290/649/6490, data is clocked on the falling edge of
SCK. See Figure 27-11 for timing details.
To program and verify the ATmega329/3290/649/6490 in the serial programming mode, the fol-
lowing sequence is recommended (See four byte instruction formats in Table 27-15):
1. Power-up sequence:
Apply power between VCC and GND while RESET and SCK are set to “0”. In some sys-
tems, the programmer can not guarantee that SCK is held low during power-up. In this
case, RESET must be given a positive pulse of at least two CPU clock cycles duration
after SCK has been set to “0”.
2. Wait for at least 20ms and enable serial programming by sending the Programming
Enable serial instruction to pin MOSI.
3. The serial programming instructions will not work if the communication is out of synchro-
nization. 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 page size is found in Table 27-10 on
page 298. The memory page is loaded one byte at a time by supplying the 6/7 LSB of the
address and data together with the Load Program Memory Page instruction. To ensure
correct loading of the page, the data low byte must be loaded before data high byte is
applied for a given address. The Program Memory Page is stored by loading the Write
Program Memory Page instruction with the 8 MSB of the address. If polling is not used,
the user must wait at least tWD_FLASH before issuing the next page. (See Table 27-14.)
Accessing the serial programming interface before the Flash write operation completes
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 27-14.) 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 supplying the 2 LSB 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 4 MSB 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
27-11). 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 con-
tent 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.
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8. Power-off sequence (if needed):
Set RESET to “1”.
Tur n V CC power off.
Figure 27-11. Serial Programming Waveforms
27.7.3 Serial Programming Instruction set
Table 27-15 and Figure 27-12 on page 312 describes the Instruction set.
Table 27-14. Minimum Wait Delay Before Writing the Next Flash or EEPROM Location
Symbol Minimum Wait Delay
tWD_FUSE 4.5ms
tWD_FLASH 4.5ms
tWD_EEPROM 9.0ms
tWD_ERASE 9.0ms
MSB
MSB
LSB
LSB
SERIAL CLOCK INPUT
(SCK)
SERIAL DATA INPUT
(MOSI)
(MISO)
SAMPLE
SERIAL DATA OUTPUT
Table 27-15. Serial Programming Instruction Set
Instruction/Operation
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(1) $4D $00 Extended adr $00
Load Program Memory Page, High byte $48$00 adr LSB high data byte in
Load Program Memory Page, Low byte $40 $00 adr LSB low data byte in
Load EEPROM Memory Page (page access) $C1 $00 0000 00aa
/
0000 0aaa
data byte in
Read Instructions
Read Program Memory, High byte $28adr 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 0000 00aa
/
0000 0aaa
aaaa aaaa data byte out
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Note: 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 correspondig section for Fuse and Lock bits, Calibration and Signature bytes and Page size.
6. See htt://www.atmel.com/avr for Application Notes regarding programming and programmers.
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 27-12.
Read Lock bits $58$00 $00 data byte out
Read Signature Byte $30 $00 0000 000aa 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
Write Program Memory Page $4C adr MSB adr LSB $00
Write EEPROM Memory $C0 0000 00aa
/
0000 0aaa
aaaa aaaa data byte in
Write EEPROM Memory Page (page access) $C2 0000 00aa
/
0000 0aaa
aaaa aa00
/
aaaa a000
$00
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 27-15. Serial Programming Instruction Set
Instruction/Operation
Instruction Format
Byte 1 Byte 2 Byte 3 Byte4
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Figure 27-12. Serial Programming Instruction example
27.7.4 SPI Serial Programming Characteristics
For characteristics of the SPI module see “SPI Timing Characteristics” on page 331.
Byte 1 Byte 2 Byte 3 Byte 4
Adr LSB
Bit 15 B 0
Serial Programming Instruction
Program Memory/
EEPROM Memory
Page 0
Page 1
Page 2
Page N-1
Page Buffer
Write Program Memory Page/
Write EEPROM Memory Page
Load Program Memory Page (High/Low Byte)/
Load EEPROM Memory Page (page access)
Byte 1 Byte 2 Byte 3 Byte 4
Bit 15 B 0
Adr MSB
Page Offset
Page Number
Ad
r M
MS
SB
A
A
Adr
r L
LSB
B
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27.8 Programming via the JTAG Interface
Programming through the JTAG interface requires control of the four JTAG specific pins: TCK,
TMS, TDI, and TDO. Control of the reset and clock pins is not required.
To be able to use the JTAG interface, the JTAGEN Fuse must be programmed. The device is
default shipped with the fuse programmed. In addition, the JTD bit in MCUCSR must be cleared.
Alternatively, if the JTD bit is set, the external reset can be forced low. Then, the JTD bit will be
cleared after two chip clocks, and the JTAG pins are available for programming. This provides a
means of using the JTAG pins as normal port pins in Running mode while still allowing In-Sys-
tem Programming via the JTAG interface. Note that this technique can not be used when using
the JTAG pins for Boundary-scan or On-chip Debug. In these cases the JTAG pins must be ded-
icated for this purpose.
During programming the clock frequency of the TCK Input must be less than the maximum fre-
quency of the chip. The System Clock Prescaler can not be used to divide the TCK Clock Input
into a sufficiently low frequency.
As a definition in this data sheet, the LSB is shifted in and out first of all Shift Registers.
27.8.1 Programming Specific JTAG Instructions
The Instruction Register is 4-bit wide, supporting up to 16 instructions. The JTAG instructions
useful for programming are listed below.
The OPCODE for each instruction is shown behind the instruction name in hex format. The text
describes which Data Register is selected as path between TDI and TDO for each instruction.
The Run-Test/Idle state of the TAP controller is used to generate internal clocks. It can also be
used as an idle state between JTAG sequences. The state machine sequence for changing the
instruction word is shown in Figure 27-13.
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Figure 27-13. State Machine Sequence for Changing the Instruction Word
27.8.2 AVR_RESET (0xC)
The AVR specific public JTAG instruction for setting the AVR device in the Reset mode or taking
the device out from the Reset mode. The TAP controller is not reset by this instruction. The one
bit Reset Register is selected as Data Register. Note that the reset will be active as long as there
is a logic “one” in the Reset Chain. The output from this chain is not latched.
The active states are:
• Shift-DR: The Reset Register is shifted by the TCK input.
27.8.3 PROG_ENABLE (0x4)
The AVR specific public JTAG instruction for enabling programming via the JTAG port. The 16-
bit Programming Enable Register is selected as Data Register. The active states are the
following:
• Shift-DR: The programming enable signature is shifted into the Data Register.
• Update-DR: The programming enable signature is compared to the correct value, and
Programming mode is entered if the signature is valid.
Test-Logic-Reset
Run-Test/Idle
Shift-DR
Exit1-DR
Pause-DR
Exit2-DR
Update-DR
Select-IR Scan
Capture-IR
Shift-IR
Exit1-IR
Pause-IR
Exit2-IR
Update-IR
Select-DR Scan
Capture-DR
0
1
011 1
00
00
11
10
1
1
0
1
0
0
10
1
1
0
1
0
0
00
11
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27.8.4 PROG_COMMANDS (0x5)
The AVR specific public JTAG instruction for entering programming commands via the JTAG
port. The 15-bit Programming Command Register is selected as Data Register. The active
states are the following:
• Capture-DR: The result of the previous command is loaded into the Data Register.
• Shift-DR: The Data Register is shifted by the TCK input, shifting out the result of the
previous command and shifting in the new command.
• Update-DR: The programming command is applied to the Flash inputs
• Run-Test/Idle: One clock cycle is generated, executing the applied command (not always
required, see Table 27-16 below).
27.8.5 PROG_PAGELOAD (0x6)
The AVR specific public JTAG instruction to directly load the Flash data page via the JTAG port.
An 8-bit Flash Data Byte Register is selected as the Data Register. This is physically the 8 LSBs
of the Programming Command Register. The active states are the following:
• Shift-DR: The Flash Data Byte Register is shifted by the TCK input.
• Update-DR: The content of the Flash Data Byte Register is copied into a temporary register.
A write sequence is initiated that within 11 TCK cycles loads the content of the temporary
register into the Flash page buffer. The AVR automatically alternates between writing the low
and the high byte for each new Update-DR state, starting with the low byte for the first
Update-DR encountered after entering the PROG_PAGELOAD command. The Program
Counter is pre-incremented before writing the low byte, except for the first written byte. This
ensures that the first data is written to the address set up by PROG_COMMANDS, and
loading the last location in the page buffer does not make the program counter increment
into the next page.
27.8.6 PROG_PAGEREAD (0x7)
The AVR specific public JTAG instruction to directly capture the Flash content via the JTAG port.
An 8-bit Flash Data Byte Register is selected as the Data Register. This is physically the 8 LSBs
of the Programming Command Register. The active states are the following:
• Capture-DR: The content of the selected Flash byte is captured into the Flash Data Byte
Register. The AVR automatically alternates between reading the low and the high byte for
each new Capture-DR state, starting with the low byte for the first Capture-DR encountered
after entering the PROG_PAGEREAD command. The Program Counter is post-incremented
after reading each high byte, including the first read byte. This ensures that the first data is
captured from the first address set up by PROG_COMMANDS, and reading the last location
in the page makes the program counter increment into the next page.
• Shift-DR: The Flash Data Byte Register is shifted by the TCK input.
27.8.7 Data Registers
The Data Registers are selected by the JTAG instruction registers described in section “Pro-
gramming Specific JTAG Instructions” on page 313. The Data Registers relevant for
programming operations are:
• Reset Register
• Programming Enable Register
• Programming Command Register
• Flash Data Byte Register
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27.8.8 Reset Register
The Reset Register is a Test Data Register used to reset the part during programming. It is
required to reset the part before entering Programming mode.
A high value in the Reset Register corresponds to pulling the external reset low. The part is reset
as long as there is a high value present in the Reset Register. Depending on the Fuse settings
for the clock options, the part will remain reset for a Reset Time-out period (refer to “Clock
Sources” on page 27) after releasing the Reset Register. The output from this Data Register is
not latched, so the reset will take place immediately, as shown in Figure 25-2 on page 253.
27.8.9 Programming Enable Register
The Programming Enable Register is a 16-bit register. The contents of this register is compared
to the programming enable signature, binary code 0b1010_0011_0111_0000. When the con-
tents of the register is equal to the programming enable signature, programming via the JTAG
port is enabled. The register is reset to 0 on Power-on Reset, and should always be reset when
leaving Programming mode.
Figure 27-14. Programming Enable Register
27.8.10 Programming Command Register
The Programming Command Register is a 15-bit register. This register is used to serially shift in
programming commands, and to serially shift out the result of the previous command, if any. The
JTAG Programming Instruction Set is shown in Table 27-16. The state sequence when shifting
in the programming commands is illustrated in Figure 27-16.
TDI
TDO
D
A
T
A
=DQ
ClockDR & PROG_ENABLE
Programming Enable
0xA370
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Figure 27-15. Programming Command Register
TDI
TDO
S
T
R
O
B
E
S
A
D
D
R
E
S
S
/
D
A
T
A
Flash
EEPROM
Fuses
Lock Bits
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Table 27-16. JTAG Programming Instruction Set
a = address high bits, b = address low bits, H = 0 - Low byte, 1 - High Byte, o = data out, i = data in, x = don’t care
Instruction TDI Sequence TDO Sequence Notes
1a. Chip Erase 0100011_10000000
0110001_10000000
0110011_10000000
0110011_10000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
1b. Poll for Chip Erase Complete 0110011_10000000 xxxxxox_xxxxxxxx (2)
2a. Enter Flash Write 0100011_00010000 xxxxxxx_xxxxxxxx
2b. Load Address High Byte 0000111_aaaaaaaa xxxxxxx_xxxxxxxx (9)
2c. Load Address Low Byte 0000011_bbbbbbbb xxxxxxx_xxxxxxxx
2d. Load Data Low Byte 0010011_iiiiiiii xxxxxxx_xxxxxxxx
2e. Load Data High Byte 0010111_iiiiiiii xxxxxxx_xxxxxxxx
2f. Latch Data 0110111_00000000
1110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
2g. Write Flash Page 0110111_00000000
0110101_00000000
0110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
2h. Poll for Page Write Complete 0110111_00000000 xxxxxox_xxxxxxxx (2)
3a. Enter Flash Read 0100011_00000010 xxxxxxx_xxxxxxxx
3b. Load Address High Byte 0000111_aaaaaaaa xxxxxxx_xxxxxxxx (9)
3c. Load Address Low Byte 0000011_bbbbbbbb xxxxxxx_xxxxxxxx
3d. Read Data Low and High Byte 0110010_00000000
0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
xxxxxxx_oooooooo
Low byte
High byte
4a. Enter EEPROM Write 0100011_00010001 xxxxxxx_xxxxxxxx
4b. Load Address High Byte 0000111_aaaaaaaa xxxxxxx_xxxxxxxx (9)
4c. Load Address Low Byte 0000011_bbbbbbbb xxxxxxx_xxxxxxxx
4d. Load Data Byte 0010011_iiiiiiii xxxxxxx_xxxxxxxx
4e. Latch Data 0110111_00000000
1110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
4f. Write EEPROM Page 0110011_00000000
0110001_00000000
0110011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
4g. Poll for Page Write Complete 0110011_00000000 xxxxxox_xxxxxxxx (2)
5a. Enter EEPROM Read 0100011_00000011 xxxxxxx_xxxxxxxx
5b. Load Address High Byte 0000111_aaaaaaaa xxxxxxx_xxxxxxxx (9)
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5c. Load Address Low Byte 0000011_bbbbbbbb xxxxxxx_xxxxxxxx
5d. Read Data Byte 0110011_bbbbbbbb
0110010_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
6a. Enter Fuse Write 0100011_01000000 xxxxxxx_xxxxxxxx
6b. Load Data Low Byte(6) 0010011_iiiiiiii xxxxxxx_xxxxxxxx (3)
6c. Write Fuse Extended Byte 0111011_00000000
0111001_00000000
0111011_00000000
0111011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
6d. Poll for Fuse Write Complete 0110111_00000000 xxxxxox_xxxxxxxx (2)
6e. Load Data Low Byte(7) 0010011_iiiiiiii xxxxxxx_xxxxxxxx (3)
6f. Write Fuse High Byte 0110111_00000000
0110101_00000000
0110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
6g. Poll for Fuse Write Complete 0110111_00000000 xxxxxox_xxxxxxxx (2)
6h. Load Data Low Byte(7) 0010011_iiiiiiii xxxxxxx_xxxxxxxx (3)
6i. Write Fuse Low Byte 0110011_00000000
0110001_00000000
0110011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
6j. Poll for Fuse Write Complete 0110011_00000000 xxxxxox_xxxxxxxx (2)
7a. Enter Lock Bit Write 0100011_00100000 xxxxxxx_xxxxxxxx
7b. Load Data Byte(9) 0010011_11iiiiii xxxxxxx_xxxxxxxx (4)
7c. Write Lock Bits 0110011_00000000
0110001_00000000
0110011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
7d. Poll for Lock Bit Write complete 0110011_00000000 xxxxxox_xxxxxxxx (2)
8a. Enter Fuse/Lock Bit Read 0100011_00000100 xxxxxxx_xxxxxxxx
8b. Read Extended Fuse Byte(6) 0111010_00000000
0111011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
8c. Read Fuse High Byte(7) 0111110_00000000
0111111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
8d. Read Fuse Low Byte(8)0110010_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
8e. Read Lock Bits(9) 0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxoooooo
(5)
Table 27-16. JTAG Programming Instruction Set (Continued)
a = address high bits, b = address low bits, H = 0 - Low byte, 1 - High Byte, o = data out, i = data in, x = don’t care
Instruction TDI Sequence TDO Sequence Notes
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Notes: 1. This command sequence is not required if the seven MSB are correctly set by the previous command sequence (which is
normally the case).
2. Repeat until o = “1”.
3. Set bits to “0” to program the corresponding Fuse, “1” to unprogram the Fuse.
4. Set bits to “0” to program the corresponding Lock bit, “1” to leave the Lock bit unchanged.
5. “0” = programmed, “1” = unprogrammed.
6. The bit mapping for Fuses Extended byte is listed in Table 27-3 on page 294
7. The bit mapping for Fuses High byte is listed in Table 27-4 on page 295
8. The bit mapping for Fuses Low byte is listed in Table 27-5 on page 295
9. The bit mapping for Lock bits byte is listed in Table 27-1 on page 293
10. Address bits exceeding PCMSB and EEAMSB (Table 27-10 and Table 27-11) are don’t care
11. All TDI and TDO sequences are represented by binary digits (0b...).
8f. Read Fuses and Lock Bits 0111010_00000000
0111110_00000000
0110010_00000000
0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
xxxxxxx_oooooooo
xxxxxxx_oooooooo
xxxxxxx_oooooooo
(5)
Fuse Ext. byte
Fuse High byte
Fuse Low byte
Lock bits
9a. Enter Signature Byte Read 0100011_00001000 xxxxxxx_xxxxxxxx
9b. Load Address Byte 0000011_bbbbbbbb xxxxxxx_xxxxxxxx
9c. Read Signature Byte 0110010_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
10a. Enter Calibration Byte Read 0100011_00001000 xxxxxxx_xxxxxxxx
10b. Load Address Byte 0000011_bbbbbbbb xxxxxxx_xxxxxxxx
10c. Read Calibration Byte 0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
11a. Load No Operation Command 0100011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
Table 27-16. JTAG Programming Instruction Set (Continued)
a = address high bits, b = address low bits, H = 0 - Low byte, 1 - High Byte, o = data out, i = data in, x = don’t care
Instruction TDI Sequence TDO Sequence Notes
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Figure 27-16. State Machine Sequence for Changing/Reading the Data Word
27.8.11 Flash Data Byte Register
The Flash Data Byte Register provides an efficient way to load the entire Flash page buffer
before executing Page Write, or to read out/verify the content of the Flash. A state machine sets
up the control signals to the Flash and senses the strobe signals from the Flash, thus only the
data words need to be shifted in/out.
The Flash Data Byte Register actually consists of the 8-bit scan chain and a 8-bit temporary reg-
ister. During page load, the Update-DR state copies the content of the scan chain over to the
temporary register and initiates a write sequence that within 11 TCK cycles loads the content of
the temporary register into the Flash page buffer. The AVR automatically alternates between
writing the low and the high byte for each new Update-DR state, starting with the low byte for the
first Update-DR encountered after entering the PROG_PAGELOAD command. The Program
Counter is pre-incremented before writing the low byte, except for the first written byte. This
ensures that the first data is written to the address set up by PROG_COMMANDS, and loading
the last location in the page buffer does not make the Program Counter increment into the next
page.
During Page Read, the content of the selected Flash byte is captured into the Flash Data Byte
Register during the Capture-DR state. The AVR automatically alternates between reading the
low and the high byte for each new Capture-DR state, starting with the low byte for the first Cap-
Test-Logic-Reset
Run-Test/Idle
Shift-DR
Exit1-DR
Pause-DR
Exit2-DR
Update-DR
Select-IR Scan
Capture-IR
Shift-IR
Exit1-IR
Pause-IR
Exit2-IR
Update-IR
Select-DR Scan
Capture-DR
0
1
011 1
00
00
11
10
1
1
0
1
0
0
10
1
1
0
1
0
0
00
11
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ture-DR encountered after entering the PROG_PAGEREAD command. The Program Counter is
post-incremented after reading each high byte, including the first read byte. This ensures that
the first data is captured from the first address set up by PROG_COMMANDS, and reading the
last location in the page makes the program counter increment into the next page.
Figure 27-17. Flash Data Byte Register
The state machine controlling the Flash Data Byte Register is clocked by TCK. During normal
operation in which eight bits are shifted for each Flash byte, the clock cycles needed to navigate
through the TAP controller automatically feeds the state machine for the Flash Data Byte Regis-
ter with sufficient number of clock pulses to complete its operation transparently for the user.
However, if too few bits are shifted between each Update-DR state during page load, the TAP
controller should stay in the Run-Test/Idle state for some TCK cycles to ensure that there are at
least 11 TCK cycles between each Update-DR state.
27.8.12 Programming Algorithm
All references below of type “1a”, “1b”, and so on, refer to Table 27-16.
27.8.13 Entering Programming Mode
1. Enter JTAG instruction AVR_RESET and shift 1 in the Reset Register.
2. Enter instruction PROG_ENABLE and shift 0b1010_0011_0111_0000 in the Program-
ming Enable Register.
27.8.14 Leaving Programming Mode
1. Enter JTAG instruction PROG_COMMANDS.
2. Disable all programming instructions by using no operation instruction 11a.
3. Enter instruction PROG_ENABLE and shift 0b0000_0000_0000_0000 in the program-
ming Enable Register.
4. Enter JTAG instruction AVR_RESET and shift 0 in the Reset Register.
TDI
TDO
D
A
T
A
Flash
EEPROM
Fuses
Lock Bits
STROBES
ADDRESS
State
Machine
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27.8.15 Performing Chip Erase
1. Enter JTAG instruction PROG_COMMANDS.
2. Start Chip Erase using programming instruction 1a.
3. Poll for Chip Erase complete using programming instruction 1b, or wait for tWLRH_CE (refer
to Table 27-12 on page 307).
27.8.16 Programming the Flash
Before programming the Flash a Chip Erase must be performed, see “Performing Chip Erase”
on page 323.
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Flash write using programming instruction 2a.
3. Load address High byte using programming instruction 2b.
4. Load address Low byte using programming instruction 2c.
5. Load data using programming instructions 2d, 2e and 2f.
6. Repeat steps 4 and 5 for all instruction words in the page.
7. Write the page using programming instruction 2g.
8. Poll for Flash write complete using programming instruction 2h, or wait for tWLRH (refer to
Table 27-12 on page 307).
9. Repeat steps 3 to 7 until all data have been programmed.
A more efficient data transfer can be achieved using the PROG_PAGELOAD instruction:
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Flash write using programming instruction 2a.
3. Load the page address using programming instructions 2b and 2c. PCWORD (refer to
Table 27-10 on page 298) is used to address within one page and must be written as 0.
4. Enter JTAG instruction PROG_PAGELOAD.
5. Load the entire page by shifting in all instruction words in the page byte-by-byte, starting
with the LSB of the first instruction in the page and ending with the MSB of the last
instruction in the page. Use Update-DR to copy the contents of the Flash Data Byte Reg-
ister into the Flash page location and to auto-increment the Program Counter before
each new word.
6. Enter JTAG instruction PROG_COMMANDS.
7. Write the page using programming instruction 2g.
8. Poll for Flash write complete using programming instruction 2h, or wait for tWLRH (refer to
Table 27-12 on page 307).
9. Repeat steps 3 to 8 until all data have been programmed.
27.8.17 Reading the Flash
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Flash read using programming instruction 3a.
3. Load address using programming instructions 3b and 3c.
4. Read data using programming instruction 3d.
5. Repeat steps 3 and 4 until all data have been read.
A more efficient data transfer can be achieved using the PROG_PAGEREAD instruction:
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Flash read using programming instruction 3a.
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3. Load the page address using programming instructions 3b and 3c. PCWORD (refer to
Table 27-10 on page 298) is used to address within one page and must be written as 0.
4. Enter JTAG instruction PROG_PAGEREAD.
5. Read the entire page (or Flash) by shifting out all instruction words in the page (or Flash),
starting with the LSB of the first instruction in the page (Flash) and ending with the MSB
of the last instruction in the page (Flash). The Capture-DR state both captures the data
from the Flash, and also auto-increments the program counter after each word is read.
Note that Capture-DR comes before the shift-DR state. Hence, the first byte which is
shifted out contains valid data.
6. Enter JTAG instruction PROG_COMMANDS.
7. Repeat steps 3 to 6 until all data have been read.
27.8.18 Programming the EEPROM
Before programming the EEPROM a Chip Erase must be performed, see “Performing Chip
Erase” on page 323.
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable EEPROM write using programming instruction 4a.
3. Load address High byte using programming instruction 4b.
4. Load address Low byte using programming instruction 4c.
5. Load data using programming instructions 4d and 4e.
6. Repeat steps 4 and 5 for all data bytes in the page.
7. Write the data using programming instruction 4f.
8. Poll for EEPROM write complete using programming instruction 4g, or wait for tWLRH
(refer to Table 27-12 on page 307).
9. Repeat steps 3 to 8 until all data have been programmed.
Note that the PROG_PAGELOAD instruction can not be used when programming the EEPROM.
27.8.19 Reading the EEPROM
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable EEPROM read using programming instruction 5a.
3. Load address using programming instructions 5b and 5c.
4. Read data using programming instruction 5d.
5. Repeat steps 3 and 4 until all data have been read.
Note that the PROG_PAGEREAD instruction can not be used when reading the EEPROM.
27.8.20 Programming the Fuses
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Fuse write using programming instruction 6a.
3. Load data high byte using programming instructions 6b. A bit value of “0” will program the
corresponding fuse, a “1” will unprogram the fuse.
4. Write Fuse High byte using programming instruction 6c.
5. Poll for Fuse write complete using programming instruction 6d, or wait for tWLRH (refer to
Table 27-12 on page 307).
6. Load data low byte using programming instructions 6e. A “0” will program the fuse, a “1”
will unprogram the fuse.
7. Write Fuse low byte using programming instruction 6f.
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8. Poll for Fuse write complete using programming instruction 6g, or wait for tWLRH (refer to
Table 27-12 on page 307).
27.8.21 Programming the Lock Bits
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Lock bit write using programming instruction 7a.
3. Load data using programming instructions 7b. A bit value of “0” will program the corre-
sponding lock bit, a “1” will leave the lock bit unchanged.
4. Write Lock bits using programming instruction 7c.
5. Poll for Lock bit write complete using programming instruction 7d, or wait for tWLRH (refer
to Table 27-12 on page 307).
Reading the Fuses
and Lock Bits
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Fuse/Lock bit read using programming instruction 8a.
3. To read all Fuses and Lock bits, use programming instruction 8e.
To only read Fuse High byte, use programming instruction 8b.
To only read Fuse Low byte, use programming instruction 8c.
To only read Lock bits, use programming instruction 8d.
Reading the Signature
Bytes
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Signature byte read using programming instruction 9a.
3. Load address 0x00 using programming instruction 9b.
4. Read first signature byte using programming instruction 9c.
5. Repeat steps 3 and 4 with address 0x01 and address 0x02 to read the second and third
signature bytes, respectively.
Reading the
Calibration Byte
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Calibration byte read using programming instruction 10a.
3. Load address 0x00 using programming instruction 10b.
Read the calibration byte using programming instruction 10c.
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28. Electrical Characteristics
28.1 Absolute Maximum Ratings*
28.2 DC Characteristics
Operating Temperature.................................. -55°C to +125°C*NOTICE: Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent dam-
age to the device. This is a stress rating only and
functional operation of the device at these or
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.
Storage Temperature ..................................... -65°C to +150°C
Voltage on any Pin except RESET
with respect to Ground ................................-0.5V to VCC+0.5V
Voltage on RESET with respect to Ground......-0.5V to +13.0V
Maximum Operating Voltage ............................................ 6.0V
DC Current per I/O Pin ................................................ 40.0mA
DC Current VCC and GND Pins................................. 200.0mA
Table 28-1. TA = -40°C to 85°C, VCC = 1.8V to 5.5V (unless otherwise noted)
Symbol Parameter Condition Min. Typ. Max. Units
VIL
Input Low Voltage, Except
XTAL1 pin
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
-0.5
-0.5
0.2VCC(1)
0.3VCC(1) V
VIL1
Input Low Voltage, XTAL1
pin VCC = 1.8V - 5.5V -0.5 0.1VCC(1) V
VIH
Input High Voltage,
Except XTAL1 and
RESET pins
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
0.7VCC(2)
0.6VCC(2)
VCC + 0.5
VCC + 0.5 V
VIH1
Input High Voltage,
XTAL1 pin
VCC = 1.8V - 2.4V
VCC = 2.4V - 5.5V
0.8VCC(2)
0.7VCC(2)
VCC + 0.5
VCC + 0.5 V
VIH2
Input High Voltage,
RESET pin VCC = 1.8V - 5.5V 0.85VCC(2) VCC + 0.5 V
VOL
Output Low Voltage(3),
Port A, C, D, E, F, G, H, J
IOL = 10mA, VCC = 5V
IOL = 5mA, VCC = 3V
0.7
0.5 V
VOL1
Output Low Voltage(3),
Port B
IOL = 20mA, VCC = 5V
IOL = 10mA, VCC = 3V
0.7
0.5 V
VOH
Output High Voltage(4),
Port A, C, D, E, F, G, H, J
IOH = -10mA, VCC = 5V
IOH = -5mA, VCC = 3V
4.2
2.3 V
VOH1
Output High Voltage(4),
Port B
IOH = -20mA, VCC = 5V
IOH = -10mA, VCC = 3V
4.2
2.3 V
IIL
Input Leakage
Current I/O Pin
VCC = 5.5V, pin low
(absolute value) 1µA
IIH
Input Leakage
Current I/O Pin
VCC = 5.5V, pin high
(absolute value) 1µA
RRST Reset Pull-up Resistor 20 100 kΩ
RPU I/O Pin Pull-up Resistor 20 100 kΩ
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Notes: 1. “Max” means the highest value where the pin is guaranteed to be read as low
2. “Min” means the lowest value where the pin is guaranteed to be read as high
3. Although each I/O port can sink more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V for Port B and 10mA at
VCC = 5V, 5mA at VCC = 3V for all other ports) under steady state conditions (non-transient), the following must be observed:
TQFP and QFN/MLF Package:
1] The sum of all IOL, for all ports, should not exceed 400 mA.
2] The sum of all IOL, for ports A0 - A7, C4 - C7, G2 should not exceed 100mA.
3] The sum of all IOL, for ports B0 - B7, E0 - E7, G3 - G5 should not exceed 100mA.
4] The sum of all IOL, for ports D0 - D7, C0 - C3, G0 - G1 should not exceed 100mA.
5] The sum of all IOL, for ports F0 - F7, should not exceed 100mA.
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater
than the listed test condition.
4. Although each I/O port can source more than the test conditions (20 mA at VCC = 5V, 10 mA at VCC = 3V for Port B and 10mA
at VCC = 5V, 5mA at VCC = 3V for all other ports) under steady state conditions (non-transient), the following must be
observed:
TQFP and QFN/MLF Package:
1] The sum of all IOL, for all ports, should not exceed 400mA.
2] The sum of all IOL, for ports A0 - A7, C4 - C7, G2 should not exceed 100mA.
3] The sum of all IOL, for ports B0 - B7, E0 - E7, G3 - G5 should not exceed 100mA.
4] The sum of all IOL, for ports D0 - D7, C0 - C3, G0 - G1 should not exceed 100mA.
5] The sum of all IOL, for ports F0 - F7, should not exceed 100 mA.
If IOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current
greater than the listed test condition.
5. Typical values at 25°C.
ICC
Power Supply Current
Active 1MHz, VCC = 2V 1.5 mA
Active 4MHz, VCC = 3V 3.5 mA
Active 8MHz, VCC = 5V 12 mA
Idle 1MHz, VCC = 2V 0.45 mA
Idle 4MHz, VCC = 3V 1.5 mA
Idle 8MHz, VCC = 5V 5.5 mA
Power-down mode(5) WDT enabled, VCC = 3V 7 15 µA
WDT disabled, VCC = 3V 0.25 2 µA
VACIO
Analog Comparator
Input Offset Voltage
VCC = 5V
Vin = VCC/2 <10 40 mV
IACLK
Analog Comparator
Input Leakage Current
VCC = 5V
Vin = VCC/2 -50 50 nA
tACID
Analog Comparator
Propagation Delay
VCC = 2.7V
VCC = 4.0V
750
500 ns
Table 28-1. TA = -40°C to 85°C, VCC = 1.8V to 5.5V (unless otherwise noted) (Continued)
Symbol Parameter Condition Min. Typ. Max. Units
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28.3 Speed Grades
Figure 28-1. Maximum Frequency vs. VCC (4 - 8MHz).
Figure 28-2. Maximum Frequency vs. VCC (8 - 16MHz).
8 MHz
4 MHz
1.8V 2.7V 5.5V
Safe Operating Area
16 MHz
8 MHz
2.7V 4.5V 5.5V
Safe Operating Area
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28.4 Clock Characteristics
28.4.1 Calibrated Internal RC Oscillator Accuracy
Notes: 1. Voltage range for ATmega329V/3290V/649V/6490V.
2. Voltage range for ATmega329/3290/649/6490.
28.4.2 External Clock Drive Waveforms
Figure 28-3. External Clock Drive Waveforms
28.4.3 External Clock Drive
Table 28-2. Calibration Accuracy of Internal RC Oscillator
Frequency VCC Temperature Calibration Accuracy
Factory Calibration 8.0MHz 3V 25°C±10%
User
Calibration 7.3 - 8.1MHz 1.8V - 5.5V(1)
2.7V - 5.5V(2) -40°C - 85°C±1%
V
IL1
V
IH1
Table 28-3. External Clock Drive
Symbol Parameter
VCC=1.8-5.5V VCC=2.7-5.5V VCC=4.5-5.5V
UnitsMin. Max. Min. Max. Min. Max.
1/tCLCL
Oscillator
Frequency 0408016MHz
tCLCL Clock Period 1000 125 62.5 ns
tCHCX High Time 400 50 25 ns
tCLCX Low Time 400 50 25 ns
tCLCH Rise Time 2.0 1.6 0.5 μs
tCHCL Fall Time 2.0 1.6 0.5 μs
ΔtCLCL
Change in period
from one clock
cycle to the next
22 2%
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28.5 System and Reset Characteristics
Notes: 1. The Power-on Reset will not work unless the supply voltage has been below VPOT (falling)
Notes: 1. VBOT may be below nominal minimum operating voltage for some devices. For devices where this is the case, the device is
tested down to VCC = VBOT during the production test. This guarantees that a Brown-Out Reset will occur before VCC drops to
a voltage where correct operation of the microcontroller is no longer guaranteed. The test is performed using
BODLEVEL = 10 for ATmega329/3290/649/6490V and BODLEVEL = 01 for ATmega329/3290/649/6490L.
Table 28-4. Reset, Brown-out, and Internal Voltage Reference Characteristics
Symbol Parameter Condition Min Typ Max Units
VPOT
Power-on Reset Threshold Voltage (rising) TA = -40°C to
85°C 0.7 1.0 1.4 V
Power-on Reset Threshold Voltage
(falling)(1)
TA = -40°C to
85°C 0.05 0.9 1.3 V
VPSR Power-on Slope Rate 0.01 4.5 V/ms
VRST RESET Pin Threshold Voltage VCC = 3V 0.2 VCC 0.85 VCC V
tRST Minimum pulse width on RESET Pin VCC = 3V 800 ns
VHYST Brown-out Detector Hysteresis 50 mV
tBOD Min Pulse Width on Brown-out Reset 2 µs
VBG
Bandgap reference voltage VCC = 2.7V,
TA= 25°C 1.0 1.1 1.2 V
tBG
Bandgap reference start-up time VCC = 2.7V,
TA= 25°C 40 70 µs
IBG
Bandgap reference current consumption VCC = 2.7V,
TA= 25°C 15 µA
Table 28-5. BODLEVEL Fuse Coding(1)
BODLEVEL 1:0 Fuses Min VBOT Typ VBOT Max VBOT Units
11 BOD Disabled
10 1.7 1.82.0
V01 2.5 2.7 2.9
00 4.1 4.3 4.5
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28.6 SPI Timing Characteristics
See Figure 28-4 and Figure 28-5 for details.
Note: 1. In SPI Programming mode the minimum SCK high/low period is:
- 2 tCLCL for fCK < 12MHz
- 3 tCLCL for fCK > 12MHz
Figure 28-4. SPI Interface Timing Requirements (Master Mode)
Table 28-6. SPI Timing Parameters
Description Mode Min Typ Max
1 SCK period Master See Table 18-5
ns
2 SCK high/low Master 50% duty cycle
3 Rise/Fall time Master 3.6
4 Setup Master 10
5HoldMaster 10
6 Out to SCK Master 0.5 • tsck
7 SCK to out Master 10
8SCK to out high Master 10
9SS
low to out Slave 15
10 SCK period Slave 4 • tck
11 SCK high/low(1) Slave 2 • tck
12 Rise/Fall time Slave 1.6 µs
13 Setup Slave 10
ns
14 Hold Slave tck
15 SCK to out Slave 15
16 SCK to SS high Slave 20
17 SS high to tri-state Slave 10
18SS low to SCK Slave 20 • tck
MOSI
(Data Output)
SCK
(CPOL = 1)
MISO
(Data Input)
SCK
(CPOL = 0)
SS
MSB LSB
LSBMSB
...
...
61
22
345
8
7
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Figure 28-5. SPI Interface Timing Requirements (Slave Mode)
MISO
(Data Output)
SCK
(CPOL = 1)
MOSI
(Data Input)
SCK
(CPOL = 0)
SS
MSB LSB
LSBMSB
...
...
10
11 11
1213 14
17
15
9
X
16
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28.7 ADC Characteristics
Table 28-7. ADC Characteristics
Symbol Parameter Condition Min Typ Max Units
Resolution Single Ended Conversion 10 Bits
Differential Conversion 8Bits
Absolute accuracy (Including
INL, DNL, quantization error,
gain and offset error)
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
22.5LSB
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 1MHz
4.5 LSB
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
Noise Reduction Mode
2LSB
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 1MHz
Noise Reduction Mode
4.5 LSB
Integral Non-Linearity (INL)
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
0.5 LSB
Differential Non-Linearity (DNL)
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
0.25 LSB
Gain Error
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
2LSB
Offset Error
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
2LSB
Conversion Time Free Running Conversion 13 260 µs
Clock Frequency Single Ended Conversion 50 1000 kHz
AVCC Analog Supply Voltage VCC - 0.3 VCC + 0.3 V
VREF Reference Voltage Single Ended Conversion 1.0 AVCC V
Differential Conversion 1.0 AVCC - 0.5 V
VIN
Pin Input Voltage Single Ended Channels GNDV
REF V
Differential Channels GNDAVCCV
Input Range Single Ended Channels GNDV
REF V
Differential Channels(1) -0.85VREF VREF V
Input Bandwidth Single Ended Channels 38.5 kHz
Differential Channels 4 kHz
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Note: 1. Voltage difference between channels.
28.8 LCD Controller Characteristics
VINTInternal Voltage Reference 1.0 1.1 1.2 V
RREF Reference Input Resistance 32 kΩ
RAINAnalog Input Resistance 100 MΩ
Table 28-8. LCD Controller Characteristics
Symbol Parameter Condition Min. Typ Max Units
ILCD LCD Driver Current Total for All COM and SEG pins 6 µA
RSEG Segment Driver Output Impedance 10 kΩ
RCOM Blackplane Driver Output Impedance 2 kΩ
Table 28-7. ADC Characteristics (Continued)
Symbol Parameter Condition Min Typ Max Units
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29. Typical Characteristics
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.
All Active- and Idle current consumption measurements are done with all bits in the PRR register
set and thus, the corresponding I/O modules are turned off. Also the Analog Comparator is dis-
abled during these measurements. See “Power Reduction Register” on page 37 for details.
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 tempera-
ture. 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 cur-
rent drawn by the Watchdog Timer.
29.0.1 Active Supply Current
Figure 29-1. Active Supply Current vs. Frequency (0.1 - 1.0MHz)
5.5 V
5.0 V
4.5 V
4.0 V
3.3 V
2.7 V
1.8 V
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 0.1 0.2 0.3 0.4
0.5
0.6 0.7 0.8 0.91
Frequency (MHz)
I
CC
(m A)
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Figure 29-2. Active Supply Current vs. Frequency (1 - 16MHz))
Figure 29-3. Active Supply Current vs. VCC (Internal RC Oscillator, 8MHz)
5.5 V
5.0 V
4.5 V
4.0 V
3.3 V
2.7 V
1.8 V
0
2
4
6
8
10
12
14
16
0246810121416
Frequency (MHz)
ICC (mA)
0
2
4
6
8
10
12
14
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(mA)
85
°C
25
°C
-40
°
C
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Figure 29-4. Active Supply Current vs. VCC
(Internal RC Oscillator, CKDIV8 Programmed, 1MHz)
Figure 29-5. Active Supply Current vs. VCC (32kHz External Oscillator)
0
0.5
1
1.5
2
2.5
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (mA)
85
°C
25
°C
-40
°C
85 °C
25 °C
-40 °C
0
10
20
30
40
50
60
70
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
ICC (u A )
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29.0.2 Idle Supply Current
Figure 29-6. Idle Supply Current vs. Frequency (0.1 - 1.0MHz)
Figure 29-7. Idle Supply Current vs. Frequency (1 - 16MHz)
5.5 V
5.0 V
4.5 V
4.0 V
3.3 V
2.7 V
1.8 V
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.91
Frequency (MHz)
I
CC
(mA)
5.5 V
5.0 V
4.5 V
4.0 V
3.3 V
2.7 V
0
1
2
3
4
5
6
0246810121416
Frequency (MHz)
I
CC
(mA)
1.8 V
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Figure 29-8. Idle Supply Current vs. VCC (Internal RC Oscillator, 8MHz)
Figure 29-9. Idle Supply Current vs. VCC (Internal RC Oscillator, CKDIV8 Programmed,
1MHz)
0
1
2
3
4
5
6
7
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(mA)
85
°C
25
°C
-40
°C
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(mA)
85 C
°
25 C
°
-40 C
°
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Figure 29-10. Idle Supply Current vs. VCC (32kHz External Oscillator)
29.0.3 Supply Current of I/O 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 “Power Reduction Register” on page 37 for
details.
It is possible to calculate the typical current consumption based on the numbers from Table 29-2
for other VCC and frequency settings than listed in Table 29-1.
85 °C
25 °C
-40 °C
0
5
10
15
20
25
30
35
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
Table 29-1. 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
PRADC 17µA 116µA 562µA
PRUSART0 9µA 59µA 248µA
PRSPI 10µA 62µA 257µA
PRTIM1 5µA 33µA 135µA
PRLCD 6µA 36µA 146µA
Table 29-2. Additional Current Consumption (percentage) in Active and Idle mode
PRR bit
Additional Current consumption
compared to Active with external
clock
(see Figure 29-1 and Figure 29-2)
Additional Current consumption
compared to Idle with external
clock
(see Figure 29-6 and Figure 29-7)
PRADC 5.4% 16.8%
PRUSART0 2.7% 8.5%
PRSPI 2.9% 9.0%
PRTIM1 1.5% 4.8%
PRLCD 1.7% 5.2%
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29.0.3.1 Example
Calculate the expected current consumption in idle mode with USART0, TIMER1, and SPI
enabled at VCC = 3.0V and F = 1MHz. Table 29-2 shows that we need to add 8.5% for the
USART0, 9% for the SPI, and 4.8% for the TIMER1 module. From Figure 29-6, we find that the
idle current consumption is ~0.16mA at VCC = 3.0V and F = 1MHz. The total current consump-
tion in idle mode with USART0, TIMER1, and SPI enabled, gives:
29.0.4 Power-down Supply Current
Figure 29-11. Power-down Supply Current vs. VCC (Watchdog Timer Disabled)
Figure 29-12. Power-down Supply Current vs. VCC (Watchdog Timer Enabled)
ICCtotal 0.16mA 10.0850.090.048+++()•0.20mA≈≈
85 °C
25 °C
-40 °C
0
0.5
1
1.5
2
2.5
3
3.5
4
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
ICC (uA)
85 °C
25 °C
-40 °C
0
2
4
6
8
10
12
14
16
18
20
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC
(V)
I
CC
(uA)
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29.0.5 Power-save Supply Current
Figure 29-13. Power-save Supply Current vs. VCC (Watchdog Timer Disabled)
29.0.6 Standby Supply Current
Figure 29-14. Standby Supply Current vs. VCC (Low Power Crystal Oscillator)
0
5
10
15
20
25
30
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (uA)
85°C
25°C
6MHz Xtal
6MHz Res.
4MHz Xtal
4MHz Res.
455kHz Res.
32kHz Xtal
2MHz Xtal
2MHz Res.
1MHz Res.
0
20
40
60
80
100
120
140
160
180
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
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29.0.7 Pin Pull-up
Figure 29-15. I/O Pin Pull-up Resistor Current vs. Input Voltage (VCC = 5V)
Figure 29-16. I/O Pin Pull-up Resistor Current vs. Input Voltage (VCC = 2.7V)
0
20
40
60
80
100
120
140
160
012345
V
IO
(V)
I
IO
(uA)
85
°C
25
°C
-40
°C
0
10
20
30
40
50
60
70
80
90
0 0.5 1 1.5 2 2.5 3
VIO (V)
IIO (uA)
85
°C
25
°C
-40
°C
344
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-17. I/O Pin Pull-up Resistor Current vs. Input Voltage (VCC = 1.8V)
Figure 29-18. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 5V)
0
10
20
30
40
50
60
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
VOP (V)
IOP (uA)
85
°C
25
°C
-40
°C
0
20
40
60
80
100
120
012345
VRESET (V)
IRESET (uA)
-40
°C
25
°C
85
°C
345
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-19. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 2.7V)
Figure 29-20. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 1.8V)
0
10
20
30
40
50
60
70
0 0.5 1 1.5 2 2.5 3
V
RESET
(V)
I
RESET
(uA)
-40
°C
25
°C
85
°C
0
5
10
15
20
25
30
35
40
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
V
RESET
(V)
I
RESET
(uA)
-40
°C
25
°C
85
°C
346
2552K–AVR–04/11
ATmega329/3290/649/6490
29.0.8 Pin Driver Strength
Figure 29-21. I/O Pin Source Current vs. Output Voltage, Ports A, C, D, E, F, G, H, J (VCC =5V)
Figure 29-22. I/O Pin Source Current vs. Output Voltage, Ports A, C, D, E, F, G, H, J
(VCC =2.7V)
0
10
20
30
40
50
60
70
0123456
V
OH
(V)
I
OH
(mA)
85
°C
25
°C
-40
°C
0
5
10
15
20
25
0 0.5 1 1.5 2 2.5 3
V
OH
(V)
I
OH
(mA)
85
°C
25
°C
-40
°C
347
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-23. I/O Pin Source Current vs. Output Voltage, Ports A, C, D, E, F, G, H, J
(VCC =1.8V)
Figure 29-24. I/O Pin Source Current vs. Output Voltage, Port B (VCC= 5V)
0
1
2
3
4
5
6
7
8
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
VOH (V)
IOH (mA)
85
°C
25
°C
-40
°C
0
10
20
30
40
50
60
70
80
01234
V
OH
(V)
I
OH
(mA)
85
°C
25
°C
-40
°C
348
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-25. I/O Pin Source Current vs. Output Voltage, Port B (VCC = 2.7V)
Figure 29-26. I/O Pin Source Current vs. Output Voltage, Port B (VCC = 1.8V)
0
5
10
15
20
25
30
35
0 0.5 1 1.5 2 2.5 3
V
OH
(V)
I
OH
(mA)
85°C
25°C
-40°C
0
1
2
3
4
5
6
7
8
9
10
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
V
OH
(V)
I
OH
(mA)
85°C
25°C
-40°C
349
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-27. I/O Pin Sink Current vs. Output Voltage, Ports A, C, D, E, F, G, H, J
(VCC = 5V)
Figure 29-28. I/O Pin Sink Current vs. Output Voltage, Ports A, C, D, E, F, G, H, J
(VCC = 2.7V)
0
5
10
15
20
25
30
35
40
45
50
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
VOL (V)
IOL (mA)
85
°C
25
°C
-40
°C
0
2
4
6
8
10
12
14
16
18
20
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
V
OL
(V)
I
OL
(mA)
85°C
25°C
-40°C
350
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-29. I/O Pin Sink Current vs. Output Voltage, Ports A, C, D, E, F, G, H, J
(VCC = 1.8V)
Figure 29-30. I/O Pin Sink Current vs. Output Voltage, Port B (VCC = 5V)
0
1
2
3
4
5
6
7
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
V
OL
(V)
I
OL
(mA)
85
°C
25
°C
-40
°C
0
10
20
30
40
50
60
70
80
90
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
V
OL
(V)
I
OL
(mA)
85
°C
25
°C
-40
°C
351
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-31. I/O Pin Sink Current vs. Output Voltage, Port B (VCC = 2.7V)
Figure 29-32. I/O Pin Sink Current vs. Output Voltage, Port B (VCC = 1.8V)
0
5
10
15
20
25
30
35
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
V
OL
(V)
I
OL
(mA)
85
°C
25
°C
-40
°C
0
2
4
6
8
10
12
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
V
OL
(V)
I
OL
(mA)
85
°C
25
°C
-40
°C
352
2552K–AVR–04/11
ATmega329/3290/649/6490
29.0.9 Pin Thresholds and hysteresis
Figure 29-33. I/O Pin Input Threshold Voltage vs. VCC (VIH, I/O Pin Read as “1”)
Figure 29-34. I/O Pin Input Threshold Voltage vs. VCC (VIL, I/O Pin Read as “0”)
0
0.5
1
1.5
2
2.5
3
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
Threshold (V)
85
°
C
25
°
C
-40
°
C
0
0.5
1
1.5
2
2.5
3
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
Threshold (V)
85
°
C
25
°
C
-40
°
C
353
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-35. I/O Pin Input Hysteresis vs. VCC
Figure 29-36. Reset Input Threshold Voltage vs. VCC (VIH,Reset Pin Read as “1”)
0
0.1
0.2
0.3
0.4
0.5
0.6
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
85
°C
25
°C
-40
°C
Input Hysteresis (V)
0
0.5
1
1.5
2
2.5
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
Threshold (V)
85
°C
25
°C
-40
°C
354
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-37. Reset Input Threshold Voltage vs. VCC (VIL,Reset Pin Read as “0”)
Figure 29-38. Reset Input Pin Hysteresis vs. VCC
0
0.5
1
1.5
2
2.5
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
Threshold (V)
85
°
C
25
°
C
-40
°
C
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
Input Hysteresis (V)
85
°C
25
°C
-40
°C
355
2552K–AVR–04/11
ATmega329/3290/649/6490
29.0.10 BOD Thresholds and Analog Comparator Offset
Figure 29-39. BOD Thresholds vs. Temperature (BOD Level is 4.3V)
Figure 29-40. BOD Thresholds vs. Temperature (BOD Level is 2.7V)
Rising V
CC
Falling V
CC
4
4.1
4.2
4.3
4.4
4.5
4.6
-60 -40 -20 0 20 40 60 80 100
Temperature (°C)
Threshold (V)
Rising VCC
Falling V
CC
2.4
2.5
2.6
2.7
2.8
2.9
3
-60 -40 -20 0 20 40 60 80 100
Temperature (°C)
Threshol d ( V)
356
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-41. BOD Thresholds vs. Temperature (BOD Level is 1.8V)
Figure 29-42. Bandgap Voltage vs. VCC
1.7
1.75
1.8
1.85
1.9
1.95
-60 -40 -20 0 20 40 60 80 100
Temperature (°C)
Threshold (V)
Rising V
CC
Falling V
CC
85°C
25°C
-40°C
1.068
1.069
1.07
1.071
1.072
1.073
1.074
1.075
1.076
1.5 2 2.5 3 3.5 4 4.5 5
V
CC
(V)
Bandgap Voltage (V)
357
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-43. Analog Comparator Offset Voltage vs. Common Mode Voltage (VCC = 5V)
Figure 29-44. Analog Comparator Offset Voltage vs. Common Mode Voltage (VCC =2.7V)
85°C
25°C
-40°C
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Common Mode Voltage (V)
Comparator Offset Voltage (V)
85°C
25°C
-40°C
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0 0.5 1 1.5 2 2.5 3
Common Mode Voltage (V)
Comparator Offset Voltage (V)
358
2552K–AVR–04/11
ATmega329/3290/649/6490
29.0.11 Internal Oscillator Speed
Figure 29-45. Watchdog Oscillator Frequency vs. VCC
Figure 29-46. Calibrated 8MHz RC Oscillator Frequency vs. Temperature
85 °C
25 °C
-40 °C
1000
1050
1100
1150
1200
1250
1300
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
F
RC
(kHz)
5.5 V
4.5 V
3.3 V
2.7 V
1.8 V
7.2
7.4
7.6
7.8
8
8.2
8.4
8.6
-60 -40 -20 0 20 40 60 80 100
Temperature (°C)
F
RC
(M Hz)
359
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-47. Calibrated 8MHz RC Oscillator Frequency vs. VCC
Figure 29-48. Calibrated 8MHz RC Oscillator Frequency vs. Osccal Value
85 °C
25 °C
-40 °C
7.2
7.4
7.6
7.8
8
8.2
8.4
8.6
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
FRC (MHz)
85 °C
25 °C
-40 °C
4
6
8
10
12
14
16
0163248648096 112 128 144 160 176 192 208 224 240 256
OSCCAL VALUE
F
RC
(M Hz)
360
2552K–AVR–04/11
ATmega329/3290/649/6490
29.0.12 Current Consumption of Peripheral Units
Figure 29-49. Brownout Detector Current vs. VCC
Figure 29-50. ADC Current vs. VCC (AREF = AVCC)
85 °C
25 °C
-40 °C
0
5
10
15
20
25
30
35
40
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
0
50
100
150
200
250
300
350
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (uA)
85°
C
25°
C
-40°
C
361
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-51. AREF External Reference Current vs. VCC
Figure 29-52. 32kHz TOSC Current vs. VCC (Watchdog Timer Disabled)
0
20
40
60
80
100
120
140
160
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
IAREF (uA)
85°
C
25°
C
-40°
C
0
5
10
15
20
25
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (uA)
85
°C
25
°C
362
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-53. Watchdog Timer Current vs. VCC
Figure 29-54. Analog Comparator Current vs. VCC
0
2
4
6
8
10
12
14
16
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
85°
C
25°
C
-40°
C
0
20
40
60
80
100
120
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (uA)
85°C
25°C
-40°C
363
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-55. Programming Current vs. VCC
29.0.13 Current Consumption in Reset and Reset Pulsewidth
Figure 29-56. Reset Supply Current vs. VCC (0.1 - 1.0MHz, Excluding Current Through The
Reset Pull-up)
85 °C
25 °C
-40 °C
0
2
4
6
8
10
12
14
16
18
20
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(mA)
5.5 V
5.0 V
4.5 V
4.0 V
3.3 V
2.7 V
1.8 V
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.91
Frequency (MHz)
ICC (mA)
364
2552K–AVR–04/11
ATmega329/3290/649/6490
Figure 29-57. Reset Supply Current vs. VCC (1 - 16MHz, Excluding Current Through The Reset
Pull-up)
Figure 29-58. Reset Pulse Width vs. VCC
5.5 V
5.0 V
4.5 V
4.0 V
3.3 V
2.7 V
1.8 V
0
0.5
1
1.5
2
2.5
3
0246810121416
Frequency (MHz)
I
CC
(mA)
0
500
1000
1500
2000
2500
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
Pulsewidth (ns)
85
°C
25
°C
-40
°C
365
2552K–AVR–04/11
ATmega329/3290/649/6490
30. Register Summary
Note: Registers with bold type only available in ATmega3290/6490.
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
(0xFF) LCDDR19 SEG339 SEG338 SEG337 SEG336 SEG335 SEG334 SEG333 SEG332 244
(0xFE) LCDDR18SEG331 SEG330 SEG329 SEG328 SEG327 SEG326 SEG325 SEG324 244
(0xFD) LCDDR17 SEG323 SEG322 SEG321 SEG320 SEG319 SEG318SEG317 SEG316 244
(0xFC) LCDDR16 SEG315 SEG314 SEG313 SEG312 SEG311 SEG310 SEG309 SEG308244
(0xFB) LCDDR15 SEG307 SEG306 SEG305 SEG304 SEG303 SEG302 SEG301 SEG300 244
(0xFA) LCDDR14 SEG239 SEG238 SEG237 SEG236 SEG235 SEG234 SEG233 SEG232 244
(0xF9) LCDDR13 SEG231 SEG230 SEG229 SEG228 SEG227 SEG226 SEG225 SEG224 244
(0xF8)LCDDR12 SEG223 SEG222 SEG221 SEG220 SEG219 SEG218SEG217 SEG216 244
(0xF7) LCDDR11 SEG215 SEG214 SEG213 SEG212 SEG211 SEG210 SEG209 SEG208244
(0xF6) LCDDR10 SEG207 SEG206 SEG205 SEG204 SEG203 SEG202 SEG201 SEG200 244
(0xF5) LCDDR09 SEG139 SEG138 SEG137 SEG136 SEG135 SEG134 SEG133 SEG132 244
(0xF4) LCDDR08SEG131 SEG130 SEG129 SEG128 SEG127 SEG126 SEG125 SEG124 244
(0xF3) LCDDR07 SEG123 SEG122 SEG121 SEG120 SEG119 SEG118SEG117 SEG116 244
(0xF2) LCDDR06 SEG115 SEG114 SEG113 SEG112 SEG111 SEG110 SEG109 SEG108244
(0xF1) LCDDR05 SEG107 SEG106 SEG105 SEG104 SEG103 SEG102 SEG101 SEG100 244
(0xF0) LCDDR04 SEG039 SEG038 SEG037 SEG036 SEG035 SEG034 SEG033 SEG032 244
(0xEF) LCDDR03 SEG031 SEG030 SEG029 SEG028 SEG027 SEG026 SEG025 SEG024 244
(0xEE) LCDDR02 SEG023 SEG022 SEG021 SEG020 SEG019 SEG018SEG017 SEG016 244
(0xED) LCDDR01 SEG015 SEG014 SEG013 SEG012 SEG011 SEG010 SEG009 SEG008244
(0xEC) LCDDR00 SEG007 SEG006 SEG005 SEG004 SEG003 SEG002 SEG001 SEG000 244
(0xEB) Reserved --------
(0xEA) Reserved --------
(0xE9) Reserved --------
(0xE8)Reserved --------
(0xE7) LCDCCR LCDDC2 LCDDC1 LCDDC0 - LCDCC3 LCDCC2 LCDCC1 LCDCC0 243
(0xE6) LCDFRR - LCDPS2 LCDPS1 LCDPS0 - LCDCD2 LCDCD1 LCDCD0 241
(0xE5) LCDCRB LCDCS LCD2B LCDMUX1 LCDMUX0 LCDPM3 LCDPM2 LCDPM1 LCDPM0 239
(0xE4) LCDCRA LCDEN LCDAB - LCDIF LCDIE --LCDBL239
(0xE3) Reserved --------
(0xE2) Reserved --------
(0xE1) Reserved --------
(0xE0) Reserved --------
(0xDF) Reserved --------
(0xDE) Reserved --------
(0xDD) PORTJ -PORTJ6 PORTJ5 PORTJ4 PORTJ3 PORTJ2 PORTJ1 PORTJ0 90
(0xDC) DDRJ -DDJ6 DDJ5 DDJ4 DDJ3 DDJ2 DDJ1 DDJ0 90
(0xDB) PINJ -PINJ6 PINJ5 PINJ4 PINJ3 PINJ2 PINJ1 PINJ0 90
(0xDA) PORTH PORTH7 PORTH6 PORTH5 PORTH4 PORTH3 PORTH2 PORTH1 PORTH0 89
(0xD9) DDRH DDH7 DDH6 DDH5 DDH4 DDH3 DDH2 DDH1 DDH0 90
(0xD8)PINH PINH7 PINH6 PINH5 PINH4 PINH3 PINH2 PINH1 PINH0 90
(0xD7) Reserved --------
(0xD6) Reserved --------
(0xD5) Reserved --------
(0xD4) Reserved --------
(0xD3) Reserved --------
(0xD2) Reserved --------
(0xD1) Reserved --------
(0xD0) Reserved --------
(0xCF) Reserved --------
(0xCE) Reserved --------
(0xCD) Reserved --------
(0xCC) Reserved --------
(0xCB) Reserved --------
(0xCA) Reserved --------
(0xC9) Reserved --------
(0xC8)Reserved --------
(0xC7) Reserved --------
(0xC6) UDR0 USART0 Data Register 190
(0xC5) UBRR0H USART0 Baud Rate Register High 194
(0xC4) UBRR0L USART0 Baud Rate Register Low 194
366
2552K–AVR–04/11
ATmega329/3290/649/6490
(0xC3) Reserved --------
(0xC2) UCSR0C - UMSEL0 UPM01 UPM00 USBS0 UCSZ01 UCSZ00 UCPOL0 192
(0xC1) UCSR0B RXCIE0 TXCIE0 UDRIE0 RXEN0TXEN0 UCSZ02 RXB80TXB80191
(0xC0) UCSR0A RXC0 TXC0 UDRE0 FE0 DOR0 UPE0 U2X0 MPCM0 190
(0xBF) Reserved --------
(0xBE) Reserved --------
(0xBD) Reserved --------
(0xBC) Reserved --------
(0xBB) Reserved --------
(0xBA) USIDR USI Data Register 203
(0xB9) USISR USISIF USIOIF USIPF USIDC USICNT3 USICNT2 USICNT1 USICNT0 203
(0xB8)USICR USISIE USIOIE USIWM1 USIWM0 USICS1 USICS0 USICLK USITC 204
(0xB7) Reserved --------
(0xB6) ASSR --- EXCLK AS2 TCN2UB OCR2UB TCR2UB 155
(0xB5) Reserved --------
(0xB4) Reserved --------
(0xB3) OCR2A Timer/Counter 2 Output Compare Register A 155
(0xB2) TCNT2 Timer/Counter2 155
(0xB1) Reserved --------
(0xB0) TCCR2A FOC2A WGM20 COM2A1 COM2A0 WGM21 CS22 CS21 CS20 153
(0xAF) Reserved --------
(0xAE) Reserved --------
(0xAD) Reserved --------
(0xAC) Reserved --------
(0xAB) Reserved --------
(0xAA) Reserved --------
(0xA9) Reserved --------
(0xA8)Reserved --------
(0xA7) Reserved --------
(0xA6) Reserved --------
(0xA5) Reserved --------
(0xA4) Reserved --------
(0xA3) Reserved --------
(0xA2) Reserved --------
(0xA1) Reserved --------
(0xA0) Reserved --------
(0x9F) Reserved --------
(0x9E) Reserved --------
(0x9D) Reserved --------
(0x9C) Reserved --------
(0x9B) Reserved --------
(0x9A) Reserved --------
(0x99) Reserved --------
(0x98)Reserved --------
(0x97) Reserved --------
(0x96) Reserved --------
(0x95) Reserved --------
(0x94) Reserved --------
(0x93) Reserved --------
(0x92) Reserved --------
(0x91) Reserved --------
(0x90) Reserved --------
(0x8F) Reserved --------
(0x8E) Reserved --------
(0x8D) Reserved --------
(0x8C) Reserved --------
(0x8B) OCR1BH Timer/Counter1 Output Compare Register B High 136
(0x8A) OCR1BL Timer/Counter1 Output Compare Register B Low 136
(0x89) OCR1AH Timer/Counter1 Output Compare Register A High 136
(0x88)OCR1AL Timer/Counter1 Output Compare Register A Low 136
(0x87) ICR1H Timer/Counter1 Input Capture Register High 137
(0x86) ICR1L Timer/Counter1 Input Capture Register Low 137
(0x85) TCNT1H Timer/Counter1 High 136
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
367
2552K–AVR–04/11
ATmega329/3290/649/6490
(0x84) TCNT1L Timer/Counter1 Low 136
(0x83) Reserved --------
(0x82) TCCR1C FOC1A FOC1B ------135
(0x81) TCCR1B ICNC1 ICES1 - WGM13WGM12CS12CS11CS10 134
(0x80) TCCR1A COM1A1 COM1A0 COM1B1 COM1B0 --WGM11WGM10132
(0x7F) DIDR1 ------AIN1D AIN0D 210
(0x7E) DIDR0 ADC7D ADC6D ADC5D ADC4D ADC3D ADC2D ADC1D ADC0D 227
(0x7D) Reserved --------
(0x7C) ADMUX REFS1 REFS0 ADLAR MUX4 MUX3 MUX2 MUX1 MUX0 223
(0x7B) ADCSRB -ACME- - - ADTS2 ADTS1 ADTS0 209/227
(0x7A) ADCSRA ADEN ADSC ADATE ADIF ADIE ADPS2 ADPS1 ADPS0 225
(0x79) ADCH ADC Data Register High 226
(0x78)ADCL ADC Data Register Low 226
(0x77) Reserved --------
(0x76) Reserved --------
(0x75) Reserved --------
(0x74) Reserved --------
(0x73) PCMSK3 -PCINT30 PCINT29 PCINT28 PCINT27 PCINT26 PCINT25 PCINT24 57
(0x72) Reserved --------
(0x71) Reserved --------
(0x70) TIMSK2 ------ OCIE2A TOIE2 156
(0x6F) TIMSK1 --ICIE1-- OCIE1B OCIE1A TOIE1 137
(0x6E) TIMSK0 ------ OCIE0A TOIE0 106
(0x6D) PCMSK2 PCINT23 PCINT22 PCINT21 PCINT20 PCINT19 PCINT18 PCINT17 PCINT16 57
(0x6C) PCMSK1 PCINT15 PCINT14 PCINT13 PCINT12 PCINT11 PCINT10 PCINT9 PCINT858
(0x6B) PCMSK0 PCINT7 PCINT6 PCINT5 PCINT4 PCINT3 PCINT2 PCINT1 PCINT0 58
(0x6A) Reserved --------
(0x69) EICRA ------ISC01ISC0055
(0x68)Reserved --------
(0x67) Reserved --------
(0x66) OSCCAL Oscillator Calibration Register [CAL7..0] 32
(0x65) Reserved --------
(0x64) PRR --- PRLCD PRTIM1 PRSPI PSUSART0 PRADC 40
(0x63) Reserved --------
(0x62) Reserved --------
(0x61) CLKPR CLKPCE --- CLKPS3 CLKPS2 CLKPS1 CLKPS0 33
(0x60) WDTCR --- WDCE WDE WDP2 WDP1 WDP0 48
0x3F (0x5F) SREG I T H S V NZC12
0x3E (0x5E) SPH Stack Pointer High 14
0x3D (0x5D) SPL Stack Pointer Low 14
0x3C (0x5C) Reserved --------
0x3B (0x5B) Reserved --------
0x3A (0x5A) Reserved --------
0x39 (0x59) Reserved --------
0x38 (0x58)Reserved --------
0x37 (0x57) SPMCSR SPMIE RWWSB - RWWSRE BLBSET PGWRT PGERS SPMEN291
0x36 (0x56) Reserved
0x35 (0x55) MCUCR JTD - -PUD--IVSELIVCE52/87/254
0x34 (0x54) MCUSR --- JTRF WDRF BORF EXTRF PORF 47
0x33 (0x53) SMCR ---- SM2 SM1 SM0 SE 39
0x32 (0x52) Reserved --------
0x31 (0x51) OCDR IDRD/OCDR7 OCDR6 OCDR5 OCDR4 OCDR3 OCDR2 OCDR1 OCDR0 250
0x30 (0x50) ACSR ACD ACBG ACO ACI ACIE ACIC ACIS1 ACIS0 209
0x2F (0x4F) Reserved --------
0x2E (0x4E) SPDR SPI Data Register 167
0x2D (0x4D) SPSR SPIF WCOL ----- SPI2X 167
0x2C (0x4C) SPCR SPIE SPE DORD MSTR CPOL CPHA SPR1 SPR0 165
0x2B (0x4B) GPIOR2 General Purpose I/O Register 25
0x2A (0x4A) GPIOR1 General Purpose I/O Register 25
0x29 (0x49) Reserved --------
0x28 (0x48)Reserved --------
0x27 (0x47) OCR0A Timer/Counter0 Output Compare A 105
0x26 (0x46) TCNT0 Timer/Counter0 105
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
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2552K–AVR–04/11
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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 AVRs, the CBI and SBI
instructions will only operate on the specified bit, and can therefore be used on registers containing such Status Flags. The
CBI and SBI instructions work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing I/O
Registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The
ATmega329/3290/649/6490 is a complex microcontroller with more peripheral units than can be supported within the 64
location reserved in Opcode for the IN and OUT instructions. For the Extended I/O space from 0x60 - 0xFF in SRAM, only
the ST/STS/STD and LD/LDS/LDD instructions can be used.
0x25 (0x45) Reserved --------
0x24 (0x44) TCCR0A FOC0A WGM00 COM0A1 COM0A0 WGM01 CS02 CS01 CS00 103
0x23 (0x43) GTCCR TSM ----- PSR2 PSR10 108/157
0x22 (0x42) EEARH ----- EEPROM Address Register High 22
0x21 (0x41) EEARL EEPROM Address Register Low 22
0x20 (0x40) EEDR EEPROM Data Register 22
0x1F (0x3F) EECR ---- EERIE EEMWE EEWE EERE 22
0x1E (0x3E) GPIOR0 General Purpose I/O Register 25
0x1D (0x3D) EIMSK PCIE3 PCIE2 PCIE1 PCIE0 ---INT0 55
0x1C (0x3C) EIFR PCIF3 PCIF2 PCIF1 PCIF0 - - -INTF0 56
0x1B (0x3B) Reserved --------
0x1A (0x3A) Reserved --------
0x19 (0x39) Reserved --------
0x18 (0x38)Reserved --------
0x17 (0x37) TIFR2 ------OCF2ATOV2157
0x16 (0x36) TIFR1 --ICF1--OCF1BOCF1ATOV1138
0x15 (0x35) TIFR0 ------OCF0ATOV0106
0x14 (0x34) PORTG --- PORTG4 PORTG3 PORTG2 PORTG1 PORTG0 89
0x13 (0x33) DDRG --- DDG4 DDG3 DDG2 DDG1 DDG0 89
0x12 (0x32) PING - -PING5 PING4 PING3 PING2 PING1 PING0 89
0x11 (0x31) PORTF PORTF7 PORTF6 PORTF5 PORTF4 PORTF3 PORTF2 PORTF1 PORTF0 89
0x10 (0x30) DDRF DDF7 DDF6 DDF5 DDF4 DDF3 DDF2 DDF1 DDF0 89
0x0F (0x2F) PINFPINF7 PINF6 PINF5 PINF4 PINF3 PINF2 PINF1 PINF0 89
0x0E (0x2E) PORTE PORTE7 PORTE6 PORTE5 PORTE4 PORTE3 PORTE2 PORTE1 PORTE0 88
0x0D (0x2D) DDRE DDE7 DDE6 DDE5 DDE4 DDE3 DDE2 DDE1 DDE0 88
0x0C (0x2C) PINEPINE7 PINE6 PINE5 PINE4 PINE3 PINE2 PINE1 PINE0 89
0x0B (0x2B) PORTD PORTD7 PORTD6 PORTD5 PORTD4 PORTD3 PORTD2 PORTD1 PORTD0 88
0x0A (0x2A) DDRD DDD7 DDD6 DDD5 DDD4 DDD3 DDD2 DDD1 DDD0 88
0x09 (0x29) PINDPIND7 PIND6 PIND5 PIND4 PIND3 PIND2 PIND1 PIND0 88
0x08 (0x28)PORTC PORTC7 PORTC6 PORTC5 PORTC4 PORTC3 PORTC2 PORTC1 PORTC0 88
0x07 (0x27) DDRC DDC7 DDC6 DDC5 DDC4 DDC3 DDC2 DDC1 DDC0 88
0x06 (0x26) PINCPINC7 PINC6 PINC5 PINC4 PINC3 PINC2 PINC1 PINC0 88
0x05 (0x25) PORTB PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 87
0x04 (0x24) DDRB DDB7 DDB6 DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 87
0x03 (0x23) PINBPINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 87
0x02 (0x22) PORTA P ORTA 7 PORTA6 PORTA5 PORTA4 PORTA3 P O RTA2 P O RTA 1 P O RTA 0 87
0x01 (0x21) DDRA DDA7 DDA6 DDA5 DDA4 DDA3 DDA2 DDA1 DDA0 87
0x00 (0x20) PINAPINA7 PINA6 PINA5 PINA4 PINA3 PINA2 PINA1 PINA0 87
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
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ATmega329/3290/649/6490
31. Instruction Set Summary
Mnemonics Operands Description Operation Flags #Clocks
ARITHMETIC AND LOGIC INSTRUCTIONS
ADD Rd, Rr Add two Registers Rd ← Rd + Rr Z,C,N,V,H 1
ADC Rd, Rr Add with Carry two Registers Rd ← Rd + Rr + C Z,C,N,V,H 1
ADIW Rdl,K Add Immediate to Word Rdh:Rdl ← Rdh:Rdl + K Z,C,N,V,S 2
SUB Rd, Rr Subtract two Registers Rd ← Rd - Rr Z,C,N,V,H 1
SUBI Rd, K Subtract Constant from Register Rd ← Rd - K Z,C,N,V,H 1
SBC Rd, Rr Subtract with Carry two Registers Rd ← Rd - Rr - C Z,C,N,V,H 1
SBCI Rd, K Subtract with Carry Constant from Reg. Rd ← Rd - K - C Z,C,N,V,H 1
SBIW Rdl,K Subtract Immediate from Word Rdh:Rdl ← Rdh:Rdl - K Z,C,N,V,S 2
AND Rd, Rr Logical AND Registers Rd ← Rd • Rr Z,N,V 1
ANDI Rd, K Logical AND Register and Constant Rd ← Rd • KZ,N,V 1
OR Rd, Rr Logical OR Registers Rd ← Rd v Rr Z,N,V 1
ORI Rd, K Logical OR Register and Constant Rd ← Rd v K Z,N,V 1
EOR Rd, Rr Exclusive OR Registers Rd ← Rd ⊕ Rr Z,N,V 1
COM Rd One’s Complement Rd ← 0xFF − Rd Z,C,N,V 1
NEG Rd Two’s Complement Rd ← 0x00 − Rd Z,C,N,V,H 1
SBR Rd,K Set Bit(s) in Register Rd ← Rd v K Z,N,V 1
CBR Rd,K Clear Bit(s) in Register Rd ← Rd • (0xFF - K) Z,N,V 1
INC Rd Increment Rd ← Rd + 1 Z,N,V 1
DEC Rd Decrement Rd ← Rd − 1 Z,N,V 1
TST Rd Test for Zero or Minus Rd ← Rd • Rd Z,N,V 1
CLR Rd Clear Register Rd ← Rd ⊕ Rd Z,N,V 1
SER Rd Set Register Rd ← 0xFF None 1
MUL Rd, Rr Multiply Unsigned R1:R0 ← Rd x Rr Z,C 2
MULS Rd, Rr Multiply Signed R1:R0 ← Rd x Rr Z,C 2
MULSU Rd, Rr Multiply Signed with Unsigned R1:R0 ← Rd x Rr Z,C 2
FMUL Rd, Rr Fractional Multiply Unsigned R1:R0 ← (Rd x Rr) << 1 Z,C 2
FMULS Rd, Rr Fractional Multiply Signed R1:R0 ← (Rd x Rr) << 1 Z,C 2
FMULSU Rd, Rr Fractional Multiply Signed with Unsigned R1:R0 ← (Rd x Rr) << 1 Z,C 2
BRANCH INSTRUCTIONS
RJMP k Relative Jump PC ← PC + k + 1 None 2
IJMP Indirect Jump to (Z) PC ← Z None 2
JMP k Direct Jump PC ← k None 3
RCALL k Relative Subroutine Call PC ← PC + k + 1 None 3
ICALL Indirect Call to (Z) PC ← Z None 3
CALL k Direct Subroutine Call PC ← k None 4
RET Subroutine Return PC ← STACK None 4
RETI Interrupt Return PC ← STACK I 4
CPSE Rd,Rr Compare, Skip if Equal if (Rd = Rr) PC ← PC + 2 or 3 None 1/2/3
CP Rd,Rr Compare Rd − Rr Z, N,V,C,H 1
CPC Rd,Rr Compare with Carry Rd − Rr − C Z, N,V,C,H 1
CPI Rd,K Compare Register with Immediate Rd − K Z, N,V,C,H 1
SBRC Rr, b Skip if Bit in Register Cleared if (Rr(b)=0) PC ← PC + 2 or 3 None 1/2/3
SBRS Rr, b Skip if Bit in Register is Set if (Rr(b)=1) PC ← PC + 2 or 3 None 1/2/3
SBIC P, b Skip if Bit in I/O Register Cleared if (P(b)=0) PC ← PC + 2 or 3 None 1/2/3
SBIS P, b Skip if Bit in I/O Register is Set if (P(b)=1) PC ← PC + 2 or 3 None 1/2/3
BRBS s, k Branch if Status Flag Set if (SREG(s) = 1) then PC←PC+k + 1 None 1/2
BRBC s, k Branch if Status Flag Cleared if (SREG(s) = 0) then PC←PC+k + 1 None 1/2
BREQ k Branch if Equal if (Z = 1) then PC ← PC + k + 1 None 1/2
BRNE k Branch if Not Equal if (Z = 0) then PC ← PC + k + 1 None 1/2
BRCS k Branch if Carry Set if (C = 1) then PC ← PC + k + 1 None 1/2
BRCC k Branch if Carry Cleared if (C = 0) then PC ← PC + k + 1 None 1/2
BRSH k Branch if Same or Higher if (C = 0) then PC ← PC + k + 1 None 1/2
BRLO k Branch if Lower if (C = 1) then PC ← PC + k + 1 None 1/2
BRMI k Branch if Minus if (N = 1) then PC ← PC + k + 1 None 1/2
BRPL k Branch if Plus if (N = 0) then PC ← PC + k + 1 None 1/2
BRGE k Branch if Greater or Equal, Signed if (N ⊕ V= 0) then PC ← PC + k + 1 None 1/2
BRLT k Branch if Less Than Zero, Signed if (N ⊕ V= 1) then PC ← PC + k + 1 None 1/2
BRHS k Branch if Half Carry Flag Set if (H = 1) then PC ← PC + k + 1 None 1/2
BRHC k Branch if Half Carry Flag Cleared if (H = 0) then PC ← PC + k + 1 None 1/2
BRTS k Branch if T Flag Set if (T = 1) then PC ← PC + k + 1 None 1/2
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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 s Flag Set SREG(s) ← 1 SREG(s) 1
BCLR s Flag 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 ← 1C1
CLC Clear Carry C ← 0 C 1
SENSet Negative Flag N ← 1 N1
CLNClear Negative Flag N ← 0 N1
SEZ Set Zero Flag Z ← 1Z1
CLZ Clear Zero Flag Z ← 0 Z 1
SEI Global Interrupt Enable I ← 1I1
CLI Global Interrupt Disable I ← 0 I 1
SES Set Signed Test Flag S ← 1S1
CLS Clear Signed Test Flag S ← 0 S 1
SEV Set Twos Complement Overflow. V ← 1V1
CLV Clear Twos Complement Overflow V ← 0 V 1
SET Set T in SREG T ← 1T1
CLT Clear T in SREG T ← 0 T 1
SEH Set Half Carry Flag in SREG H ← 1H1
CLH Clear Half Carry Flag in SREG H ← 0 H 1
DATA TRANSFER INSTRUCTIONS
MOV Rd, Rr Move Between Registers Rd ← Rr None 1
MOVW Rd, Rr Copy Register Word Rd+1:Rd ← Rr+1:Rr None 1
LDI Rd, K Load Immediate Rd ← K None 1
LD Rd, X Load Indirect Rd ← (X) None 2
LD Rd, X+ Load Indirect and Post-Inc. Rd ← (X), X ← X + 1 None 2
LD Rd, - X Load Indirect and Pre-Dec. X ← X - 1, Rd ← (X) None 2
LD Rd, Y Load Indirect Rd ← (Y) None 2
LD Rd, Y+ Load Indirect and Post-Inc. Rd ← (Y), Y ← Y + 1 None 2
LD Rd, - Y Load Indirect and Pre-Dec. Y ← Y - 1, Rd ← (Y) None 2
LDD Rd,Y+q Load Indirect with Displacement Rd ← (Y + q) None 2
LD Rd, Z Load Indirect Rd ← (Z) None 2
LD Rd, Z+ Load Indirect and Post-Inc. Rd ← (Z), Z ← Z+1 None 2
LD Rd, -Z Load Indirect and Pre-Dec. Z ← Z - 1, Rd ← (Z) None 2
LDD Rd, Z+q Load Indirect with Displacement Rd ← (Z + q) None 2
LDS Rd, k Load Direct from SRAM Rd ← (k) None 2
ST X, Rr Store Indirect (X) ← Rr None 2
ST X+, Rr Store Indirect and Post-Inc. (X) ← Rr, X ← X + 1 None 2
ST - X, Rr Store Indirect and Pre-Dec. X ← X - 1, (X) ← Rr None 2
ST Y, Rr 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 -
Mnemonics Operands Description Operation Flags #Clocks
371
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ATmega329/3290/649/6490
INRd, P In Port Rd ← P None 1
OUT P, Rr 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
Mnemonics Operands Description Operation Flags #Clocks
372
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ATmega329/3290/649/6490
32. Ordering Information
Notes: 1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging alternative, complies to the European Directive for Restriction of Hazardous Substances (RoHS direc-
tive). Also Halide free and fully Green.
3. For Speed vs. VCC see Figure 28-1 on page 328 and Figure 28-2 on page 328.
4. Tape & Reel
32.1 ATmega329
Speed (MHz)(3) Power Supply Ordering Code(2) Package Type(1) Operational Range
81.8 - 5.5V
ATmega329V-8AU
ATmega329V-8AUR(4)
ATmega329V-8MU
ATmega329V-8MUR(4)
64A
64A
64M1
64M1
Industrial
(-40°C to 85°C)
16 2.7 - 5.5V
ATmega329-16AU
ATmega329-16AUR(4)
ATmega329-16MU
ATmega329-16MUR(4)
64A
64A
64M1
64M1
Industrial
(-40°C to 85°C)
Package Type
64A 64-lead, 14 x 14 x 1.0 mm, Thin Profile Plastic Quad Flat Package (TQFP)
64M1 64-pad, 9 x 9 x 1.0 mm, Quad Flat No-Lead/Micro Lead Frame Package (QFN/MLF)
100A 100-lead, 14 x 14 x 1.0 mm, 0.5 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP)
373
2552K–AVR–04/11
ATmega329/3290/649/6490
Notes: 1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging alternative, complies to the European Directive for Restriction of Hazardous Substances (RoHS direc-
tive). Also Halide free and fully Green.
3. For Speed vs. VCC see Figure 28-1 on page 328 and Figure 28-2 on page 328.
4. Tape & Reel
32.2 ATmega3290
Speed (MHz)(3) Power Supply Ordering Code(2) Package Type(1) Operational Range
81.8 - 5.5V ATmega3290V-8AU
ATmega3290V-8AUR(4)
100A
100A
Industrial
(-40°C to 85°C)
16 2.7 - 5.5V ATmega3290-16AU
ATmega3290-16AUR(4)
100A
100A
Industrial
(-40°C to 85°C)
Package Type
64A 64-lead, 14 x 14 x 1.0 mm, Thin Profile Plastic Quad Flat Package (TQFP)
64M1 64-pad, 9 x 9 x 1.0 mm, Quad Flat No-Lead/Micro Lead Frame Package (QFN/MLF)
100A 100-lead, 14 x 14 x 1.0 mm, 0.5 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP)
374
2552K–AVR–04/11
ATmega329/3290/649/6490
Notes: 1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging alternative, complies to the European Directive for Restriction of Hazardous Substances (RoHS direc-
tive). Also Halide free and fully Green.
3. For Speed vs. VCC see Figure 28-1 on page 328 and Figure 28-2 on page 328.
4. Tape & Reel
32.3 ATmega649
Speed (MHz)(3) Power Supply Ordering Code(2) Package Type(1) Operational Range
81.8 - 5.5V
ATmega649V-8AU
ATmega649V-8AUR(4)
ATmega649V-8MU
ATmega649V-8MUR(4)
64A
64A
64M1
64M1
Industrial
(-40°C to 85°C)
16 2.7 - 5.5V
ATmega649-16AU
ATmega649-16AUR(4)
ATmega649-16MU
ATmega649-16MUR(4)
64A
64A
64M1
64M1
Industrial
(-40°C to 85°C)
Package Type
64A 64-lead, 14 x 14 x 1.0 mm, Thin Profile Plastic Quad Flat Package (TQFP)
64M1 64-pad, 9 x 9 x 1.0 mm, Quad Flat No-Lead/Micro Lead Frame Package (QFN/MLF)
100A 100-lead, 14 x 14 x 1.0 mm, 0.5 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP)
375
2552K–AVR–04/11
ATmega329/3290/649/6490
Notes: 1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging alternative, complies to the European Directive for Restriction of Hazardous Substances (RoHS direc-
tive). Also Halide free and fully Green.
3. For Speed Grades see Figure 28-1 on page 328 and Figure 28-2 on page 328.
4. Tape & Reel
32.4 ATmega6490
Speed (MHz)(3) Power Supply Ordering Code(2) Package Type(1) Operational Range
81.8 - 5.5V ATmega6490V-8AU
ATmega6490V-8AUR(4)
100A
100A
Industrial
(-40°C to 85°C)
16 2.7 - 5.5V ATmega6490-16AU
ATmega6490-16AUR(4)
100A
100A
Industrial
(-40°C to 85°C)
Package Type
64A 64-lead, 14 x 14 x 1.0 mm, Thin Profile Plastic Quad Flat Package (TQFP)
64M1 64-pad, 9 x 9 x 1.0 mm, Quad Flat No-Lead/Micro Lead Frame Package (QFN/MLF)
100A 100-lead, 14 x 14 x 1.0 mm, 0.5 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP)
376
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ATmega329/3290/649/6490
33. Packaging Information
33.1 64A
2325 Orchard Parkway
San Jose, CA 95131
TITLE DRAWING NO.
R
REV.
64A, 64-lead, 14 x 14 mm Body Size, 1.0 mm Body Thickness,
0.8 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP) C
64A
2010-10-20
PIN 1 IDENTIFIER
0°~7°
PIN 1
L
C
A1 A2 A
D1
D
e
E1 E
B
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE
Notes:
1.This package conforms to JEDEC reference MS-026, Variation AEB.
2. Dimensions D1 and E1 do not include mold protrusion. Allowable
protrusion is 0.25 mm per side. Dimensions D1 and E1 are maximum
plastic body size dimensions including mold mismatch.
3. Lead coplanarity is 0.10 mm maximum.
A – – 1.20
A1 0.05 – 0.15
A2 0.95 1.00 1.05
D 15.75 16.00 16.25
D1 13.90 14.00 14.10 Note 2
E 15.75 16.00 16.25
E1 13.90 14.00 14.10 Note 2
B 0.30 – 0.45
C 0.09 – 0.20
L 0.45 – 0.75
e 0.80 TYP
377
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33.2 64M1
2325 Orchard Parkway
San Jose, CA 95131
TITLE DRAWING NO.
R
REV.
64M1, 64-pad, 9 x 9 x 1.0 mm Body, Lead Pitch 0.50 mm,
H
64M1
2010-10-19
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE
A 0.80 0.90 1.00
A1 – 0.02 0.05
b 0.180.25 0.30
D
D2 5.20 5.40 5.60
8.909.00 9.10
8.909.00 9.10
E
E2 5.20 5.40 5.60
e 0.50 BSC
L0.35 0.40 0.45
Notes:
1. JEDEC Standard MO-220, (SAW Singulation) Fig. 1, VMMD.
2. Dimension and tolerance conform to ASMEY14.5M-1994.
TOP VIEW
SIDE VIEW
BOTTOM VIEW
D
E
Marked Pin# 1 ID
SEATING PLANE
A1
C
A
C
0.08
1
2
3
K 1.25 1.40 1.55
E2
D2
be
Pin #1 Corner
L
Pin #1
Tr i angle
Pin #1
Chamfer
(C 0.30)
Option A
Option B
Pin #1
Notch
(0.20 R)
Option C
K
K
5.40 mm Exposed Pad, Micro Lead Frame Package (MLF)
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33.3 100A
2325 Orchard Parkway
San Jose, CA 95131
TITLE DRAWING NO.
R
REV.
100A, 100-lead, 14 x 14 mm Body Size, 1.0 mm Body Thickness,
0.5 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP) D
100A
2010-10-20
PIN 1 IDENTIFIER
0°~7°
PIN 1
L
C
A1 A2 A
D1
D
eE1 E
B
A – – 1.20
A1 0.05 – 0.15
A2 0.95 1.00 1.05
D 15.75 16.00 16.25
D1 13.90 14.00 14.10 Note 2
E 15.75 16.00 16.25
E1 13.90 14.00 14.10 Note 2
B 0.17 – 0.27
C 0.09 – 0.20
L 0.45 – 0.75
e 0.50 TYP
Notes:
1. This package conforms to JEDEC reference MS-026, Variation AED.
2. Dimensions D1 and E1 do not include mold protrusion. Allowable
protrusion is 0.25 mm per side. Dimensions D1 and E1 are maximum
plastic body size dimensions including mold mismatch.
3. Lead coplanarity is 0.08 mm maximum.
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE
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34. Errata
34.1 ATmega329
34.1.1 ATmega329 rev. C
•Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem Fix/Wortkaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).
34.1.2 ATmega329 rev. B
Not sampled.
34.1.3 ATmega329 rev. A
•LCD contrast voltage too high
•Interrupts may be lost when writing the timer registers in the asynchronous timer
1. LCD contrast voltage too high
When the LCD is active and using low power waveform, the LCD contrast voltage can be too
high. This occurs when VCC is higher than VLCD, and when using low LCD drivetime.
Problem Fix/Workaround
There are several possible workarounds:
- Use normal waveform instead of low power waveform
- Use drivetime of 375 µs or longer
2. Interrupts may be lost when writing the timer registers in the asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem Fix/Wortkaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).
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34.2 ATmega3290
34.2.1 ATmega3290 rev. C
•Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem Fix/Wortkaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).
34.2.2 ATmega3290 rev. B
Not sampled.
34.2.3 ATmega3290 rev. A
•LCD contrast voltage too high
•Interrupts may be lost when writing the timer registers in the asynchronous timer
1. LCD contrast voltage too high
When the LCD is active and using low power waveform, the LCD contrast voltage can be too
high. This occurs when VCC is higher than VLCD, and when using low LCD drivetime.
Problem Fix/Workaround
There are several possible workarounds:
- Use normal waveform instead of low power waveform
- Use drivetime of 375 µs or longer
2. Interrupts may be lost when writing the timer registers in the asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem Fix/Wortkaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).
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34.3 ATmega649
34.3.1 ATmega649 rev. A
•Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem Fix/Wortkaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).
34.4 ATmega6490
34.4.1 ATmega6490 rev. A
•Interrupts may be lost when writing the timer registers in the asynchronous timer
1. Interrupts may be lost when writing the timer registers in the asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem Fix/Wortkaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).
382
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35. Datasheet Revision History
Please note that the referring page numbers in this section are referring to this document.The
referring revision in this section are referring to the document revision.
35.1 Rev. 2552K – 04/11
35.2 Rev. 2552J – 08/07
35.3 Rev. 2552I – 04/07
35.4 Rev. 2552H – 11/06
1. Removed “Preliminary” from the front page.
2. Removed “Disclaimer Section” from the datasheet.
3. Updated Table 28-5 on page 330 “BODLEVEL Fuse Coding(1)” .
4. Updated Table 28-8 on page 334 “LCD Controller Characteristics” .
5. Updated “Ordering Information” on page 372 to include “Tape & Reel” devices.
The “AI” and “MI” devices removed.
6. Updated “Errata” on page 379.
7. Updated the datasheet according to the Atmel new brand style guide, including
the last page.
1. Updated “Features” on page 1.
2. Added “Data Retention” on page 9.
3. Updated “Serial Programming Algorithm” on page 309.
4. Updated “Speed Grades” on page 328.
5. Updated “System and Reset Characteristics” on page 330.
6. Moved Register Descriptions to the end of each chapter.
1. Updated date in backpage
2. Updated column in Table 28-5 on page 330.
1. Updated Table 28-7 on page 333.
2. Updated note in Table 28-7 on page 333 and Table 28-2 on page 329.
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35.5 Rev. 2552G – 07/06
35.6 Rev. 2552F – 06/06
35.7 Rev. 2552E – 04/06
35.8 Rev. 2552D – 03/06
35.9 Rev. 2552C – 03/06
1. Updated Table 14-2 on page 104, Table 14-4 on page 104, Table 16-3 on
page 133, Table 16-5 on page 134, Table 16-5 on page 134, Table 17-2 on
page 153 and Table 17-4 on page 154.
2. Updated “Fast PWM Mode” on page 124.
3. Updated Features in “USI – Universal Serial Interface” on page 195.
4. Added “Clock speed considerations.” on page 202.
5. “Errata” on page 379.
1. Updated “Calibrated Internal RC Oscillator” on page 29.
2. Updated “OSCCAL – Oscillator Calibration Register” on page 32
3. Added Table 28-2 on page 329.
1. Updated “Calibrated Internal RC Oscillator” on page 29.
1. Updated “Errata” on page 379.
1. Added “Resources” on page 9.
2. Added Addresses in Registers.
3. Updated number of General Purpose I/O pins.
4. Updated code example in “Bit 0 – IVCE: Interrupt Vector Change Enable”
on page 53.
5. Updated Introduction in “I/O-Ports” on page 59.
6. Updated “SPI – Serial Peripheral Interface” on page 158.
7. Updated “Bit 6 – ACBG: Analog Comparator Bandgap Select” on page
209.
8. Updated Features in “Analog to Digital Converter” on page 211.
9. Updated “Prescaling and Conversion Timing” on page 214.
10. Updated features in “LCD Controller” on page 228.
11. Updated “ATmega329/3290/649/6490 Boot Loader Parameters” on page
290.
12. Updated “DC Characteristics” on page 310.
13. Updated “” on page 334.
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35.10 Rev. 2552B – 05/05
35.11 Rev. 2552A –11/04
1. MLF-package alternative changed to “Quad Flat No-Lead/Micro Lead
Frame Package QFN/MLF”.
2. Added “Pin Change Interrupt Timing” on page 54.
3. Updated Table 23-6 on page 242, Table 23-7 on page 243 and Table 27-15
on page 310.
4. Added Figure 27-12 on page 312.
5. Updated Figure 22-9 on page 219 and Figure 27-5 on page 304.
6. Updated algorithm “Enter Programming Mode” on page 299.
7. Added “Supply Current of I/O modules” on page 340.
8. Updated “Ordering Information” on page 372.
1. Initial version.
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Table of Contents
Features ..................................................................................................... 1
1 Pin Configurations ................................................................................... 2
2 Overview ................................................................................................... 4
2.1 Block Diagram ...................................................................................................4
2.2 Comparison between ATmega329, ATmega3290, ATmega649 and
ATmega6490 6
2.3 Pin Descriptions .................................................................................................6
3 Resources ................................................................................................. 9
4 Data Retention .......................................................................................... 9
5 About Code Examples ............................................................................. 9
6 AVR CPU Core ........................................................................................ 10
6.1 Overview ..........................................................................................................10
6.2 Architectural Overview .....................................................................................10
6.3 ALU – Arithmetic Logic Unit .............................................................................11
6.4 AVR Status Register ........................................................................................12
6.5 General Purpose Register File ........................................................................13
6.6 Stack Pointer ...................................................................................................14
6.7 Instruction Execution Timing ...........................................................................15
6.8Reset and Interrupt Handling ...........................................................................15
7 AVR ATmega329/3290/649/6490 Memories ......................................... 18
7.1 In-System Reprogrammable Flash Program Memory .....................................18
7.2 SRAM Data Memory ........................................................................................19
7.3 EEPROM Data Memory ..................................................................................20
7.4 I/O Memory ......................................................................................................21
7.5 Register Description ........................................................................................22
8 System Clock and Clock Options ......................................................... 26
8.1 Clock Systems and their Distribution ...............................................................26
8.2 Clock Sources .................................................................................................27
8.3 Crystal Oscillator .............................................................................................28
8.4 Low-frequency Crystal Oscillator .....................................................................29
8.5 Calibrated Internal RC Oscillator .....................................................................29
8.6 External Clock .................................................................................................31
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8.7 Clock Output Buffer .........................................................................................31
8.8Timer/Counter Oscillator ..................................................................................32
8.9 System Clock Prescaler ..................................................................................32
8.10 Register Description ........................................................................................32
9 Power Management and Sleep Modes ................................................. 35
9.1 Idle Mode .........................................................................................................36
9.2 ADC Noise Reduction Mode ............................................................................36
9.3 Power-down Mode ...........................................................................................36
9.4 Power-save Mode ............................................................................................36
9.5 Standby Mode .................................................................................................37
9.6 Power Reduction Register ...............................................................................37
9.7 Minimizing Power Consumption ......................................................................37
9.8Register Description ........................................................................................39
10 System Control and Reset .................................................................... 41
10.1 Resetting the AVR ...........................................................................................41
10.2 Reset Sources .................................................................................................41
10.3 Power-on Reset ...............................................................................................42
10.4 External Reset .................................................................................................43
10.5 Brown-out Detection ........................................................................................43
10.6 Watchdog Reset ..............................................................................................44
10.7 Internal Voltage Reference ..............................................................................44
10.8Watchdog Timer ..............................................................................................45
10.9 Timed Sequences for Changing the Configuration of the Watchdog Timer ....47
10.10 Register Description ........................................................................................47
11 Interrupts ................................................................................................ 49
11.1 Interrupt Vectors in ATmega329/3290/649/6490 .............................................49
11.2 Register Description ........................................................................................52
12 External Interrupts ................................................................................. 54
12.1 Pin Change Interrupt Timing ............................................................................54
12.2 Register Description ........................................................................................55
13 I/O-Ports .................................................................................................. 59
13.1 Introduction ......................................................................................................59
13.2 Ports as General Digital I/O .............................................................................60
13.3 Alternate Port Functions ..................................................................................65
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13.4 Register Description ........................................................................................87
14 8-bit Timer/Counter0 with PWM ............................................................ 91
14.1 Features ..........................................................................................................91
14.2 Overview ..........................................................................................................91
14.3 Timer/Counter Clock Sources .........................................................................92
14.4 Counter Unit ....................................................................................................93
14.5 Output Compare Unit .......................................................................................93
14.6 Compare Match Output Unit ............................................................................95
14.7 Modes of Operation .........................................................................................97
14.8Timer/Counter Timing Diagrams ...................................................................101
14.9 Register Description ......................................................................................103
15 Timer/Counter0 and Timer/Counter1 Prescalers .............................. 107
15.1 Register Description ......................................................................................108
16 16-bit Timer/Counter1 .......................................................................... 110
16.1 Features ........................................................................................................110
16.2 Overview ........................................................................................................110
16.3 Accessing 16-bit Registers ............................................................................113
16.4 Timer/Counter Clock Sources .......................................................................116
16.5 Counter Unit ..................................................................................................116
16.6 Input Capture Unit .........................................................................................117
16.7 Output Compare Units ...................................................................................119
16.8Compare Match Output Unit ..........................................................................122
16.9 Modes of Operation .......................................................................................123
16.10 Timer/Counter Timing Diagrams ...................................................................130
16.11 Register Description ......................................................................................132
17 8-bit Timer/Counter2 with PWM and Asynchronous Operation ...... 139
17.1 Features ........................................................................................................139
17.2 Overview ........................................................................................................139
17.3 Timer/Counter Clock Sources .......................................................................140
17.4 Counter Unit ..................................................................................................140
17.5 Output Compare Unit .....................................................................................141
17.6 Compare Match Output Unit ..........................................................................144
17.7 Modes of Operation .......................................................................................145
17.8Timer/Counter Timing Diagrams ...................................................................149
17.9 Asynchronous Operation of Timer/Counter2 .................................................151
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17.10 Timer/Counter Prescaler ...............................................................................152
17.11 Register Description ......................................................................................153
18 SPI – Serial Peripheral Interface ......................................................... 158
18.1 Features ........................................................................................................158
18.2 Overview ........................................................................................................158
18.3 SS Pin Functionality ......................................................................................163
18.4 Data Modes ...................................................................................................164
18.5 Register Description ......................................................................................165
19 USART0 ................................................................................................. 168
19.1 Features ........................................................................................................168
19.2 Overview ........................................................................................................168
19.3 Clock Generation ...........................................................................................169
19.4 Frame Formats ..............................................................................................172
19.5 USART Initialization .......................................................................................173
19.6 Data Transmission – The USART Transmitter ..............................................175
19.7 Data Reception – The USART Receiver .......................................................177
19.8Asynchronous Data Reception ......................................................................181
19.9 Multi-processor Communication Mode ..........................................................185
19.10 Examples of Baud Rate Setting .....................................................................186
19.11 Register Description ......................................................................................190
20 USI – Universal Serial Interface .......................................................... 195
20.1 Features ........................................................................................................195
20.2 Overview ........................................................................................................195
20.3 Functional Descriptions .................................................................................196
20.4 Alternative USI Usage ...................................................................................202
20.5 Register Descriptions ....................................................................................203
21 Analog Comparator ............................................................................. 207
21.1 Overview ........................................................................................................207
21.2 Analog Comparator Multiplexed Input ...........................................................208
21.3 Register Description ......................................................................................209
22 Analog to Digital Converter ................................................................ 211
22.1 Features ........................................................................................................211
22.2 Operation .......................................................................................................212
22.3 Starting a Conversion ....................................................................................213
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22.4 Prescaling and Conversion Timing ................................................................214
22.5 Changing Channel or Reference Selection ...................................................216
22.6 ADC Conversion Result .................................................................................221
22.7 Register Description ......................................................................................223
23 LCD Controller ..................................................................................... 228
23.1 Features ........................................................................................................228
23.2 Mode of Operation .........................................................................................231
23.3 LCD Usage ....................................................................................................235
23.4 Register Description ......................................................................................239
24 JTAG Interface and On-chip Debug System ..................................... 245
24.1 Features ........................................................................................................245
24.2 Overview ........................................................................................................245
24.3 Test Access Port – TAP ................................................................................245
24.4 TAP Controller ...............................................................................................247
24.5 Using the Boundary-scan Chain ....................................................................248
24.6 Using the On-chip Debug System .................................................................248
24.7 On-chip Debug Specific JTAG Instructions ...................................................249
24.8Using the JTAG Programming Capabilities ...................................................250
24.9 Bibliography ...................................................................................................250
24.10 Register Description ......................................................................................250
25 IEEE 1149.1 (JTAG) Boundary-scan ................................................... 251
25.1 Features ........................................................................................................251
25.2 System Overview ...........................................................................................251
25.3 Data Registers ...............................................................................................251
25.4 Boundary-scan Specific JTAG Instructions ...................................................253
25.5 Boundary-scan Related Register in I/O Memory ...........................................254
25.6 Boundary-scan Chain ....................................................................................255
25.7 ATmega329/3290/649/6490 Boundary-scan Order .......................................264
25.8Boundary-scan Description Language Files ..................................................277
26 Boot Loader Support – Read-While-Write Self-Programming ......... 278
26.1 Features ........................................................................................................278
26.2 Application and Boot Loader Flash Sections .................................................278
26.3 Read-While-Write and No Read-While-Write Flash Sections ........................278
26.4 Boot Loader Lock Bits ...................................................................................281
26.5 Entering the Boot Loader Program ................................................................282
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26.6 Addressing the Flash During Self-Programming ...........................................283
26.7 Self-Programming the Flash ..........................................................................283
26.8Register Description ......................................................................................291
27 Memory Programming ......................................................................... 293
27.1 Program And Data Memory Lock Bits ...........................................................293
27.2 Fuse Bits ........................................................................................................294
27.3 Signature Bytes .............................................................................................296
27.4 Calibration Byte .............................................................................................296
27.5 Parallel Programming Parameters, Pin Mapping, and Commands ...............296
27.6 Parallel Programming ....................................................................................299
27.7 Serial Downloading ........................................................................................308
27.8Programming via the JTAG Interface ............................................................313
28 Electrical Characteristics .................................................................... 326
28.1 Absolute Maximum Ratings* .........................................................................326
28.2 DC Characteristics .........................................................................................326
28.3 Speed Grades ...............................................................................................328
28.4 Clock Characteristics .....................................................................................329
28.5 System and Reset Characteristics ................................................................330
28.6 SPI Timing Characteristics ............................................................................331
28.7 ADC Characteristics ......................................................................................333
28.8LCD Controller Characteristics ......................................................................334
29 Typical Characteristics ........................................................................ 335
30 Register Summary ............................................................................... 365
31 Instruction Set Summary .................................................................... 369
32 Ordering Information ........................................................................... 372
32.1 ATmega329 ...................................................................................................372
32.2 ATmega3290 .................................................................................................373
32.3 ATmega649 ...................................................................................................374
32.4 ATmega6490 .................................................................................................375
33 Packaging Information ........................................................................ 376
33.1 64A ................................................................................................................376
33.2 64M1 ..............................................................................................................377
33.3 100A ..............................................................................................................378
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34 Errata ..................................................................................................... 379
34.1 ATmega329 ...................................................................................................379
34.2 ATmega3290 .................................................................................................380
34.3 ATmega649 ...................................................................................................381
34.4 ATmega6490 .................................................................................................381
35 Datasheet Revision History ................................................................ 382
35.1 Rev. 2552K – 04/11 .......................................................................................382
35.2 Rev. 2552J – 08/07 .......................................................................................382
35.3 Rev. 2552I – 04/07 ........................................................................................382
35.4 Rev. 2552H – 11/06 .......................................................................................382
35.5 Rev. 2552G – 07/06 ......................................................................................383
35.6 Rev. 2552F – 06/06 .......................................................................................383
35.7 Rev. 2552E – 04/06 .......................................................................................383
35.8Rev. 2552D – 03/06 .......................................................................................383
35.9 Rev. 2552C – 03/06 .......................................................................................383
35.10 Rev. 2552B – 05/05 .......................................................................................384
35.11 Rev. 2552A –11/04 ........................................................................................384
Table of Contents....................................................................................... i
2552K–AVR–04/11
Atmel Corporation
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Tel: (+1)(408) 441-0311
Fax: (+1)(408) 487-2600
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