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Farnell PDF
ATmega329/3290/649/6490 Datasheet - Farnell Element 14
ATmega329/3290/649/6490 Datasheet - Farnell Element 14
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Farnell Element 14 :
See the trailer for the next exciting episode of The Ben Heck show. Check back on Friday to be among the first to see the exclusive full show on element…
Connect your Raspberry Pi to a breadboard, download some code and create a push-button audio play project.
Puce électronique / Microchip :
Sans fil - Wireless :
Texas instrument :
Ordinateurs :
Logiciels :
Tutoriels :
Autres documentations :
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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–04/112
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
TQFP3
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 connected
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
A
GND
AREF
PF0 (ADC0)
PF1 (ADC1)
PF2 (ADC2)
PF3 (ADC3)
PF4 (ADC4/TCK)
PF5 (ADC5/TMS)
PF6 (ADC6/TDO)
PF7 (ADC7/TDI)
GND
VCC 17
61
60
18
59
20
58
19
21
57
22
56
23
55
24
54
25
53
26
52
27
51
28
29
50
49
30
31
32
(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)
(SEG19) PD3
(SEG18) PD4
(SEG17) PD5
(SEG16) PD6
(SEG20) PD2
(ICP1/SEG22) PD0
(INT0/SEG21) PD1
(TOSC2) XTAL2
(TOSC1) XTAL1
RESET/PG5
V
GND
CC
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
ATmega329/6494
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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 architecture.
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
USART SPI
STATUS
REGISTER
Z
Y
X
ALU
PORTE DRIVERS PORTB DRIVERS
PORTF DRIVERS PORTA DRIVERS
PORTD DRIVERS
PORTC DRIVERS
PE0 - PE7 PB0 - PB7
PF0 - PF7 PA0 - PA7 GND VCC
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
BOUNDARYSCAN
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
PORTJ5
2552K–AVR–04/11
ATmega329/3290/649/6490
The Atmel® AVR® core combines a rich instruction set with 32 general purpose working registers.
All the 32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two
independent registers to be accessed in one single instruction executed in one clock cycle. The
resulting architecture is more code efficient while achieving throughputs up to ten times faster
than conventional CISC microcontrollers.
The Atmel ATmega329/3290/649/6490 provides the following features: 32/64K bytes of In-System
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, internal
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 continue
functioning. The Power-down mode saves the register contents but freezes the Oscillator,
disabling all other chip functions until the next interrupt or hardware reset. In Power-save mode,
the asynchronous timer 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 crystal/resonator
Oscillator is running while the rest of the device is sleeping. This allows very fast
start-up combined with low-power consumption.
The device is manufactured using Atmel’s high density non-volatile memory technology. The
On-chip In-System re-Programmable (ISP) Flash allows the program memory to be reprogrammed
In-System through an SPI serial interface, by a conventional non-volatile memory
programmer, or by an On-chip Boot program running on the AVR core. The Boot program can
use any interface to download the application program in the Application Flash memory. Software
in the Boot Flash section will continue to run while the Application Flash section is updated,
providing true Read-While-Write operation. By combining an 8-bit RISC CPU with In-System
Self-Programmable Flash on a monolithic chip, the Atmel ATmega329/3290/649/6490 is a powerful
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.6
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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 40 697
2552K–AVR–04/11
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 symmetrical
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.8
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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 capability.
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 connected
to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC
through a low-pass filter.
2.3.16 AREF
This is the analog reference pin for the A/D Converter.9
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 Figure
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 documentation
for more details.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.10
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 instruction
is pre-fetched from the program memory. This concept enables instructions to be executed
in every clock cycle. The program memory is In-System Reprogrammable Flash memory.
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 n11
2552K–AVR–04/11
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 typical
ALU operation, two operands are output from the Register File, the operation is executed,
and the result is stored back in the Register File – in one clock cycle.
Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data
Space addressing – enabling efficient address calculations. One of the these address pointers
can also be used as an address pointer for look up tables in Flash program memory. These
added function registers are the 16-bit X-, Y-, and Z-register, described later in this section.
The ALU supports arithmetic and logic operations between registers or between a constant and
a register. Single register operations can also be executed in the ALU. After an arithmetic operation,
the Status Register is updated to reflect information about the result of the operation.
Program flow is provided by conditional and unconditional jump and call instructions, able to
directly address the whole address space. Most AVR instructions have a single 16-bit word format.
Every program memory address contains a 16- or 32-bit instruction.
Program Flash memory space is divided in two sections, the Boot Program section and the
Application Program section. Both sections have dedicated Lock bits for write and read/write
protection. The SPM instruction that writes into the Application Flash memory section must
reside in the Boot Program section.
During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the
Stack. The Stack is effectively allocated in the general data SRAM, and consequently the Stack
size is only limited by the total SRAM size and the usage of the SRAM. All user programs must
initialize the SP in the Reset routine (before subroutines or interrupts are executed). The Stack
Pointer (SP) is read/write accessible in the I/O space. The data SRAM can easily be accessed
through the five different addressing modes supported in the AVR architecture.
The memory spaces in the AVR architecture are all linear and regular memory maps.
A flexible interrupt module has its control registers in the I/O space with an additional Global
Interrupt Enable bit in the Status Register. All interrupts have a separate Interrupt Vector in the
Interrupt Vector table. The interrupts have priority in accordance with their Interrupt Vector position.
The lower the Interrupt Vector address, the higher the priority.
The I/O memory space contains 64 addresses for CPU peripheral functions as Control Registers,
SPI, and other I/O functions. The I/O Memory can be accessed directly, or as the Data
Space locations following those of the Register File, 0x20 - 0x5F. In addition, the
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.12
2552K–AVR–04/11
ATmega329/3290/649/6490
6.4 AVR Status Register
The Status Register contains information about the result of the most recently executed arithmetic
instruction. This information can be used for altering program flow in order to perform
conditional operations. Note that the Status Register is updated after all ALU operations, as
specified in the Instruction Set Reference. This will in many cases remove the need for using the
dedicated compare instructions, resulting in faster and more compact code.
The Status Register is not automatically stored when entering an interrupt routine and restored
when returning from an interrupt. This must be handled by software.
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 interrupt
enable control is then performed in separate control registers. If the Global Interrupt Enable
Register is cleared, none of the interrupts are enabled independent of the individual interrupt
enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is set by
the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared by
the application with the SEI and CLI instructions, as described in the instruction set reference.
• Bit 6 – T: Bit Copy Storage
The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or destination
for the operated bit. A bit from a register in the Register File can be copied into T by the
BST instruction, and a bit in T can be copied into a bit in a register in the Register File by the
BLD instruction.
• Bit 5 – H: Half Carry Flag
The Half Carry Flag H indicates a Half Carry in some arithmetic operations. Half Carry Is useful
in BCD arithmetic. See the “Instruction Set Description” for detailed information.
• Bit 4 – S: Sign Bit, S = N ⊕ V
The S-bit is always an exclusive or between the Negative Flag N and the Two’s Complement
Overflow Flag V. See the “Instruction Set Description” for detailed information.
• Bit 3 – V: Two’s Complement Overflow Flag
The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See the
“Instruction Set Description” for detailed information.
• Bit 2 – N: Negative Flag
The Negative Flag N indicates a negative result in an arithmetic or logic operation. See the
“Instruction Set Description” for detailed information.
• Bit 1 – Z: Zero Flag
The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction
Set Description” for detailed information.
Bit 7 6 5 4 3 2 1 0
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 0 013
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ATmega329/3290/649/6490
• 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 implemented
as SRAM locations, this memory organization provides great flexibility in access of the
registers, as the X-, Y- and Z-pointer registers can be set to index any register in the file.
7 0 Addr.
R0 0x00
R1 0x01
R2 0x02
…
R13 0x0D
General R14 0x0E
Purpose R15 0x0F
Working R16 0x10
Registers R17 0x11
…
R26 0x1A X-register Low Byte
R27 0x1B X-register High Byte
R28 0x1C Y-register Low Byte
R29 0x1D Y-register High Byte
R30 0x1E Z-register Low Byte
R31 0x1F Z-register High Byte14
2552K–AVR–04/11
ATmega329/3290/649/6490
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 registers
are 16-bit address pointers for indirect addressing of the data space. The three indirect
address registers X, Y, and Z are defined as described in Figure 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 locations
to lower memory locations. This implies that a Stack PUSH command decreases the Stack
Pointer.
The Stack Pointer points to the data SRAM Stack area where the Subroutine and Interrupt
Stacks are located. This Stack space in the data SRAM must be defined by the program before
any subroutine calls are executed or interrupts are enabled. The Stack Pointer must be set to
point above 0x60. The Stack Pointer is decremented by one when data is pushed onto the Stack
with the PUSH instruction, and it is decremented by two when the return address is pushed onto
the Stack with subroutine call or interrupt. The Stack Pointer is incremented by one when data is
popped from the Stack with the POP instruction, and it is incremented by two when data is
popped from the Stack with return from subroutine RET or return from interrupt RETI.
The AVR Stack Pointer is implemented as two 8-bit registers in the I/O space. The number of
bits actually used is implementation dependent. Note that the data space in some implementations
of the AVR architecture is so small that only SPL is needed. In this case, the SPH Register
will not be present.
15 XH XL 0
X-register 7 07 0
R27 (0x1B) R26 (0x1A)
15 YH YL 0
Y-register 7 07 0
R29 (0x1D) R28 (0x1C)
15 ZH ZL 0
Z-register 70 7 0
R31 (0x1F) R30 (0x1E)
Bit 15 14 13 12 11 10 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
0000000015
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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 Harvard
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 destination
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 Programming”
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
clkCPU16
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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 disabled.
The user software can write logic one to the I-bit to enable nested interrupts. All enabled
interrupts can then interrupt the current interrupt routine. The I-bit is automatically set when a
Return from Interrupt instruction – RETI – is executed.
There are basically two types of interrupts. The first type is triggered by an event that sets the
Interrupt Flag. For these interrupts, the Program Counter is vectored to the actual Interrupt Vector
in order to execute the interrupt handling routine, and hardware clears the corresponding
Interrupt Flag. Interrupt Flags can also be cleared by writing a logic one to the flag bit position(s)
to be cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is
cleared, the Interrupt Flag will be set and remembered until the interrupt is enabled, or the flag is
cleared by software. Similarly, if one or more interrupt conditions occur while the Global Interrupt
Enable bit is cleared, the corresponding Interrupt Flag(s) will be set and remembered until the
Global Interrupt Enable bit is set, and will then be executed by order of priority.
The second type of interrupts will trigger as long as the interrupt condition is present. These
interrupts do not necessarily have Interrupt Flags. If the interrupt condition disappears before the
interrupt is enabled, the interrupt will not be triggered.
When the AVR exits from an interrupt, it will always return to the main program and execute one
more instruction before any pending interrupt is served.
Note that the Status Register is not automatically stored when entering an interrupt routine, nor
restored when returning from an interrupt routine. This must be handled by software.
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< 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
xxx
... ... ...52
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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 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 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 determined
by the BOOTSZ Fuses. Refer to the section “Boot Loader Support – Read-While-Write
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 0 053
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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-WhileWrite
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< CSn2:0 > 1). The number of system clock
cycles from when the timer is enabled to the first count occurs can be from 1 to N+1 system
clock cycles, where N equals the prescaler divisor (8, 64, 256, or 1024).
It is possible to use the prescaler reset for synchronizing the Timer/Counter to program execution.
However, care must be taken if the other Timer/Counter that shares the same prescaler
also uses prescaling. A prescaler reset will affect the prescaler period for all Timer/Counters it is
connected to.
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)
Synchronization Edge Detector
D Q D Q
LE
Tn D Q
clkI/O108
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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 system
clock frequency (fExtClk < fclk_I/O/2) given a 50/50% duty cycle. Since the edge detector uses
sampling, the maximum frequency of an external clock it can detect is half the sampling frequency
(Nyquist sampling theorem). However, due to variation of the system clock frequency
and duty cycle caused by Oscillator source (crystal, resonator, and capacitors) tolerances, it is
recommended that maximum frequency of an external clock source is less than fclk_I/O/2.5.
An external clock source can not be prescaled.
Figure 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 prescaler
reset signals asserted. This ensures that the corresponding Timer/Counters are halted and
can be configured to the same value without the risk of one of them advancing during configuration.
When the TSM bit is written to zero, the 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
clkT1 clkT0
T1
T0
clkI/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 0109
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When this bit is one, Timer/Counter1 and Timer/Counter0 prescaler will be Reset. This bit is normally
cleared immediately by hardware, except if the TSM bit is set. Note that Timer/Counter1
and Timer/Counter0 share the same prescaler and a reset of this prescaler will affect both
timers.110
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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 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 132.
The PRTIM1 bit in “Power Reduction Register” on page 37 must be written to zero to enable the
Timer/Counter1 module.111
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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 Register
(ICR1) are all 16-bit registers. Special procedures must be followed when accessing the 16-
bit registers. These procedures are described in the section “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/Counter
value at all time. The result of the compare can be used by the Waveform Generator to
generate a PWM or variable frequency output on the Output Compare pin (OC1A/B). See “OutClock
Select
Timer/Counter
DATA BUS
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 )
clkTn112
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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 triggered)
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 Register.
The assignment is dependent of the mode of operation.113
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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 temporary
register in the same clock cycle as the low byte is read.
Not all 16-bit accesses uses the temporary register for the high byte. Reading the OCR1A/B 16-
bit registers does not involve using the temporary register.
To do a 16-bit write, the high byte must be written before the low byte. For a 16-bit read, the low
byte must be read before the high byte.
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 Registers,
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;
...114
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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;
}115
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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 written
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;
}116
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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).
clkT1 Timer/Counter clock.
TOP Signalize that TCNT1 has reached maximum value.
BOTTOM Signalize that TCNT1 has reached minimum value (zero).
The 16-bit counter is mapped into two 8-bit I/O memory locations: Counter High (TCNT1H) containing
the upper eight bits of the counter, and Counter Low (TCNT1L) containing the lower eight
bits. The TCNT1H Register can only be indirectly accessed by the CPU. When the CPU does an
access to the TCNT1H I/O location, the CPU accesses the high byte temporary register (TEMP).
The temporary register is updated with the TCNT1H value when the TCNT1L is read, and
TCNT1H is updated with the temporary register value when TCNT1L is written. This allows the
CPU to read or write the entire 16-bit counter value within one clock cycle via the 8-bit data bus.
It is important to notice that there are special cases of writing to the TCNT1 Register when the
counter is counting that will give unpredictable results. The special cases are described in the
sections where they are of importance.
Depending on the mode of operation used, the counter is cleared, incremented, or decremented
at each timer clock (clkT1). The clkT1 can be generated from an external or internal clock source,
selected by the Clock Select bits (CS12:0). When no clock source is selected (CS12:0 = 0) the
timer is stopped. However, the TCNT1 value can be accessed by the CPU, independent of
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 )
clkTn117
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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 multiple
events, can be applied via the ICP1 pin or alternatively, via the analog-comparator unit. The
time-stamps can then be used to calculate frequency, duty-cycle, and other features of the signal
applied. Alternatively the time-stamps can be used for creating a log of the events.
The Input Capture unit is illustrated by the block diagram shown in Figure 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)
ACO* ACIC* ICNC ICES118
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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 Generation
mode (WGM13:0) bits must be set before the TOP value can be written to the ICR1
Register. When writing the ICR1 Register the high byte must be written to the ICR1H I/O location
before the low byte is written to ICR1L.
For more information on how to access the 16-bit registers refer to “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 Waveform
Generation mode that uses ICR1 to define TOP.
An Input Capture can be triggered by software by controlling the port of the ICP1 pin.
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 additional
four system clock cycles of delay from a change applied to the input, to the update of the
ICR1 Register. The noise canceler uses the system clock and is therefore not affected by the
prescaler.
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 interrupt
handler routine as possible. Even though the Input Capture interrupt has relatively high119
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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 Compare
Flag generates an Output Compare interrupt. The OCF1x Flag is automatically cleared
when the interrupt is executed. Alternatively the OCF1x Flag can be cleared by software by writing
a logical one to its I/O bit location. The Waveform Generator uses the match signal to
generate an output according to operating mode set by the Waveform Generation mode
(WGM13:0) bits and Compare Output mode (COM1x1:0) bits. The TOP and BOTTOM signals
are used by the Waveform Generator for handling the special cases of the extreme values in
some modes of operation (See “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.120
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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 Compare
Register to either TOP or BOTTOM of the counting sequence. The synchronization
prevents the occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output
glitch-free.
The OCR1x Register access may seem complex, but this is not case. When the double buffering
is enabled, the CPU has access to the OCR1x Buffer Register, and if double buffering is disabled
the CPU will access the OCR1x directly. The content of the OCR1x (Buffer or Compare)
Register is only changed by a write operation (the Timer/Counter does not update this register
automatically as the TCNT1 and ICR1 Register). Therefore OCR1x is not read via the high byte
temporary register (TEMP). However, it is a good practice to read the low byte first as when
accessing other 16-bit registers. Writing the OCR1x Registers must be done via the TEMP Register
since the compare of all 16 bits is done continuously. The high byte (OCR1xH) has to be
written first. When the high byte I/O location is written by the CPU, the TEMP Register will be
updated by the value written. Then when the low byte (OCR1xL) is written to the lower eight bits,
the high byte will be copied into the upper 8-bits of either the OCR1x buffer or OCR1x Compare
Register in the same system clock cycle.
For more information of how to access the 16-bit registers refer to “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)
WGMn3:0 COMnx1:0
OCRnx (16-bit Register)
OCRnxH (8-bit) OCRnxL (8-bit)
Waveform Generator
TOP
BOTTOM121
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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 Compare
(FOC1x) strobe bits in Normal mode. The OC1x Register keeps its value even when
changing between Waveform Generation modes.
Be aware that the COM1x1:0 bits are not double buffered together with the compare value.
Changing the COM1x1:0 bits will take effect immediately.122
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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 output)
is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction
Register bit for the OC1x pin (DDR_OC1x) must be set as output before the OC1x value is visible
on the pin. The port override function is generally independent of the Waveform Generation
mode, but there are some exceptions. Refer to Table 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 output
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
D Q
D Q
OCnx
OCnx Pin
D Q Waveform
Generator
COMnx1
COMnx0
0
1
DATA BUS
FOCnx
clkI/O123
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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 output
generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes
the COM1x1:0 bits control whether the output should be set, cleared or toggle at a compare
match (See “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 software.
There are no special cases to consider in the Normal mode, a new counter value can be
written anytime.
The Input Capture unit is easy to use in Normal mode. However, observe that the maximum
interval between the external events must not exceed the resolution of the counter. If the interval
between events are too long, the timer overflow interrupt or the prescaler must be used to
extend the resolution for the capture unit.
The Output Compare units can be used to generate interrupts at some given time. Using the
Output Compare to generate waveforms in Normal mode is not recommended, since this will
occupy too much of the CPU time.
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. This124
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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 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. However,
changing the TOP to a value close to BOTTOM when the counter is running with none or a
low prescaler value must be done with care since the CTC mode does not have the double buffering
feature. If the new value written to OCR1A or ICR1 is lower than the current value of
TCNT1, the counter will miss the compare match. The counter will then have to count to its maximum
value (0xFFFF) and wrap around starting at 0x0000 before the compare match can occur.
In many cases this feature is not desirable. An alternative will then be to use the fast PWM mode
using OCR1A for defining TOP (WGM13:0 = 15) since the OCR1A then will be double buffered.
For generating a waveform output in CTC mode, the OC1A output can be set to toggle its logical
level on each compare match by setting the Compare Output mode bits to toggle mode
(COM1A1:0 = 1). The OC1A value will not be visible on the port pin unless the data direction for
the pin is set to output (DDR_OC1A = 1). The waveform generated will have a maximum frequency
of fOC1A = fclk_I/O/2 when OCR1A is set to zero (0x0000). The waveform frequency is
defined by the following equation:
The N variable represents the prescaler factor (1, 8, 64, 256, or 1024).
As for the Normal mode of operation, the TOV1 Flag is set in the same timer clock cycle that the
counter counts from MAX to 0x0000.
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)
Period 1 2 3 4
(COMnA1:0 = 1)
f
OCnA
f
clk_I/O
2 ⋅ ⋅ N ( ) 1 + OCRnA = --------------------------------------------------125
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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 correct
and phase and frequency correct PWM modes that use dual-slope operation. This high
frequency makes the fast PWM mode well suited for power regulation, rectification, and DAC
applications. High frequency allows physically small sized external components (coils, capacitors),
hence reduces total system cost.
The PWM resolution for fast PWM can be fixed to 8-, 9-, or 10-bit, or defined by either ICR1 or
OCR1A. The minimum resolution allowed is 2-bit (ICR1 or OCR1A set to 0x0003), and the maximum
resolution is 16-bit (ICR1 or OCR1A set to MAX). The PWM resolution in bits can be
calculated by using the following equation:
In fast PWM mode the counter is incremented until the counter value matches either one of the
fixed values 0x00FF, 0x01FF, or 0x03FF (WGM13:0 = 5, 6, or 7), the value in ICR1 (WGM13:0 =
14), or the value in OCR1A (WGM13:0 = 15). The counter is then cleared at the following timer
clock cycle. The timing diagram for the fast PWM mode is shown in Figure 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 handler
routine can be used for updating the TOP and compare values.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the Compare Registers. If the TOP value is lower than any of the
Compare Registers, a compare match will never occur between the TCNT1 and the OCR1x.
Note that when using fixed TOP values the unused bits are masked to zero when any of the
OCR1x Registers are written.
RFPWM
log( ) TOP + 1
log( ) 2 = -----------------------------------
TCNTn
OCRnx / TOP Update
and TOVn Interrupt Flag
Set and OCnA Interrupt
Flag Set or ICFn
Interrupt Flag Set
(Interrupt on TOP)
Period 1 2 3 4 5 6 7 8
OCnx
OCnx
(COMnx1:0 = 2)
(COMnx1:0 = 3)126
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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 output
will be a narrow spike for each TOP+1 timer clock cycle. Setting the OCR1x equal to TOP
will result in a constant high or low output (depending on the polarity of the output set by the
COM1x1:0 bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting
OC1A to toggle its logical level on each compare match (COM1A1:0 = 1). This applies only
if OCR1A is used to define the TOP value (WGM13:0 = 15). The waveform generated will have
a maximum frequency of fOC1A = fclk_I/O/2 when OCR1A is set to zero (0x0000). This feature is
similar to the OC1A toggle in CTC mode, except the double buffer feature of the Output Compare
unit is enabled in the fast PWM mode.
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 dualslope
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
f
OCnxPWM
f
clk_I/O
N ⋅ ( ) 1 + TOP = -----------------------------------127
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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 resolution
in bits can be calculated by using the following equation:
In phase correct PWM mode the counter is incremented until the counter value matches either
one of the fixed values 0x00FF, 0x01FF, or 0x03FF (WGM13:0 = 1, 2, or 3), the value in ICR1
(WGM13:0 = 10), or the value in OCR1A (WGM13:0 = 11). The counter has then reached the
TOP and changes the count direction. The TCNT1 value will be equal to TOP for one timer clock
cycle. The timing diagram for the phase correct PWM mode is shown on Figure 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 Interrupt
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 accordingly
at the same timer clock cycle as the OCR1x Registers are updated with the double buffer
value (at TOP). The Interrupt Flags can be used to generate an interrupt each time the counter
reaches the TOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the Compare Registers. If the TOP value is lower than any of the
Compare Registers, a compare match will never occur between the TCNT1 and the OCR1x.
RPCPWM
log( ) TOP + 1
log( ) 2 = -----------------------------------
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)128
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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 Register.
Since the OCR1x update occurs at TOP, the PWM period starts and ends at TOP. This
implies that the length of the falling slope is determined by the previous TOP value, while the
length of the rising slope is determined by the new TOP value. When these two values differ the
two slopes of the period will differ in length. The difference in length gives the unsymmetrical
result on the output.
It is recommended to use the phase and frequency correct mode instead of the phase correct
mode when changing the TOP value while the Timer/Counter is running. When using a static
TOP value there are practically no differences between the two modes of operation.
In phase correct PWM mode, the compare units allow generation of PWM waveforms on the
OC1x pins. Setting the COM1x1:0 bits to two will produce a non-inverted PWM and an inverted
PWM output can be generated by setting the COM1x1:0 to three (See Table 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 waveform
generation option. The phase and frequency correct PWM mode is, like the phase correct
PWM mode, based on a dual-slope operation. The counter counts repeatedly from BOTTOM
(0x0000) to TOP and then from TOP to BOTTOM. In non-inverting Compare Output mode, the
Output Compare (OC1x) is cleared on the compare match between TCNT1 and OCR1x while
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 frequency
compared to the single-slope operation. However, due to the symmetric feature of the
dual-slope PWM modes, these modes are preferred for motor control applications.
The main difference between the phase correct, and the phase and frequency correct PWM
mode is the time the OCR1x Register is updated by the OCR1x Buffer Register, (see Figure 16-
8 and Figure 16-9).
f
OCnxPCPWM
f
clk_I/O
2 ⋅ ⋅ N TOP = ----------------------------129
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ATmega329/3290/649/6490
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 diagram
shown as a histogram for illustrating the dual-slope operation. The diagram includes noninverted
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 16-9. 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, symmetrical
in all periods. Since the OCR1x Registers are updated at BOTTOM, the length of the rising
and the falling slopes will always be equal. This gives symmetrical output pulses and is therefore
frequency correct.
RPFCPWM
log( ) TOP + 1
log( ) 2 = -----------------------------------
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)130
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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 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
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 noninverted
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.
f
OCnxPFCPWM
f
clk_I/O
2 ⋅ ⋅ N TOP = ----------------------------
clkTn
(clkI/O/1)
OCFnx
clkI/O
OCRnx
TCNTn
OCRnx Value
OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2131
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ATmega329/3290/649/6490
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
clkI/O
clkTn
(clkI/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
clkTn
(clkI/O/1)
clkI/O132
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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 respectively)
behavior. If one or both of the COM1A1:0 bits are written to one, the OC1A output
overrides the normal port functionality of the I/O pin it is connected to. If one or both of the
COM1B1:0 bit are written to one, the OC1B output overrides the normal port functionality of the
I/O pin it is connected to. However, note that the Data Direction Register (DDR) bit corresponding
to the OC1A or OC1B pin must be set in order to enable the output driver.
When the OC1A or OC1B is connected to the pin, the function of the COM1x1:0 bits is dependent
of the WGM13:0 bits setting. Table 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
clkI/O
clkTn
(clkI/O/8)
Bit 7 6 5 4 3 2 1 0
(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
0 0 Normal port operation, OC1A/OC1B
disconnected.
0 1 Toggle OC1A/OC1B on Compare Match.
1 0 Clear OC1A/OC1B on Compare Match (Set
output to low level).
1 1 Set OC1A/OC1B on Compare Match (Set output
to high level).133
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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 waveform
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
0 0 Normal port operation, OC1A/OC1B
disconnected.
0 1 WGM13:0 = 14 or 15: Toggle OC1A on Compare
Match, OC1B disconnected (normal port
operation). For all other WGM1 settings, normal
port operation, OC1A/OC1B disconnected.
1 0 Clear OC1A/OC1B on Compare Match, set
OC1A/OC1B at 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
0 0 Normal 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 upcounting.
Set OC1A/OC1B on Compare Match
when counting down.
1 1 Set OC1A/OC1B on Compare Match when upcounting.
Clear OC1A/OC1B on Compare Match
when counting down.134
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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
00 0 0 0 Normal 0xFFFF Immediate MAX
1 0 0 0 1 PWM, Phase Correct, 8-bit 0x00FF TOP BOTTOM
2 0 0 1 0 PWM, Phase Correct, 9-bit 0x01FF TOP BOTTOM
3 0 0 1 1 PWM, Phase Correct, 10-bit 0x03FF TOP BOTTOM
4 0 1 0 0 CTC OCR1A Immediate MAX
5 0 1 0 1 Fast PWM, 8-bit 0x00FF BOTTOM TOP
6 0 1 1 0 Fast PWM, 9-bit 0x01FF BOTTOM TOP
7 0 1 1 1 Fast PWM, 10-bit 0x03FF BOTTOM TOP
8 1 0 0 0 PWM, Phase and Frequency
Correct
ICR1 BOTTOM BOTTOM
9 1 0 0 1 PWM, Phase and Frequency
Correct
OCR1A BOTTOM BOTTOM
10 1 0 1 0 PWM, Phase Correct ICR1 TOP BOTTOM
11 1 0 1 1 PWM, Phase Correct OCR1A TOP BOTTOM
12 1 1 0 0 CTC ICR1 Immediate MAX
13 1 1 0 1 (Reserved) – – –
14 1 1 1 0 Fast PWM ICR1 BOTTOM TOP
15 1 1 1 1 Fast PWM OCR1A BOTTOM TOP
Bit 7 6 5 4 3 2 1 0
(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 0135
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ATmega329/3290/649/6490
When the ICR1 is used as TOP value (see description of the WGM13:0 bits located in the
TCCR1A and the TCCR1B Register), the ICP1 is disconnected and consequently the Input Capture
function is disabled.
• Bit 5 – Reserved Bit
This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be
written to zero when TCCR1B is written.
• Bit 4:3 – WGM13:2: Waveform Generation Mode
See TCCR1A Register description.
• Bit 2:0 – CS12:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter, see Figure
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
000 No clock source (Timer/Counter stopped).
0 0 1 clkI/O/1 (No prescaling)
0 1 0 clkI/O/8 (From prescaler)
0 1 1 clkI/O/64 (From prescaler)
1 0 0 clkI/O/256 (From prescaler)
1 0 1 clkI/O/1024 (From prescaler)
1 1 0 External clock source on T1 pin. Clock on falling edge.
1 1 1 External clock source on T1 pin. Clock on rising edge.
Bit 7 6 5 4 3 2 1 0
(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 0136
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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 compare
match between TCNT1 and one of the OCR1x Registers.
Writing to the TCNT1 Register blocks (removes) the compare match on the following timer clock
for all compare units.
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 7 6 5 4 3 2 1 0
(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 Value 0 0 0 0 0 0 0 0
Bit 7 6 5 4 3 2 1 0
(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 Value 0 0 0 0 0 0 0 0
Bit 7 6 5 4 3 2 1 0
(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 Value 0 0 0 0 0 0 0 0137
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ATmega329/3290/649/6490
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 7 6 5 4 3 2 1 0
(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 Value 0 0 0 0 0 0 0 0
Bit 7 6 5 4 3 2 1 0
(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 0138
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ATmega329/3290/649/6490
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 counter
reaches the TOP value.
ICF1 is automatically cleared when the Input Capture Interrupt Vector is executed. Alternatively,
ICF1 can be cleared by writing a logic one to its bit location.
• Bit 2 – OCF1B: Timer/Counter1, Output Compare B Match Flag
This flag is set in the timer clock cycle after the counter (TCNT1) value matches the Output
Compare Register B (OCR1B).
Note that a Forced Output Compare (FOC1B) strobe will not set the OCF1B Flag.
OCF1B is automatically cleared when the Output Compare Match B Interrupt Vector is executed.
Alternatively, OCF1B can be cleared by writing a logic one to its bit location.
Bit 1 – OCF1A: Timer/Counter1, Output Compare A Match Flag
This flag is set in the timer clock cycle after the counter (TCNT1) value matches the Output
Compare Register A (OCR1A).
Note that a Forced Output Compare (FOC1A) strobe will not set the OCF1A Flag.
OCF1A is automatically cleared when the Output Compare Match A Interrupt Vector is executed.
Alternatively, OCF1A can be cleared by writing a logic one to its bit location.
• Bit 0 – TOV1: Timer/Counter1, Overflow Flag
The setting of this flag is dependent of the WGM13:0 bits setting. In Normal and CTC modes,
the TOV1 Flag is set when the timer overflows. Refer to Table 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 7 6 5 4 3 2 1 0
0x16 (0x36) – – ICF1 – – OCF1B OCF1A TOV1 TIFR1
Read/Write R R R/W R R R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0139
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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 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 153.
Figure 17-1. 8-bit Timer/Counter Block Diagram
Timer/Counter
DATA BUS
=
TCNTn
Waveform
Generation OCnx
= 0
Control Logic
= 0xFF
BOTTOM TOP
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/O140
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17.2.1 Registers
The Timer/Counter (TCNT2) and Output Compare Register (OCR2A) are 8-bit registers. Interrupt
request (shorten as Int.Req.) signals are all visible in the Timer Interrupt Flag Register
(TIFR2). All interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK2).
TIFR2 and TIMSK2 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or asynchronously clocked from
the TOSC1/2 pins, as detailed later in this section. The asynchronous operation is controlled by
the Asynchronous Status Register (ASSR). The Clock Select logic block controls which clock
source 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 (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 generate
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.141
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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).
clkT2 Timer/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 software
by writing a logical one to its I/O bit location. The Waveform Generator uses the match
signal to generate an output according to operating mode set by the WGM21:0 bits and Compare
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.)
bottom top
direction
clear
TOSC1
T/C
Oscillator
TOSC2
Prescaler
clkI/O
clk Tn142
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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 buffering
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 initialized
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 BUS
TCNTn
WGMn1:0
Waveform Generator
top
FOCn
COMnX1:0
bottom143
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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 Compare
(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.144
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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 simplified
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 Registers
(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 output)
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 visible
on the pin. The port override function is independent of the Waveform Generation mode.
The design of the Output Compare pin logic allows initialization of the 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
D Q
D Q
OCnx
OCnx Pin
D Q Waveform
Generator
COMnx1
COMnx0
0
1
DATA BUS
FOCnx
clkI/O145
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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 bottom
(0x00). In normal operation the Timer/Counter Overflow Flag (TOV2) will be set in the same
timer clock cycle as the TCNT2 becomes zero. The TOV2 Flag in this case behaves like a ninth
bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt
that automatically clears the TOV2 Flag, the timer resolution can be increased by software.
There are no special cases to consider in the Normal mode, a new counter value can be written
anytime.
The Output Compare unit can be used to generate interrupts at some given time. Using the Output
Compare to generate waveforms in Normal mode is not recommended, since this will
occupy too much of the CPU time.
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.146
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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 current
value of TCNT2, the counter will miss the compare match. The counter will then have to
count to its maximum value (0xFF) and wrap around starting at 0x00 before the compare match
can occur.
For generating a waveform output in CTC mode, the OC2A output can be set to toggle its logical
level on each compare match by setting the Compare Output mode bits to toggle mode
(COM2A1:0 = 1). The OC2A value will not be visible on the port pin unless the data direction for
the pin is set to output. The waveform generated will have a maximum frequency of fOC2A =
fclk_I/O/2 when OCR2A is set to zero (0x00). The waveform frequency is defined by the following
equation:
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
As for the Normal mode of operation, the TOV2 Flag is set in the same timer clock cycle that the
counter counts from MAX to 0x00.
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 single-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
Period 1 2 3 4
(COMnx1:0 = 1)
f
OCnx
f
clk_I/O
2 ⋅ ⋅ N ( ) 1 + OCRnx = -------------------------------------------------147
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PWM mode is shown in Figure 17-6. The TCNT2 value is in the timing diagram shown as a histogram
for illustrating the single-slope operation. The diagram includes non-inverted and
inverted PWM outputs. The small horizontal line marks on the TCNT2 slopes represent compare
matches between 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 interrupt
is enabled, the interrupt handler routine can be used for updating the compare value.
In fast PWM mode, the compare unit allows generation of PWM waveforms on the 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 output.
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 setting
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 feature
is similar to the OC2A toggle in CTC mode, except the double buffer feature of the Output
Compare unit is enabled in the fast PWM mode.
TCNTn
OCRnx Update and
TOVn Interrupt Flag Set
Period 1 2 3
OCnx
OCnx
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCRnx Interrupt Flag Set
4 5 6 7
f
OCnxPWM
f
clk_I/O
N ⋅ 256 = ------------------148
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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 noninverting
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 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 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 Update149
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decrements. The PWM frequency for the output when using phase correct PWM can be calculated
by the following equation:
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
The extreme values for the OCR2A Register represent special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCR2A is set equal to BOTTOM, the
output will be continuously low and if set equal to MAX the output will be continuously high for
non-inverted PWM mode. For inverted PWM the output will have the opposite logic values.
At the very start of period 2 in Figure 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 BOTTOM.
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 upcounting
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.
f
OCnxPCPWM
f
clk_I/O
N ⋅ 510 = ------------------
clkTn
(clkI/O/1)
TOVn
clkI/O
TCNTn MAX - 1 MAX BOTTOM BOTTOM + 1150
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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 Prescaler
(fclk_I/O/8)
TOVn
TCNTn MAX - 1 MAX BOTTOM BOTTOM + 1
clkI/O
clkTn
(clkI/O/8)
OCFnx
OCRnx
TCNTn
OCRnx Value
OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2
clkI/O
clkTn
(clkI/O/8)
OCFnx
OCRnx
TCNTn
(CTC)
TOP
TOP - 1 TOP BOTTOM BOTTOM + 1
clkI/O
clkTn
(clkI/O/8)151
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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 reentering
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 Powersave
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 startup,
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 152
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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 Powersave
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 applying
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
clkT2153
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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 predictable
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 ensuring
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 0 Normal 0xFF Immediate MAX
1 0 1 PWM, Phase Correct 0xFF TOP BOTTOM
2 1 0 CTC OCR2A Immediate MAX
3 1 1 Fast PWM 0xFF BOTTOM MAX154
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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 compare
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 correct
PWM mode.
Note: 1. A special case occurs when OCR2A equals TOP and COM2A1 is set. In this case, the compare
match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on
page 148 for more details.
Table 17-3. Compare Output Mode, non-PWM Mode
COM2A1 COM2A0 Description
0 0 Normal 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
0 0 Normal port operation, OC2A disconnected.
0 1 Reserved
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
0 0 Normal port operation, OC2A disconnected.
0 1 Reserved
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.155
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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 buffer
is enabled and an external clock can be input on Timer Oscillator 1 (TOSC1) pin instead of a
32kHz crystal. Writing to EXCLK should be done before asynchronous operation is selected.
Note that the crystal Oscillator will only run when this bit is zero.
Table 17-6. Clock Select Bit Description
CS22 CS21 CS20 Description
000 No clock source (Timer/Counter stopped).
0 0 1 clkT2S/(No prescaling)
0 1 0 clkT2S/8 (From prescaler)
0 1 1 clkT2S/32 (From prescaler)
1 0 0 clkT2S/64 (From prescaler)
1 0 1 clkT2S/128 (From prescaler)
1 1 0 clkT2S/256 (From prescaler)
1 1 1 clkT2S/1024 (From prescaler)
Bit 7 6 5 4 3 2 1 0
(0xB2) TCNT2[7:0] TCNT2
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 7 6 5 4 3 2 1 0
(0xB3) OCR2A[7:0] OCR2A
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 7 6 5 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 0156
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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 Oscillator
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 hardware.
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 hardware.
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 temporary
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/Counter
2 Interrupt Flag Register – TIFR2.
• Bit 0 – TOIE2: Timer/Counter2 Overflow Interrupt Enable
When the TOIE2 bit is written to one and the I-bit in the Status Register is set (one), the
Timer/Counter2 Overflow interrupt is enabled. The corresponding interrupt is executed if an
overflow in Timer/Counter2 occurs, i.e., when the TOV2 bit is set in the Timer/Counter2 Interrupt
Flag Register – TIFR2.
Bit 7 6 5 4 3 2 1 0
(0x70) – – – – – – OCIE2A TOIE2 TIMSK2
Read/Write R R R R R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0157
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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 hardware
when executing the corresponding interrupt handling vector. Alternatively, TOV2 is cleared
by writing a logic one to the flag. When the SREG I-bit, TOIE2A (Timer/Counter2 Overflow Interrupt
Enable), and TOV2 are set (one), the Timer/Counter2 Overflow interrupt is executed. In
PWM mode, this bit is set when Timer/Counter2 changes counting direction at 0x00.
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 Synchronization
Mode” on page 108 for a description of the Timer/Counter Synchronization mode.
Bit 7 6 5 4 3 2 1 0
0x17 (0x37) – – – – – – OCF2A TOV2 TIFR2
Read/Write R R R R R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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 0158
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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 simplified
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
/2/4/8/16/32/64/128159
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The interconnection between Master and Slave CPUs with SPI is shown in Figure 18-2. The system
consists of two shift Registers, and a Master clock generator. The SPI Master initiates the
communication cycle when pulling low the Slave Select SS pin of the desired Slave. Master and
Slave prepare the data to be sent in their respective shift Registers, and the Master generates
the required clock pulses on the SCK line to interchange data. Data is always shifted from Master
to Slave on the Master Out – Slave In, MOSI, line, and from Slave to Master on the Master In
– Slave Out, MISO, line. After each data packet, the Master will synchronize the Slave by pulling
high the Slave Select, SS, line.
When configured as a Master, the SPI interface has no automatic control of the SS line. This
must be handled by user software before communication can start. When this is done, writing a
byte to the SPI Data Register starts the SPI clock generator, and the hardware shifts the eight
bits into the Slave. After shifting one byte, the SPI clock generator stops, setting the end of
Transmission Flag (SPIF). If the SPI Interrupt Enable bit (SPIE) in the SPCR Register is set, an
interrupt is requested. The Master may continue to shift the next byte by writing it into SPDR, or
signal the end of packet by pulling high the Slave Select, SS line. The last incoming byte will be
kept in the Buffer Register for later use.
When configured as a Slave, the SPI interface will remain sleeping with MISO tri-stated as long
as the SS pin is driven high. In this state, software may update the contents of the SPI Data
Register, SPDR, but the data will not be shifted out by incoming clock pulses on the SCK pin
until the SS pin is driven low. As one byte has been completely shifted, the end of Transmission
Flag, SPIF is set. If the SPI Interrupt Enable bit, SPIE, in the SPCR Register is set, an interrupt
is requested. The Slave may continue to place new data to be sent into SPDR before reading
the incoming data. The last incoming byte will be kept in the Buffer Register for later use.
Figure 18-2. SPI Master-slave Interconnection
The system is single buffered in the transmit direction and double buffered in the receive direction.
This means that bytes to be transmitted cannot be written to the SPI Data Register before
the entire shift cycle is completed. When receiving data, however, a received character must be
read from the SPI Data Register before the next character has been completely shifted in. Otherwise,
the first byte is lost.
In SPI Slave mode, the control logic will sample the incoming signal of the SCK pin. To ensure
correct sampling of the clock signal, the minimum low and high period should be:
Low period: longer than 2 CPU clock cycles.
High period: longer than 2 CPU clock cycles.
SHIFT
ENABLE160
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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 Input161
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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<>8);
UBRR0L = (unsigned char)ubrr;
/* Enable receiver and transmitter */
UCSR0B = (1<> 1) & 0x01;
return ((resh << 8) | resl);
}180
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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 buffer.
This flag is one when unread data exist in the receive buffer, and zero when the receive
buffer is empty (i.e., does not contain any unread data). If the Receiver is disabled (RXENn = 0),
the receive buffer will be flushed and consequently the RXCn bit will become zero.
When the Receive Complete Interrupt Enable (RXCIEn) in UCSRnB is set, the USART Receive
Complete interrupt will be executed as long as the RXCn Flag is set (provided that global interrupts
are enabled). When interrupt-driven data reception is used, the receive complete routine
must read the received data from UDRn in order to clear the RXCn Flag, otherwise a new interrupt
will occur once the interrupt routine terminates.
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 waiting
in the Receive Shift Register, and a new start bit is detected. If the DORn Flag is set there
was one or more serial frame lost between the frame last read from UDRn, and the next frame
read from UDRn. For compatibility with future devices, always write this bit to zero when writing
to UCSRnA. The DORn Flag is cleared when the frame received was successfully moved from
the Shift Register to the receive buffer.
The Parity Error (UPEn) Flag indicates that the next frame in the receive buffer had a Parity
Error when received. If Parity Check is not enabled the UPEn bit will always be read zero. For
compatibility with future devices, always set this bit to zero when writing to UCSRnA. For more
details see “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 Parity
Check to be performed (odd or even) is selected by the UPMn0 bit. When enabled, the Parity
Checker calculates the parity of the data bits in incoming frames and compares the result with
the parity bit from the serial frame. The result of the check is stored in the receive buffer together
with the received data and stop bits. The Parity Error (UPEn) Flag can then be read by software
to check if the frame had a Parity Error.181
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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 samples
and low pass filters each incoming bit, thereby improving the noise immunity of the
Receiver. The asynchronous reception operational range depends on the accuracy of the internal
baud rate clock, the rate of the incoming frames, and the frame size in number of bits.
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 horizontal
arrows illustrate the synchronization variation due to the sampling process. Note the
larger time variation when using the Double Speed mode (U2Xn = 1) of operation. Samples
denoted zero are samples done when the 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< 470 nF) must be connected to the LCDCAP pin as shown in Figure
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 maximum
drive time of approximately 2ms when using 1/2 or 1/4 duty, and approximately 2.7ms
1 2 3
64
63
62 LCDCAP231
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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 voltage
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 individually
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 Frame232
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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.
VLCD
GND
VLCD
1/
2VLCD
GND
VLCD
1/
2VLCD
GND
-1/
2VLCD
-VLCD
SEG0
COM0
SEG0 - COM0
Frame Frame
VLCD
GND
VLCD
1/
2VLCD
GND
VLCD
1/
2VLCD
GND
-1/
2VLCD
-VLCD
SEG0
COM1
SEG0 - COM1
Frame Frame
VLCD
2/
3VLCD 1/
3VLCD
GND
VLCD
2/
3VLCD 1/
3VLCD
GND
VLCD 2/
3VLCD 1/
3VLCD
GND
-1/
3VLCD
-2/
3VLCD
-VLCD
SEG0
COM0
SEG0 - COM0
Frame Frame
VLCD
2/
3VLCD 1/
3VLCD
GND
VLCD
2/
3VLCD 1/
3VLCD
GND
VLCD 2/
3VLCD 1/
3VLCD
GND
-1/
3VLCD
-2/
3VLCD
-VLCD
SEG0
COM1
SEG0 - COM1
Frame Frame233
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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.
VLCD
2/
3VLCD
1/
3VLCD
GND
VLCD
2/
3VLCD
1/
3VLCD
GND
VLCD
2/
3VLCD
1/
3VLCD
GND
-1/
3VLCD
-2/
3VLCD
-VLCD
SEG0
COM0
SEG0 - COM0
Frame Frame
VLCD
2/
3VLCD
1/
3VLCD
GND
VLCD
2/
3VLCD
1/
3VLCD
GND
VLCD
2/
3VLCD
1/
3VLCD
GND
-1/
3VLCD
-2/
3VLCD
-VLCD
SEG0
COM1
SEG0 - COM1
Frame Frame
VLCD 2/
3VLCD 1/
3VLCD
GND
VLCD 2/
3VLCD
1/
3VLCD
GND
VLCD 2/
3VLCD
1/
3VLCD
GND
-1/
3VLCD
-2/
3VLCD
-VLCD
SEG0
COM0
SEG0 - COM0
Frame Frame
VLCD 2/
3VLCD 1/
3VLCD
GND
VLCD 2/
3VLCD
1/
3VLCD
GND
VLCD 2/
3VLCD
1/
3VLCD
GND
-1/
3VLCD
-2/
3VLCD
-VLCD
SEG0
COM0
SEG0 - COM0
Frame Frame234
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When EXCLK in ASSR Register is written to one, and asynchronous clock is selected, the external
clock input buffer is enabled and an external clock can be input on Timer Oscillator 1
(TOSC1) pin instead of a 32kHz crystal. 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 synchronous
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 segments
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.235
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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 process
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
2e 2c
2f
2d
2g
COM3
COM0 COM1 COM2
SEG0
SEG1
SEG2
1b,1c
2c
2f
2a
2d
2g
2b
2e
..
COM2
SEG0
SEG1
SEG2
ATmega329 COM0 COM1
Connection table
LCD
51 50 49
48
47
46
45236
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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< 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 following
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 systems,
the programmer can not guarantee that SCK is held low during power-up. In this
case, RESET must be given a positive pulse of at least two CPU clock cycles duration
after SCK has been set to “0”.
2. Wait for at least 20ms and enable serial programming by sending the Programming
Enable serial instruction to pin MOSI.
3. The serial programming instructions will not work if the communication is out of synchronization.
When in sync. the second byte (0x53), will echo back when issuing the third
byte of the Programming Enable instruction. Whether the echo is correct or not, all four
bytes of the instruction must be transmitted. If the 0x53 did not echo back, give RESET a
positive pulse and issue a new Programming Enable command.
4. The Flash is programmed one page at a time. The 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 content
at the selected address at serial output MISO.
7. At the end of the programming session, RESET can be set high to commence normal
operation.310
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8. Power-off sequence (if needed):
Set RESET to “1”.
Turn VCC 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 $28 adr MSB adr LSB high data byte out
Read Program Memory, Low byte $20 adr MSB adr LSB low data byte out
Read EEPROM Memory $A0 0000 00aa
/
0000 0aaa
aaaa aaaa data byte out311
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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 Byte4312
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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
Adr MSB Adr LSB313
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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-System
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 dedicated
for this purpose.
During programming the clock frequency of the TCK Input must be less than the maximum frequency
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 27-13.314
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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
0 11 1
0 0
0 0
1 1
1 0
1
1
0
1
0
0
1 0
1
1
0
1
0
0
0 0
1 1315
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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 “Programming
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 Register316
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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 contents
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
= D Q
ClockDR & PROG_ENABLE
Programming Enable
0xA370317
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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 Bits318
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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)319
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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 Notes320
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ATmega329/3290/649/6490
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 Notes321
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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 register.
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 CapTest-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
0 11 1
0 0
0 0
1 1
1 0
1
1
0
1
0
0
1 0
1
1
0
1
0
0
0 0
1 1322
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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 Register
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 Programming
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 programming
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
Machine323
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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 Register
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.324
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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.325
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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 corresponding
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.326
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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 damage
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
I
OL = 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) 1 µA
IIH
Input Leakage
Current I/O Pin
VCC = 5.5V, pin high
(absolute value) 1 µA
RRST Reset Pull-up Resistor 20 100 kΩ
RPU I/O Pin Pull-up Resistor 20 100 kΩ327
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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. Units328
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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 Area329
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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%
VIL1
VIH1
Table 28-3. External Clock Drive
Symbol Parameter
VCC=1.8-5.5V VCC=2.7-5.5V VCC=4.5-5.5V
Min. Max. Min. Max. Min. Max. Units
1/tCLCL
Oscillator
Frequency 040 8 0 16 MHz
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
2 2 2%330
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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
t
RST 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
t
BG
Bandgap reference start-up time VCC = 2.7V,
TA = 25°C 40 70 µs
I
BG
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 1.8 2.0
01 2.5 2.7 2.9 V
00 4.1 4.3 4.5331
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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
5 Hold Master 10
6 Out to SCK Master 0.5 • tsck
7 SCK to out Master 10
8 SCK to out high Master 10
9 SS 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
18 SS low to SCK Slave 20 • tck
MOSI
(Data Output)
SCK
(CPOL = 1)
MISO
(Data Input)
SCK
(CPOL = 0)
SS
MSB LSB
MSB LSB
...
...
6 1
2 2
4 5 3
7 8332
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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
MSB LSB
...
...
10
11 11
13 14 12
15 17
9
X
16333
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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 8 Bits
Absolute accuracy (Including
INL, DNL, quantization error,
gain and offset error)
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
2 2.5 LSB
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
2 LSB
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
2 LSB
Offset Error
Single Ended Conversion
VREF = 4V, VCC = 4V,
ADC clock = 200kHz
2 LSB
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 GND VREF V
Differential Channels GND AVCC V
Input Range
Single Ended Channels GND VREF V
Differential Channels(1) -0.85VREF VREF V
Input Bandwidth
Single Ended Channels 38.5 kHz
Differential Channels 4 kHz334
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Note: 1. Voltage difference between channels.
28.8 LCD Controller Characteristics
VINT Internal Voltage Reference 1.0 1.1 1.2 V
RREF Reference Input Resistance 32 kΩ
RAIN Analog 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 Units335
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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 disabled
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 temperature.
The dominating factors are operating voltage and frequency.
The current drawn from capacitive loaded pins may be estimated (for one pin) as CL*VCC*f where
CL = load capacitance, VCC = operating voltage and f = average switching frequency of I/O pin.
The parts are characterized at frequencies higher than test limits. Parts are not guaranteed to
function properly at frequencies higher than the ordering code indicates.
The difference between current consumption in Power-down mode with Watchdog Timer
enabled and Power-down mode with Watchdog Timer disabled represents the differential current
drawn by the Watchdog Timer.
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 0.9 1
Frequency (MHz)
ICC (m A)336
2552K–AVR–04/11
ATmega329/3290/649/6490
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
0 2 4 6 8 10 12 14 16
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
VCC (V)
ICC (mA)
85°C
25°C
-40°C337
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ATmega329/3290/649/6490
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
VCC (V)
ICC (uA)338
2552K–AVR–04/11
ATmega329/3290/649/6490
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 0.9 1
Frequency (MHz)
ICC (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
0 2 4 6 8 10 12 14 16
Frequency (MHz)
ICC (mA)
1.8 V339
2552K–AVR–04/11
ATmega329/3290/649/6490
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,
1 MHz)
0
1
2
3
4
5
6
7
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (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
VCC (V)
ICC (mA)
85 C°
25 C°
-40 C°340
2552K–AVR–04/11
ATmega329/3290/649/6490
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
VCC (V)
ICC (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%341
2552K–AVR–04/11
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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 consumption
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 • ( ) 1 0.0 + ++ 85 0.09 0.048 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
VCC (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)
ICC (uA)342
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ATmega329/3290/649/6490
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
VCC (V)
ICC (uA)343
2552K–AVR–04/11
ATmega329/3290/649/6490
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
VIO (V)
IIO (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°C344
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°C345
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
VRESET (V)
IRESET (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
VRESET (V)
IRESET (uA)
-40°C
25°C
85°C346
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
VOH (V)
IOH (mA)
85°C
25°C
-40°C
0
5
10
15
20
25
0 0.5 1 1.5 2 2.5 3
VOH (V)
IOH (mA)
85°C
25°C
-40°C347
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
VOH (V)
IOH (mA)
85°C
25°C
-40°C348
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
VOH (V)
IOH (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
VOH (V)
IOH (mA)
85°C
25°C
-40°C349
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
VOL (V)
IOL (mA)
85°C
25°C
-40°C350
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
VOL (V)
IOL (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
VOL (V)
IOL (mA)
85°C
25°C
-40°C351
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
VOL (V)
IOL (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
VOL (V)
IOL (mA)
85°C
25°C
-40°C352
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
VCC (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
VCC (V)
Threshold (V)
85°C
25°C
-40°C353
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
VCC (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
VCC (V)
Threshold (V)
85°C
25°C
-40°C354
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
VCC (V)
Input Hysteresis (V)
85°C
25°C
-40°C355
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 VCC
Falling VCC
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 VCC
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 VCC
Falling VCC
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
VCC (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
0 -40°C
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
VCC (V)
FRC (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)
FRC (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
VCC (V)
FRC (MHz)
85 °C
25 °C
-40 °C
4
6
8
10
12
14
16
0 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256
OSCCAL VALUE
FRC (M Hz)360
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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
VCC (V)
ICC (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°C361
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°C362
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
VCC (V)
ICC (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°C363
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
VCC (V)
ICC (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 0.9 1
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
0 2 4 6 8 10 12 14 16
Frequency (MHz)
ICC (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°C365
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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) LCDDR18 SEG331 SEG330 SEG329 SEG328 SEG327 SEG326 SEG325 SEG324 244
(0xFD) LCDDR17 SEG323 SEG322 SEG321 SEG320 SEG319 SEG318 SEG317 SEG316 244
(0xFC) LCDDR16 SEG315 SEG314 SEG313 SEG312 SEG311 SEG310 SEG309 SEG308 244
(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 SEG218 SEG217 SEG216 244
(0xF7) LCDDR11 SEG215 SEG214 SEG213 SEG212 SEG211 SEG210 SEG209 SEG208 244
(0xF6) LCDDR10 SEG207 SEG206 SEG205 SEG204 SEG203 SEG202 SEG201 SEG200 244
(0xF5) LCDDR09 SEG139 SEG138 SEG137 SEG136 SEG135 SEG134 SEG133 SEG132 244
(0xF4) LCDDR08 SEG131 SEG130 SEG129 SEG128 SEG127 SEG126 SEG125 SEG124 244
(0xF3) LCDDR07 SEG123 SEG122 SEG121 SEG120 SEG119 SEG118 SEG117 SEG116 244
(0xF2) LCDDR06 SEG115 SEG114 SEG113 SEG112 SEG111 SEG110 SEG109 SEG108 244
(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 SEG018 SEG017 SEG016 244
(0xED) LCDDR01 SEG015 SEG014 SEG013 SEG012 SEG011 SEG010 SEG009 SEG008 244
(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 - - LCDBL 239
(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 194366
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 RXEN0 TXEN0 UCSZ02 RXB80 TXB80 191
(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 Page367
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 - WGM13 WGM12 CS12 CS11 CS10 134
(0x80) TCCR1A COM1A1 COM1A0 COM1B1 COM1B0 - - WGM11 WGM10 132
(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 PCINT8 58
(0x6B) PCMSK0 PCINT7 PCINT6 PCINT5 PCINT4 PCINT3 PCINT2 PCINT1 PCINT0 58
(0x6A) Reserved - - - - - - - -
(0x69) EICRA - - - - - - ISC01 ISC00 55
(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 N Z C 12
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 SPMEN 291
0x36 (0x56) Reserved
0x35 (0x55) MCUCR JTD - - PUD - - IVSEL IVCE 52/87/254
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 Page368
2552K–AVR–04/11
ATmega329/3290/649/6490
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 - - - - - - OCF2A TOV2 157
0x16 (0x36) TIFR1 - - ICF1 - - OCF1B OCF1A TOV1 138
0x15 (0x35) TIFR0 - - - - - - OCF0A TOV0 106
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) PINF PINF7 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) PINE PINE7 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) PIND PIND7 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) PINC PINC7 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) PINB PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 87
0x02 (0x22) PORTA PORTA7 PORTA6 PORTA5 PORTA4 PORTA3 PORTA2 PORTA1 PORTA0 87
0x01 (0x21) DDRA DDA7 DDA6 DDA5 DDA4 DDA3 DDA2 DDA1 DDA0 87
0x00 (0x20) PINA PINA7 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 Page369
2552K–AVR–04/11
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 • K Z,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 1/2370
2552K–AVR–04/11
ATmega329/3290/649/6490
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 ← 1 C1
CLC Clear Carry C ← 0 C 1
SEN Set Negative Flag N ← 1 N 1
CLN Clear Negative Flag N ← 0 N 1
SEZ Set Zero Flag Z ← 1 Z1
CLZ Clear Zero Flag Z ← 0 Z 1
SEI Global Interrupt Enable I ← 1 I1
CLI Global Interrupt Disable I ← 0 I 1
SES Set Signed Test Flag S ← 1 S1
CLS Clear Signed Test Flag S ← 0 S 1
SEV Set Twos Complement Overflow. V ← 1 V1
CLV Clear Twos Complement Overflow V ← 0 V 1
SET Set T in SREG T ← 1 T1
CLT Clear T in SREG T ← 0 T 1
SEH Set Half Carry Flag in SREG H ← 1 H1
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 #Clocks371
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ATmega329/3290/649/6490
IN Rd, 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 #Clocks372
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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 directive).
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
8 1.8 - 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 directive).
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
8 1.8 - 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 directive).
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
8 1.8 - 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 directive).
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
8 1.8 - 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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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) 64A C
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 TYP377
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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, 64M1 H
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 0.18 0.25 0.30
D
D2 5.20 5.40 5.60
8.90 9.00 9.10
E 8.90 9.00 9.10
E2 5.20 5.40 5.60
e 0.50 BSC
L 0.35 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
0.08 C
1
2
3
K 1.25 1.40 1.55
E2
D2
b e
Pin #1 Corner L
Pin #1
Triangle
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) 378
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ATmega329/3290/649/6490
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) 100A D
2010-10-20
PIN 1 IDENTIFIER
0°~7°
PIN 1
L
C
A1 A2 A
D1
D
e E1 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 NOTE379
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ATmega329/3290/649/6490
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).380
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ATmega329/3290/649/6490
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).381
2552K–AVR–04/11
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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
2552K–AVR–04/11
ATmega329/3290/649/6490
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 329.383
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ATmega329/3290/649/6490
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 334.384
2552K–AVR–04/11
ATmega329/3290/649/6490
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.i
2552K–AVR–04/11
ATmega329/3290/649/6490
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
6.8 Reset 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 .................................................................................................31ii
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8.7 Clock Output Buffer .........................................................................................31
8.8 Timer/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
9.8 Register 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
10.8 Watchdog 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 ..................................................................................65iii
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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
14.8 Timer/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
16.8 Compare 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
17.8 Timer/Counter Timing Diagrams ...................................................................149
17.9 Asynchronous Operation of Timer/Counter2 .................................................151iv
2552K–AVR–04/11
ATmega329/3290/649/6490
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
19.8 Asynchronous 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 ....................................................................................213v
2552K–AVR–04/11
ATmega329/3290/649/6490
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
24.8 Using 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
25.8 Boundary-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 ................................................................282vi
2552K–AVR–04/11
ATmega329/3290/649/6490
26.6 Addressing the Flash During Self-Programming ...........................................283
26.7 Self-Programming the Flash ..........................................................................283
26.8 Register 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
27.8 Programming 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
28.8 LCD 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 ..............................................................................................................378vii
2552K–AVR–04/11
ATmega329/3290/649/6490
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
35.8 Rev. 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....................................................................................... i2552K–AVR–04/11
Atmel Corporation
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© 2011 Atmel Corporation. All rights reserved.
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subsidiaries. Other terms and product names may be trademarks of others.
Disclaimer: The information in this document is provided in connection with Atmel products. No license, express or implied, by estoppel or otherwise, to
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Features
• High Performance, Low Power AVR® 8-Bit Microcontroller
• Advanced RISC Architecture
– 120 Powerful Instructions – Most Single Clock Cycle Execution
– 32 x 8 General Purpose Working Registers
– Fully Static Operation
– Up to 20 MIPS Throughput at 20 MHz
• Data and Non-volatile Program and Data Memories
– 2/4K Bytes of In-System Self Programmable Flash
• Endurance 10,000 Write/Erase Cycles
– 128/256 Bytes In-System Programmable EEPROM
• Endurance: 100,000 Write/Erase Cycles
– 128/256 Bytes Internal SRAM
– Programming Lock for Flash Program and EEPROM Data Security
• Peripheral Features
– One 8-bit Timer/Counter with Separate Prescaler and Compare Mode
– One 16-bit Timer/Counter with Separate Prescaler, Compare and Capture Modes
– Four PWM Channels
– On-chip Analog Comparator
– Programmable Watchdog Timer with On-chip Oscillator
– USI – Universal Serial Interface
– Full Duplex USART
• Special Microcontroller Features
– debugWIRE On-chip Debugging
– In-System Programmable via SPI Port
– External and Internal Interrupt Sources
– Low-power Idle, Power-down, and Standby Modes
– Enhanced Power-on Reset Circuit
– Programmable Brown-out Detection Circuit
– Internal Calibrated Oscillator
• I/O and Packages
– 18 Programmable I/O Lines
– 20-pin PDIP, 20-pin SOIC, 20-pad MLF/VQFN
• Operating Voltage
– 1.8 – 5.5V
• Speed Grades
– 0 – 4 MHz @ 1.8 – 5.5V
– 0 – 10 MHz @ 2.7 – 5.5V
– 0 – 20 MHz @ 4.5 – 5.5V
• Industrial Temperature Range: -40°C to +85°C
• Low Power Consumption
– Active Mode
• 190 µA at 1.8V and 1MHz
– Idle Mode
• 24 µA at 1.8V and 1MHz
– Power-down Mode
• 0.1 µA at 1.8V and +25°C
8-bit
Microcontroller
with 2/4K Bytes
In-System
Programmable
Flash
ATtiny2313A
ATtiny4313
Rev. 8246B–AVR–09/112
8246B–AVR–09/11
ATtiny2313A/4313
1. Pin Configurations
Figure 1-1. Pinout ATtiny2313A/4313
(PCINT10/RESET/dW) PA2
(PCINT11/RXD) PD0
(PCINT12/TXD) PD1
(PCINT9/XTAL2) PA1
(PCINT8/CLKI/XTAL1) PA0
(PCINT13/CKOUT/XCK/INT0) PD2
(PCINT14/INT1) PD3
(PCINT15/T0) PD4
(PCINT16/OC0B/T1) PD5
GND
20
19
18
17
16
15
14
13
12
11
1
2
3
4
5
6
7
8
9
10
VCC
PB7 (USCK/SCL/SCK/PCINT7)
PB6 (MISO/DO/PCINT6)
PB5 (MOSI/DI/SDA/PCINT5)
PB4 (OC1B/PCINT4)
PB3 (OC1A/PCINT3)
PB2 (OC0A/PCINT2)
PB1 (AIN1/PCINT1)
PB0 (AIN0/PCINT0)
PD6 (ICPI/PCINT17)
PDIP/SOIC
1
2
3
4
5
MLF/VQFN
15
14
13
12
11
20
19
18
17
16
6
7
8
9
10
(PCINT12/TXD) PD1
(PCINT9/XTAL2) PA1
(PCINT8/CLKI/XTAL1) PA0
(PCINT13/CKOUT/XCK/INT0) PD2
(PCINT14/INT1) PD3
(PCINT15/T0) PD4
(PCINT16/OC0B/T1) PD5
GND
(PCINT17/ICPI) PD6
(AIN0/PCINT0) PB0
PB5 (MOSI/DI/SDA/PCINT5)
PB4 (OC1B/PCINT4)
PB3 (OC1A/PCINT3)
PB2 (OC0A/PCINT2)
PB1 (AIN1/PCINT1)
PD0 (RXD/PCINT11)
PA2 (RESET/dW/PCINT10)
VCC
PB7 (USCK/SCL/SCK/PCINT7)
PB6 (MISO/DO/PCINT6)
NOTE: Bottom pad should be soldered to ground.3
8246B–AVR–09/11
ATtiny2313A/4313
1.1 Pin Descriptions
1.1.1 VCC
Digital supply voltage.
1.1.2 GND
Ground.
1.1.3 Port A (PA2..PA0)
Port A is a 3-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, except PA2 which has the RESET capability. To use pin PA2 as I/O pin, instead of
RESET pin, program (“0”) RSTDISBL fuse. 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 ATtiny2313A/4313 as listed on
page 62.
1.1.4 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 also serves the functions of various special features of the ATtiny2313A/4313 as listed on
page 63.
1.1.5 Port D (PD6..PD0)
Port D is a 7-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 ATtiny2313A/4313 as listed on
page 67.
1.1.6 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 and provided that the reset pin has not been disabled. The
minimum pulse length is given in Table 22-3 on page 201. Shorter pulses are not guaranteed to
generate a reset. The Reset Input is an alternate function for PA2 and dW.
The reset pin can also be used as a (weak) I/O pin.
1.1.7 XTAL1
Input to the inverting Oscillator amplifier and input to the internal clock operating circuit. XTAL1
is an alternate function for PA0.4
8246B–AVR–09/11
ATtiny2313A/4313
1.1.8 XTAL2
Output from the inverting Oscillator amplifier. XTAL2 is an alternate function for PA1.5
8246B–AVR–09/11
ATtiny2313A/4313
2. Overview
The ATtiny2313A/4313 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced
RISC architecture. By executing powerful instructions in a single clock cycle, the
ATtiny2313A/4313 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
PROGRAM
FLASH
INSTRUCTION
REGISTER
GND
VCC
INSTRUCTION
DECODER
CONTROL
LINES
STACK
POINTER
SRAM
GENERAL
PURPOSE
REGISTER
ALU
STATUS
REGISTER
PROGRAMMING
LOGIC SPI
8-BIT DATA BUS
XTAL1 XTAL2
RESET
INTERNAL
OSCILLATOR
OSCILLATOR
WATCHDOG
TIMER
TIMING AND
CONTROL
MCU CONTROL
REGISTER
MCU STATUS
REGISTER
TIMER/
COUNTERS
INTERRUPT
UNIT
EEPROM
USI
USART
ANALOG
COMPARATOR
DATA REGISTER
PORTB
DATA DIR.
REG. PORTB
DATA REGISTER
PORTA
DATA DIR.
REG. PORTA
PORTB DRIVERS
PB0 - PB7
PORTA DRIVERS
PA0 - PA2
DATA REGISTER
PORTD
DATA DIR.
REG. PORTD
PORTD DRIVERS
PD0 - PD6
ON-CHIP
DEBUGGER
INTERNAL
CALIBRATED
OSCILLATOR6
8246B–AVR–09/11
ATtiny2313A/4313
The AVR core combines a rich instruction set with 32 general purpose working registers. All the
32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent
registers to be accessed in one single instruction executed in one clock cycle. The resulting
architecture is more code efficient while achieving throughputs up to ten times faster than conventional
CISC microcontrollers.
The ATtiny2313A/4313 provides the following features: 2/4K bytes of In-System Programmable
Flash, 128/256 bytes EEPROM, 128/256 bytes SRAM, 18 general purpose I/O lines, 32 general
purpose working registers, a single-wire Interface for On-chip Debugging, two flexible
Timer/Counters with compare modes, internal and external interrupts, a serial programmable
USART, Universal Serial Interface with Start Condition Detector, a programmable Watchdog
Timer with internal Oscillator, and three software selectable power saving modes. The Idle mode
stops the CPU while allowing the SRAM, Timer/Counters, and interrupt system to continue functioning.
The Power-down mode saves the register contents but freezes the Oscillator, disabling
all other chip functions until the next interrupt or hardware reset. In Standby mode, the crystal/resonator
Oscillator is running while the rest of the device is sleeping. This allows very fast
start-up combined with low-power consumption.
The device is manufactured using Atmel’s high density non-volatile memory technology. The
On-chip ISP Flash allows the program memory to be reprogrammed In-System through an SPI
serial interface, or by a conventional non-volatile memory programmer. By combining an 8-bit
RISC CPU with In-System Self-Programmable Flash on a monolithic chip, the Atmel
ATtiny2313A/4313 is a powerful microcontroller that provides a highly flexible and cost effective
solution to many embedded control applications.
The ATtiny2313A/4313 AVR is supported with a full suite of program and system development
tools including: C Compilers, Macro Assemblers, Program Debugger/Simulators, In-Circuit Emulators,
and Evaluation kits.
2.2 Comparison Between ATtiny2313A and ATtiny4313
The ATtiny2313A and ATtiny4313 differ only in memory sizes. Table 2-1 summarizes the different
memory sizes for the two devices.
Table 2-1. Memory Size Summary
Device Flash EEPROM RAM
ATtiny2313A 2K Bytes 128 Bytes 128 Bytes
ATtiny4313 4K Bytes 256 Bytes 256 Bytes7
8246B–AVR–09/11
ATtiny2313A/4313
3. About
3.1 Resources
A comprehensive set of drivers, application notes, data sheets and descriptions on development
tools are available for download at http://www.atmel.com/avr.
3.2 Code Examples
This documentation contains simple code examples that briefly show how to use various parts of
the device. These code examples assume that the part specific header file is included before
compilation. Be aware that not all C compiler vendors include bit definitions in the header files
and interrupt handling in C is compiler dependent. Please confirm with the C compiler documentation
for more details.
For I/O Registers located in the 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, this
means “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”. Note that not all
AVR devices include an extended I/O map.
3.3 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.8
8246B–AVR–09/11
ATtiny2313A/4313
4. CPU Core
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.
4.1 Architectural Overview
Figure 4-1. Block Diagram of the AVR Architecture
In order to maximize performance and parallelism, the AVR uses a Harvard architecture – with
separate memories and buses for program and data. Instructions in the program memory are
executed with a single level pipelining. While one instruction is being executed, the next instruction
is pre-fetched from the program memory. This concept enables instructions to be executed
in every clock cycle. The program memory is In-System Reprogrammable Flash memory.
The fast-access Register File contains 32 x 8-bit general purpose working registers with a single
clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU) operation. In a typical
ALU operation, two operands are output from the Register File, the operation is executed,
and the result is stored back in the Register File – in one clock cycle.
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 n9
8246B–AVR–09/11
ATtiny2313A/4313
Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data
Space addressing – enabling efficient address calculations. One of the these address pointers
can also be used as an address pointer for look up tables in Flash program memory. These
added function registers are the 16-bit X-, Y-, and Z-register, described later in this section.
The ALU supports arithmetic and logic operations between registers or between a constant and
a register. Single register operations can also be executed in the ALU. After an arithmetic operation,
the Status Register is updated to reflect information about the result of the operation.
Program flow is provided by conditional and unconditional jump and call instructions, able to
directly address the whole address space. Most AVR instructions have a single 16-bit word format.
Every program memory address contains a 16- or 32-bit instruction.
During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the
Stack. The Stack is effectively allocated in the general data SRAM, and consequently the Stack
size is only limited by the total SRAM size and the usage of the SRAM. All user programs must
initialize the SP in the Reset routine (before subroutines or interrupts are executed). The Stack
Pointer (SP) is read/write accessible in the I/O space. The data SRAM can easily be accessed
through the five different addressing modes supported in the AVR architecture.
The memory spaces in the AVR architecture are all linear and regular memory maps.
A flexible interrupt module has its control registers in the I/O space with an additional Global
Interrupt Enable bit in the Status Register. All interrupts have a separate Interrupt Vector in the
Interrupt Vector table. The interrupts have priority in accordance with their Interrupt Vector position.
The lower the Interrupt Vector address, the higher the priority.
The I/O memory space contains 64 addresses for CPU peripheral functions as Control Registers,
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.
4.2 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.
4.3 Status Register
The Status Register contains information about the result of the most recently executed arithmetic
instruction. This information can be used for altering program flow in order to perform
conditional operations. Note that the Status Register is updated after all ALU operations, as
specified in the Instruction Set Reference. This will in many cases remove the need for using the
dedicated compare instructions, resulting in faster and more compact code.
The Status Register is not automatically stored when entering an interrupt routine and restored
when returning from an interrupt. This must be handled by software.10
8246B–AVR–09/11
ATtiny2313A/4313
The AVR Status Register – SREG – is defined as:
• Bit 7 – I: Global Interrupt Enable
The Global Interrupt Enable bit must be set for the interrupts to be enabled. The individual interrupt
enable control is then performed in separate control registers. If the Global Interrupt Enable
Register is cleared, none of the interrupts are enabled independent of the individual interrupt
enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is set by
the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared by
the application with the SEI and CLI instructions, as described in the instruction set reference.
• Bit 6 – T: Bit Copy Storage
The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or destination
for the operated bit. A bit from a register in the Register File can be copied into T by the
BST instruction, and a bit in T can be copied into a bit in a register in the Register File by the
BLD instruction.
• Bit 5 – H: Half Carry Flag
The Half Carry Flag H indicates a Half Carry in some arithmetic operations. Half Carry Is useful
in BCD arithmetic. See the “Instruction Set Description” for detailed information.
• Bit 4 – S: Sign Bit, S = N ⊕ V
The S-bit is always an exclusive or between the negative flag N and the Two’s Complement
Overflow Flag V. See the “Instruction Set Description” for detailed information.
• Bit 3 – V: Two’s Complement Overflow Flag
The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See the
“Instruction Set Description” for detailed information.
• Bit 2 – N: Negative Flag
The Negative Flag N indicates a negative result in an arithmetic or logic operation. See the
“Instruction Set Description” for detailed information.
• Bit 1 – Z: Zero Flag
The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction
Set Description” for detailed information.
• Bit 0 – C: Carry Flag
The Carry Flag C indicates a carry in an arithmetic or logic operation. See the “Instruction Set
Description” for detailed information.
Bit 7 6 5 4 3 2 1 0
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 0 011
8246B–AVR–09/11
ATtiny2313A/4313
4.4 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 4-2 shows the structure of the 32 general purpose working registers in the CPU.
Figure 4-2. 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 4-2, 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 implemented
as SRAM locations, this memory organization provides great flexibility in access of the
registers, as the X-, Y- and Z-pointer registers can be set to index any register in the file.
4.4.1 The X-register, Y-register, and Z-register
The registers R26..R31 have some added functions to their general purpose usage. These registers
are 16-bit address pointers for indirect addressing of the data space. The three indirect
address registers X, Y, and Z are defined as described in Figure 4-3.
7 0 Addr.
R0 0x00
R1 0x01
R2 0x02
…
R13 0x0D
General R14 0x0E
Purpose R15 0x0F
Working R16 0x10
Registers R17 0x11
…
R26 0x1A X-register Low Byte
R27 0x1B X-register High Byte
R28 0x1C Y-register Low Byte
R29 0x1D Y-register High Byte
R30 0x1E Z-register Low Byte
R31 0x1F Z-register High Byte12
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Figure 4-3. 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).
4.5 Stack Pointer
The Stack is mainly used for storing temporary data, for storing local variables and for storing
return addresses after interrupts and subroutine calls. The Stack Pointer Register always points
to the top of the Stack. Note that the Stack is implemented as growing from higher memory locations
to lower memory locations. This implies that a Stack PUSH command decreases the Stack
Pointer.
The Stack Pointer points to the data SRAM Stack area where the Subroutine and Interrupt
Stacks are located. This Stack space in the data SRAM must be defined by the program before
any subroutine calls are executed or interrupts are enabled. The Stack Pointer must be set to
point above 0x60. The Stack Pointer is decremented by one when data is pushed onto the Stack
with the PUSH instruction, and it is decremented by two when the return address is pushed onto
the Stack with subroutine call or interrupt. The Stack Pointer is incremented by one when data is
popped from the Stack with the POP instruction, and it is incremented by two when data is
popped from the Stack with return from subroutine RET or return from interrupt RETI.
The Stack Pointer is implemented as one 8-bit register in the I/O space.
4.6 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 4-4 shows the parallel instruction fetches and instruction executions enabled by the Harvard
architecture and the fast-access Register File concept. This is the basic pipelining concept
to obtain up to 1 MIPS per MHz with the corresponding unique results for functions per cost,
functions per clocks, and functions per power-unit.
15 XH XL 0
X-register 7 07 0
R27 (0x1B) R26 (0x1A)
15 YH YL 0
Y-register 7 07 0
R29 (0x1D) R28 (0x1C)
15 ZH ZL 0
Z-register 70 7 0
R31 (0x1F) R30 (0x1E)
Bit 7 6 5 4 3 2 1 0
0x3D (0x5D) SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SPL
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND RAMEND13
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Figure 4-4. The Parallel Instruction Fetches and Instruction Executions
Figure 4-5 shows the internal timing concept for the Register File. In a single clock cycle an ALU
operation using two register operands is executed, and the result is stored back to the destination
register.
Figure 4-5. Single Cycle ALU Operation
4.7 Reset and Interrupt Handling
The AVR provides several different interrupt sources. These interrupts and the separate Reset
Vector each have a separate program vector in the program memory space. All interrupts are
assigned individual enable bits which must be written logic one together with the Global Interrupt
Enable bit in the Status Register in order to enable the interrupt.
The lowest addresses in the program memory space are by default defined as the Reset and
Interrupt Vectors. The complete list of vectors is shown in “Interrupts” on page 48. The list also
determines the priority levels of the different interrupts. The lower the address the higher is the
priority level. RESET has the highest priority, and next is INT0 – the External Interrupt Request
0. Refer to “Interrupts” on page 48 for more information.
When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts are disabled.
The user software can write logic one to the I-bit to enable nested interrupts. All enabled
interrupts can then interrupt the current interrupt routine. The I-bit is automatically set when a
Return from Interrupt instruction – RETI – is executed.
There are basically two types of interrupts. The first type is triggered by an event that sets the
interrupt flag. For these interrupts, the Program Counter is vectored to the actual Interrupt Vector
in order to execute the interrupt handling routine, and hardware clears the corresponding interrupt
flag. Interrupt flags can also be cleared by writing a logic one to the flag bit position(s) to be
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
clkCPU14
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cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is cleared,
the interrupt flag will be set and remembered until the interrupt is enabled, or the flag is cleared
by software. Similarly, if one or more interrupt conditions occur while the Global Interrupt Enable
bit is cleared, the corresponding interrupt flag(s) will be set and remembered until the Global
Interrupt Enable bit is set, and will then be executed by order of priority.
The second type of interrupts will trigger as long as the interrupt condition is present. These
interrupts do not necessarily have interrupt flags. If the interrupt condition disappears before the
interrupt is enabled, the interrupt will not be triggered.
When the AVR exits from an interrupt, it will always return to the main program and execute one
more instruction before any pending interrupt is served.
Note that the Status Register is not automatically stored when entering an interrupt routine, nor
restored when returning from an interrupt routine. This must be handled by software.
When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled.
No interrupt will be executed after the CLI instruction, even if it occurs simultaneously with the
CLI instruction. The following example shows how this can be used to avoid interrupts during the
timed EEPROM write sequence..
When using the SEI instruction to enable interrupts, the instruction following SEI will be executed
before any pending interrupts, as shown in this example.
Assembly Code Example
in r16, SREG ; store SREG value
cli ; disable interrupts during timed sequence
sbi EECR, EEMPE ; start EEPROM write
sbi EECR, EEPE
out SREG, r16 ; restore SREG value (I-bit)
C Code Example
char cSREG;
cSREG = SREG; /* store SREG value */
/* disable interrupts during timed sequence */
__disable_interrupt();
EECR |= (1<