Atmel Electronic Components Datasheet



ATmega1284

8-bit Atmel Microcontroller


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ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P
8-bit Atmel Microcontroller with 16/32/64/128K Bytes
In-System Programmable Flash
DATASHEET
Features
High-performance, low-power 8-bit Atmel® AVR® Microcontroller
Advanced RISC architecture
̶ 131 powerful Instructions – most single-clock cycle execution
̶ 32 × 8 general purpose working registers
̶ Fully static operation
̶ Up to 20MIPS throughput at 20MHz
̶ On-chip 2-cycle multiplier
High endurance non-volatile memory segments
̶ 16/32/64/128KBytes of In-System Self-programmable Flash program memory
̶ 512/1K/2K/4KBytes EEPROM
̶ 1/2/4/16KBytes Internal SRAM
̶ 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
Atmel QTouch® library support
̶ Capacitive touch buttons, sliders and wheels
̶ QTouch and QMatrix acquisition
̶ Up to 64 sense channels
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
̶ Two 8-bit Timer/Counters with Separate Prescalers and Compare Modes
̶ One/two 16-bit Timer/Counter with Separate Prescaler, Compare Mode, and
Capture Mode
̶ Real Time Counter with Separate Oscillator
̶ Six PWM Channels
̶ 8-channel, 10-bit ADC
Differential mode with selectable gain at 1×, 10× or 200×
̶ Byte-oriented Two-wire Serial Interface
̶ Two Programmable Serial USART
̶ Master/Slave SPI Serial Interface
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̶ 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 RC Oscillator
̶ External and Internal Interrupt Sources
̶ Six Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, Standby and Extended Standby
I/O and Packages
̶ 32 Programmable I/O Lines
̶ 40-pin PDIP, 44-lead TQFP, 44-pad VQFN/QFN/MLF
̶ 44-pad DRQFN
– 49-ball VFBGA
Operating Voltages
̶ 1.8 - 5.5V
Speed Grades
̶ 0 - 4MHz @ 1.8 - 5.5V
̶ 0 - 10MHz @ 2.7 - 5.5V
̶ 0 - 20MHz @ 4.5 - 5.5V
Power Consumption at 1MHz, 1.8V, 25C
̶ Active: 0.4mA
̶ Power-down Mode: 0.1µA
̶ Power-save Mode: 0.6µA (Including 32kHz RTC)
Note: 1. See ”Data retention” on page 9 for details.
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1. Pin configurations
1.1 Pinout - PDIP/TQFP/VQFN/QFN/MLF for
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P
Figure 1-1. Pinout.
(PCINT8/XCK0/T0) PB0
(PCINT9/CLKO/T1) PB1
(PCINT10/INT2/AIN0) PB2
(PCINT11/OC0A/AIN1) PB3
(PCINT12/OC0B/SS) PB4
(PCINT13/ICP3/MOSI) PB5
(PCINT14/OC3A/MISO) PB6
(PCINT15/OC3B/SCK) PB7
RESET
VCC
GND
XTAL2
XTAL1
(PCINT24/RXD0/T3*) PD0
(PCINT25/TXD0) PD1
(PCINT26/RXD1/INT0) PD2
(PCINT27/TXD1/INT1) PD3
(PCINT28/XCK1/OC1B) PD4
(PCINT29/OC1A) PD5
(PCINT30/OC2B/ICP) PD6
PA0 (ADC0/PCINT0)
PA1 (ADC1/PCINT1)
PA2 (ADC2/PCINT2)
PA3 (ADC3/PCINT3)
PA4 (ADC4/PCINT4)
PA5 (ADC5/PCINT5)
PA6 (ADC6/PCINT6)
PA7 (ADC7/PCINT7)
AREF
GND
AVCC
PC7 (TOSC2/PCINT23)
PC6 (TOSC1/PCINT22)
PC5 (TDI/PCINT21)
PC4 (TDO/PCINT20)
PC3 (TMS/PCINT19)
PC2 (TCK/PCINT18)
PC1 (SDA/PCINT17)
PC0 (SCL/PCINT16)
PD7 (OC2A/PCINT31)
TQFP/QFN/MLF
(PCINT13/ICP3/MOSI) PB5
(PCINT14/OC3A/MISO) PB6
(PCINT15/OC3B/SCK) PB7
RESET
VCC
GND
XTAL2
XTAL1
(PCINT24/RXD0/T3*) PD0
(PCINT25/TXD0) PD1
(PCINT26/RXD1/INT0) PD2
*T3 is only available for ATmega1284/1284P
PA4 (ADC4/PCINT4)
PA5 (ADC5/PCINT5)
PA6 (ADC6/PCINT6)
PA7 (ADC7/PCINT7)
AREF
GND
AVCC
PC7 (TOSC2/PCINT23)
PC6 (TOSC1/PCINT22)
PC5 (TDI/PCINT21)
PC4 (TDO/PCINT20)
Note: The large center pad underneath the VQFN/QFN/MLF package should be soldered to ground on the board to
ensure good mechanical stability.
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1.2 Pinout - DRQFN for Atmel ATmega164A/164PA/324A/324PA
Figure 1-2. DRQFN - pinout.
Top view
Bottom view
A1
B1
A2
B2
A3
B3
A4
B4
A5
B5
A6
A18
B15
A17
B14
A16
B13
A15
B12
A14
B11
A13
A18
B15
A17
B14
A16
B13
A15
B12
A14
B11
A13
A1
B1
A2
B2
A3
B3
A4
B4
A5
B5
A6
Table 1-1.
A1
B1
A2
B2
A3
B3
A4
B4
A5
B5
A6
DRQFN - pinout.
PB5 A7
PB6 B6
PB7 A8
RESET B7
VCC
A9
GND
B8
XTAL2
A10
XTAL1
B9
PD0 A11
PD1 B10
PD2 A12
PD3
PD4
PD5
PD6
PD7
VCC
GND
PC0
PC1
PC2
PC3
A13
B11
A14
B12
A15
B13
A16
B14
A17
B15
A18
PC4
PC5
PC6
PC7
AVCC
GND
AREF
PA7
PA6
PA5
PA4
A19
B16
A20
B17
A21
B18
A22
B19
A23
B20
A24
PA3
PA2
PA1
PA0
VCC
GND
PB0
PB1
PB2
PB3
PB4
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1.3 Pinout - VFBGA for Atmel ATmega164A/164PA/324A/324PA
Figure 1-3. VFBGA - pinout.
Top view
1234567
A
B
C
D
E
F
G
Bottom view
7654321
A
B
C
D
E
F
G
Table 1-2.
A
B
C
D
E
F
G
BGA - pinout.
12
GND
PB4
PB6 PB5
VCC
RESET
GND
XTAL2
XTAL1
PD1
PD2 PD3
GND
PD4
3
PB2
PB3
PB7
PD0
PD5
PD6
VCC
4
GND
PB0
PB1
GND
PD7
PC0
GND
5
VCC
PA0
PA1
PA4
PC5
PC2
PC1
67
PA2 GND
PA3 PA5
PA6 AREF
PA7 GND
PC7 AVCC
PC4 PC6
PC3 GND
2. Overview
The Atmel ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P 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 ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P achieves throughputs
approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing
speed.
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2.1 Block diagram
Figure 2-1. Block diagram.
VCC
RESET
GND
XTAL1
XTAL2
Power
Supervision
POR / BOD &
RESET
Watchdog
Timer
Watchdog
Oscillator
Oscillator
Circuits /
Clock
Generation
PA7..0
PORT A (8)
PB7..0
PORT B (8)
A/D
Converter
Analog
Comparator
EEPROM
Internal
Bandgap reference
SPI
JTAG/OCD
CPU
TWI
FLASH
SRAM
8bit T/C 0
16bit T/C 1
8bit T/C 2
16bit T/C 3*
USART 0
16bit T/C 1
USART 1
PORT C (8)
PORT D (8)
TOSC2/PC7 TOSC1/PC6
PC5..0
PD7..0
* Only available in ATmega1284/1284P
The AVR core combines a rich instruction set with 32 general purpose working registers. All the 32 registers are
directly connected to the Arithmetic Logic Unit (ALU), allowing two independent registers to be accessed in one
single instruction executed in one clock cycle. The resulting architecture is more code efficient while achieving
throughputs up to ten times faster than conventional CISC microcontrollers.
The Atmel ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P provide the following features:
16/32/64/128Kbytes of In-System Programmable Flash with Read-While-Write capabilities, 512/1K/2K/4Kbytes
EEPROM, 1/2/4/16Kbytes SRAM, 32 general purpose I/O lines, 32 general purpose working registers, Real
Time Counter (RTC), three (four for ATmega1284/1284P) flexible Timer/Counters with compare modes and
PWM, 2 USARTs, a byte oriented two-wire Serial Interface, a 8-channel, 10-bit ADC with optional differential
input stage with programmable gain, programmable Watchdog Timer with Internal Oscillator, an SPI serial port,
IEEE std. 1149.1 compliant JTAG test interface, also used for accessing the On-chip Debug system and
programming and six 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 continues to run, allowing the user to maintain a
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timer base while the rest of the device is sleeping. The ADC Noise Reduction mode stops the CPU and all I/O
modules except Asynchronous Timer and ADC, to minimize switching noise during ADC conversions. In
Standby mode, the Crystal/Resonator Oscillator is running while the rest of the device is sleeping. This allows
very fast start-up combined with low power consumption. In Extended Standby mode, both the main Oscillator
and the Asynchronous Timer continue to run.
Atmel offers the QTouch® library for embedding capacitive touch buttons, sliders and wheels functionality into
AVR microcontrollers. The patented charge-transfer signal acquisition offers robust sensing and includes fully
debounced reporting of touch keys and includes Adjacent Key Suppression® (AKS) technology for
unambiguous detection of key events. The easy-to-use QTouch Suite toolchain allows you to explore, develop
and debug your own touch applications.
The device is manufactured using Atmel’s high-density nonvolatile memory technology. The On-chip ISP Flash
allows the program memory to be reprogrammed in-system through an SPI serial interface, by a conventional
nonvolatile 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 ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P is a powerful
microcontroller that provides a highly flexible and cost effective solution to many embedded control applications.
The ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P 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 ATmega164A, ATmega164PA, ATmega324A, ATmega324PA,
ATmega644A, ATmega644PA, ATmega1284 and ATmega1284P
Table 2-1.
Differences between ATmega164A, ATmega164PA, ATmega324A, ATmega324PA, ATmega644A,
ATmega644PA, ATmega1284 and ATmega1284P.
Device
Flash
EEPROM
RAM
Units
ATmega164A
16K
512
1K
ATmega164PA
16K
512
1K
ATmega324A
32K
1K
2K
ATmega324PA
32K
1K
2K
bytes
ATmega644A
64K
2K
4K
ATmega644PA
64K
2K
4K
ATmega1284
128K
4K
16K
ATmega1284P
128K
4K
16K
2.3 Pin Descriptions11
2.3.1 VC
Digital supply voltage.
2.3.2 GND
Ground.
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2.3.3
Port A (PA7:PA0)
Port A serves as analog inputs to the Analog-to-digital Converter.
Port A also serves as 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 Atmel
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P as listed on page 79.
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 also serves the functions of various special features of the
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P as listed on page 80.
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 the JTAG interface, along with special features of the Atmel
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P as listed on page 83.
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
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P as listed on page 86.
2.3.7
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 ”” on page 325. Shorter pulses are not guaranteed to
generate a reset.
2.3.8 XTAL1
Input to the inverting Oscillator amplifier and input to the internal clock operating circuit.
2.3.9 XTAL2
Output from the inverting Oscillator amplifier.
2.3.10 AVCC
AVCC is the supply voltage pin for Port A and the Analog-to-digital 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.
2.3.11 AREF
This is the analog reference pin for the Analog-to-digital Converter.
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3. Resources
A comprehensive set of development tools, application notes and datasheets are available for download on
http://www.atmel.com/avr.
4. About code examples
This documentation contains simple code examples that briefly show how to use various parts of the device. 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.
The code examples assume that the part specific header file is included before compilation. 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".
Note: 1.
5. 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.
6. Capacitive touch sensing
The Atmel QTouch Library provides a simple to use solution to realize touch sensitive interfaces on most Atmel
AVR microcontrollers. The QTouch Library includes support for the QTouch and QMatrix acquisition methods.
Touch sensing can be added to any application by linking the appropriate Atmel QTouch Library for the AVR
Microcontroller. This is done by using a simple set of APIs to define the touch channels and sensors, and then
calling the touch sensing API’s to retrieve the channel information and determine the touch sensor states.
The QTouch Library is FREE and downloadable from the Atmel website at the following location:
www.atmel.com/qtouchlibrary. For implementation details and other information, refer to the Atmel QTouch
Library User Guide - also available for download from the Atmel website.
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7. AVR CPU Core
7.1 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.
Figure 7-1. Block diagram of the AVR architecture.
Flash
Program
Memory
Instruction
Register
Instruction
Decoder
Control Lines
Program
Counter
Data Bus 8-bit
Status
and Control
32 x 8
General
Purpose
Registrers
ALU
Interrupt
Unit
SPI
Unit
Watchdog
Timer
Analog
Comparator
Data
SRAM
EEPROM
I/O Module1
I/O Module 2
I/O Module n
I/O Lines
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
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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 ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P has
Extended I/O space from 0x60 - 0xFF in SRAM where only the ST/STS/STD and LD/LDS/LDD instructions can
be used.
7.2 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.
7.3 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.
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7.3.1 SREG – Status Register
The AVR Status Register – SREG – is defined as:
Bit
0x3F (0x5F)
Read/Write
Initial Value
7
I
R/W
0
6
T
R/W
0
5
H
R/W
0
4
S
R/W
0
3
V
R/W
0
2
N
R/W
0
1
Z
R/W
0
0
C
R/W
0
SREG
• 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 arithmetic. See the “Instruction Set
Description” for detailed information.
• Bit 2 – N: Negative Flag
The Negative Flag N indicates a negative result in an arithmetic or logic operation. See the “Instruction Set
Description” for detailed information.
• Bit 1 – Z: Zero Flag
The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction Set Description”
for detailed information.
• Bit 0 – C: Carry Flag
The Carry Flag C indicates a carry in an arithmetic or logic operation. See the “Instruction Set Description” for
detailed information.
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7.4 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 7-2 shows the structure of the 32 general purpose working registers in the CPU.
Figure 7-2. AVR CPU General Purpose Working Registers.
General
Purpose
Working
Registers
70
R0
R1
R2
R13
R14
R15
R16
R17
R26
R27
R28
R29
R30
R31
Addr.
0x00
0x01
0x02
0x0D
0x0E
0x0F
0x10
0x11
0x1A
0x1B
0x1C
0x1D
0x1E
0x1F
X-register Low Byte
X-register High Byte
Y-register Low Byte
Y-register High Byte
Z-register Low Byte
Z-register High Byte
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 7-2, 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.
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7.4.1
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 7-3.
Figure 7-3.
X-register
The X-, Y-, and Z-registers.
15
7
R27 (0x1B)
XH
07
R26 (0x1A)
XL
0
0
Y-register
15
7
R29 (0x1D)
YH
07
R28 (0x1C)
YL
0
0
Z-register
15
7
R31 (0x1F)
ZH
0
7
R30 (0x1E)
ZL
0
0
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).
7.5 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. Note that the Stack is implemented as growing from higher to lower
memory locations. The Stack Pointer Register always points to the top of the Stack. The Stack Pointer points to
the data SRAM Stack area where the Subroutine and Interrupt Stacks are located. A Stack PUSH command will
decrease the Stack Pointer.
The Stack in the data SRAM must be defined by the program before any subroutine calls are executed or
interrupts are enabled. Initial Stack Pointer value equals the last address of the internal SRAM and the Stack
Pointer must be set to point above start of the SRAM, see Figure 8-2 on page 21.
See Table 7-1 for Stack Pointer details.
Table 7-1. Stack Pointer instructions.
Instruction Stack pointer
Description
PUSH
Decremented by 1 Data is pushed onto the stack
CALL
ICALL
RCALL
Decremented by 2 Return address is pushed onto the stack with a subroutine call or
interrupt
POP
Incremented by 1 Data is popped from the stack
RET
RETI
Incremented by 2 Return address is popped from the stack with return from
subroutine or return from interrupt
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, see Table 7-2 on page 15. 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.
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7.5.1 SPH and SPL – Stack Pointer High and Stack pointer Low
Bit
0x3E (0x5E)
0x3D (0x5D)
Read/Write
Initial Value
15
SP7
7
R
R/W
0
1
14
SP6
6
R
R/W
0
1
13
SP5
5
R
R/W
0
1
12
SP12
SP4
4
R/W
R/W
0/0(1)
1
11
SP11
SP3
3
R/W
R/W
0/1(1)
1
10
SP10
SP2
2
R/W
R/W
1/0(1)
1
9
SP9
SP1
1
R/W
R/W
0
1
8
SP8
SP0
0
R/W
R/W
0
1
SPH
SPL
Note: 1. Initial values respectively for the ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P.
Table 7-2. Stack Pointer size
Device
ATmega164A/ATmega164PA
ATmega324A/ATmega324PA
ATmega644A/ATmega644PA
ATmega1284/ATmega1284P
Stack Pointer size
SP[10:0]
SP[11:0]
SP[12:0]
SP[13:0]
7.5.2 RAMPZ – Extended Z-pointer Register for ELPM/SPM(1)
Bit
0x3B (0x5B)
Read/Write
Initial Value
7
RAMPZ7
R/W
0
6
RAMPZ6
R/W
0
5
RAMPZ5
R/W
0
4
RAMPZ4
R/W
0
3
RAMPZ3
R/W
0
2
RAMPZ2
R/W
0
1
RAMPZ1
R/W
0
0
RAMPZ0
R/W
0
RAMPZ
For ELPM/SPM instructions, the Z-pointer is a concatenation of RAMPZ, ZH, and ZL, as shown in Figure 7-4 on
page 15. Note that LPM is not affected by the RAMPZ setting.
Figure 7-4. The Z-pointer used by ELPM and SPM.
Bit (Individually)
Bit (Z-pointer)
70
RAMPZ
23 16
7
ZH
15
0
8
70
ZL
70
The actual number of bits is implementation dependent. Unused bits in an implementation will always read as
zero. For compatibility with future devices, be sure to write these bits to zero.
Note: 1. RAMPZ is only valid for ATmega1284/ATmega1284P.
7.6 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 7-5 on page 16 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.
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Figure 7-5.
The Parallel Instruction Fetches and Instruction Executions.
T1 T2
T3
T4
clkCPU
1st Instruction Fetch
1st Instruction Execute
2nd Instruction Fetch
2nd Instruction Execute
3rd Instruction Fetch
3rd Instruction Execute
4th Instruction Fetch
Figure 7-6 shows the internal timing concept for the Register File. In a single clock cycle an ALU operation using
two register operands is executed, and the result is stored back to the destination register.
Figure 7-6. Single Cycle ALU operation.
T1
T2 T3
T4
clkCPU
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back
7.7 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. 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 287 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 61. The list also determines the priority levels of the
different interrupts. The lower the address the higher is the priority level. RESET has the highest priority, and
next is INT0 – the External Interrupt Request 0. The Interrupt Vectors can be moved to the start of the Boot
Flash section by setting the IVSEL bit in the MCU Control Register (MCUCR). Refer to ”Interrupts” on page 61
for more information. The Reset Vector can also be moved to the start of the Boot Flash section by
programming the BOOTRST Fuse, see ”Memory programming” on page 287.
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
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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
value
cli
sequence
sbi EECR, EEMPE
EEPROM write
sbi EECR, EEPE
out SREG, r16
SREG value (I-bit)
; store SREG
; disable interrupts during timed
; start
; restore
C Code Example
char cSREG;
cSREG = SREG;
SREG value */
/* disable interrupts during timed sequence */
__disable_interrupt();
EECR |= (1<<EEMPE); /* start EEPROM write */
EECR |= (1<<EEPE);
SREG = cSREG; /* restore SREG value (I-bit) */
/* store
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
sei ; set Global Interrupt Enable
sleep
; enter sleep, waiting for interrupt
; note: will enter sleep before any pending
; interrupt(s)
C Code Example
__enable_interrupt(); /* set Global Interrupt Enable */
__sleep(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */
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7.7.1
Interrupt response time
The interrupt execution response for all the enabled AVR interrupts is four clock cycles minimum. After four
clock cycles the program vector address for the actual interrupt handling routine is executed. During these four
clock cycle period, the Program Counter is pushed onto the Stack. The vector is normally a jump to the interrupt
routine, and this jump takes three clock cycles. If an interrupt occurs during execution of a multi-cycle
instruction, this instruction is completed before the interrupt is served. If an interrupt occurs when the MCU is in
sleep mode, the interrupt execution response time is increased by four clock cycles. This increase comes in
addition to the start-up time from the selected sleep mode.
A return from an interrupt handling routine takes four clock cycles. During these four clock cycles, the Program
Counter (three bytes) is popped back from the Stack, the Stack Pointer is incremented by two, and the I-bit in
SREG is set.
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8. AVR memories
8.1 Overview
This section describes the different memories in the Atmel
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P. The AVR architecture has two main memory
spaces, the Data Memory and the Program Memory space. In addition, the
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P features an EEPROM Memory for data storage.
All three memory spaces are linear and regular.
8.2 In-System Reprogrammable Flash Program Memory
The ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P contains 16/32/64/128Kbytes On-chip In-
System Reprogrammable Flash memory for program storage. Since all AVR instructions are 16 or 32 bits wide,
the Flash is organized as 32/64 x 16. For software security, the Flash Program memory space is divided into
two sections, Boot Program section and Application Program section.
The Flash memory has an endurance of at least 10,000 write/erase cycles. The
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P Program Counter (PC) is 15/16 bits wide, thus
addressing the 32/64K program memory locations. The operation of Boot Program section and associated Boot
Lock bits for software protection are described in detail in ”Memory programming” on page 287. ”Memory
programming” on page 287 contains a detailed description on Flash data serial downloading using the SPI pins
or the JTAG interface.
Constant tables can be allocated within the entire program memory address space (see the LPM – Load
Program Memory instruction description.
Timing diagrams for instruction fetch and execution are presented in ”Instruction Execution Timing” on page 15.
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Figure 8-1. Program memory map.
Program Memory
0x0000
Application Flash Section
Boot Flash Section
0x1FFF/0x3FFF/0x7FFF/0xFFFF
8.3 SRAM data memory
Figure 8-2 shows how the ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P SRAM Memory is
organized.
The ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P is a complex microcontroller with more
peripheral units than can be supported within the 64 location reserved in the Opcode for the IN and OUT
instructions. For the Extended I/O space from $060 - $FF in SRAM, only the ST/STS/STD and LD/LDS/LDD
instructions can be used.
The first 4,352 Data Memory locations address both the Register File, the I/O Memory, Extended I/O Memory,
and the internal data SRAM. The first 32 locations address the Register file, the next 64 location the standard
I/O Memory, then 160 locations of Extended I/O memory and the next 4,096 locations address the internal data
SRAM.
The five different addressing modes for the data memory cover: Direct, Indirect with Displacement, Indirect,
Indirect with Pre-decrement, and Indirect with Post-increment. In the Register file, registers R26 to R31 feature
the indirect addressing pointer registers.
The direct addressing reaches the entire data space.
The Indirect with Displacement mode reaches 63 address locations from the base address given by the Y- or Z-
register.
When using register indirect addressing modes with automatic pre-decrement and post-increment, the address
registers X, Y, and Z are decremented or incremented.
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The 32 general purpose working registers, 64 I/O registers, 160 Extended I/O Registers and
the 1024/2048/4096 bytes of internal data SRAM in the Atmel
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P are all accessible through all these addressing
modes. The Register File is described in ”General Purpose Register File” on page 13.
Figure 8-2.
Data Memory Map for ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P.
Data Memory
32 Registers
64 I/O Registers
160 Ext I/O Reg.
0x0000 - 0x001F
0x0020 - 0x005F
0x0060 - 0x00FF
0x0100
Internal SRAM
(1024/2048/4096/16384x 8)
0x04FF/0x08FF/0x10FF /0x40FF
8.3.1
Data memory access times
This section describes the general access timing concepts for internal memory access. The internal data SRAM
access is performed in two clkCPU cycles as described in Figure 8-3.
Figure 8-3.
On-chip data SRAM access cycles.
T1
T2
T3
clk
CPU
Address
Data
WR
Data
RD
Compute Address
Address valid
Memory Access Instruction
Next Instruction
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8.4 EEPROM data memory
The ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P contains 512/1K/2K/4Kbytes of data
EEPROM memory. It is organized as a separate data space, in which single bytes can be read and written. The
EEPROM has an endurance of at least 100,000 write/erase cycles. The access between the EEPROM and the
CPU is described in the following, specifying the EEPROM Address Registers, the EEPROM Data Register, and
the EEPROM Control Register.
For a detailed description of SPI, JTAG and Parallel data downloading to the EEPROM, see page 291, page
301 and page 306 respectively.
8.4.1
EEPROM Read/Write Access
The EEPROM Access Registers are accessible in the I/O space. See ”Register Description” on page 24 for
details.
The write access time for the EEPROM is given in Table 8-2 on page 26. A self-timing function, however, lets
the user software detect when the next byte can be written. If the user code contains instructions that write the
EEPROM, some precautions must be taken. In heavily filtered power supplies, VCC is likely to rise or fall slowly
on power-up/down. This causes the device for some period of time to run at a voltage lower than specified as
minimum for the clock frequency used. See Section “8.4.2” on page 22 for details on how to avoid problems in
these situations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed. Refer to the
description of the EEPROM Control Register for details on this.
When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is executed.
When the EEPROM is written, the CPU is halted for two clock cycles before the next instruction is executed.
8.4.2
Preventing EEPROM corruption
During periods of low VCC, the EEPROM data can be corrupted because the supply voltage is too low for the
CPU and the EEPROM to operate properly. These issues are the same as for board level systems using
EEPROM, and the same design solutions should be applied.
An EEPROM data corruption can be caused by two situations when the voltage is too low. First, a regular write
sequence to the EEPROM requires a minimum voltage to operate correctly. Secondly, the CPU itself can
execute instructions incorrectly, if the supply voltage is too low.
EEPROM data corruption can easily be avoided by following this design recommendation:
Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This can be done by
enabling the internal Brown-out Detector (BOD). If the detection level of the internal BOD does not match the
needed detection level, an external low VCC reset Protection circuit can be used. If a reset occurs while a write
operation is in progress, the write operation will be completed provided that the power supply voltage is
sufficient.
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8.5 I/O memory
The I/O space definition of the Atmel
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P is shown in ”Register summary” on page 628.
All ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P I/Os and peripherals are placed in the I/O
space. All I/O locations may be accessed by the LD/LDS/LDD and ST/STS/STD instructions, transferring data
between the 32 general purpose working registers and the I/O space. I/O Registers within the address range
0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these registers, the value of single
bits can be checked by using the SBIS and SBIC instructions. Refer to the instruction set section for more
details. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used.
When addressing I/O Registers as data space using LD and ST instructions, 0x20 must be added to these
addresses. The ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P is a complex microcontroller with
more peripheral units than can be supported within the 64 location reserved in Opcode for the IN and OUT
instructions. For the Extended I/O space from 0x60 - 0xFF in SRAM, only the ST/STS/STD and LD/LDS/LDD
instructions can be used.
For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
Some of the Status Flags are cleared by writing a logical one to them. Note that, unlike most other 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.
The I/O and peripherals control registers are explained in later sections.
The ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P contains three General Purpose I/O
Registers, see ”Register Description” on page 24. These registers can be used for storing any information, and
they are particularly useful for storing global variables and Status Flags. General Purpose I/O Registers within
the address range 0x00 - 0x1F are directly bit-accessible using the SBI, CBI, SBIS, and SBIC instructions.
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8.6 Register Description
8.6.1 EEARH and EEARL – The EEPROM Address Register
Bit
0x22 (0x42)
0x21 (0x41)
Read/Write
Initial Value
15
EEAR7
7
R
R/W
0
X
14
EEAR6
6
R
R/W
0
X
13
EEAR5
5
R
R/W
0
X
12
EEAR4
4
R
R/W
0
X
11
EEAR11
EEAR3
3
R/W
R/W
X
X
10
EEAR10
EEAR2
2
R/W
R/W
X
X
9
EEAR9
EEAR1
1
R/W
R/W
X
X
8
EEAR8
EEAR0
0
R/W
R/W
X
X
EEARH
EEARL
• Bits 15:12 – Reserved
These bits are reserved bits in the Atmel
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P and will always read as zero.
• Bits 11:0 – EEAR8:0: EEPROM Address
The EEPROM Address Registers – EEARH and EEARL specify the EEPROM address in the
512/1K/2K/4Kbytes EEPROM space. The EEPROM data bytes are addressed linearly between 0 and
511/1023/2047/4096. The initial value of EEAR is undefined. A proper value must be written before the
EEPROM may be accessed.
8.6.2 EEDR – The EEPROM Data Register
Bit
0x20 (0x40)
Read/Write
Initial Value
7
MSB
R/W
0
6
R/W
0
5
R/W
0
4
R/W
0
3
R/W
0
2
R/W
0
1
R/W
0
0
LSB
R/W
0
EEDR
• Bits 7:0 – EEDR7:0: EEPROM Data
For the EEPROM write operation, the EEDR Register contains the data to be written to the EEPROM in the
address given by the EEAR Register. For the EEPROM read operation, the EEDR contains the data read out
from the EEPROM at the address given by EEAR.
8.6.3 EECR – The EEPROM Control Register
Bit 7 6 5 4
0x1F (0x3F)
– EEPM1 EEPM0
Read/Write
R
R
R/W
R/W
Initial Value 0 0 X X
3
EERIE
R/W
0
2
EEMPE
R/W
0
1
EEPE
R/W
X
0
EERE
R/W
0
EECR
• Bits 7:6 – Reserved
These bits are reserved bits in the ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P and will always
read as zero.
• Bits 5:4 – EEPM1 and EEPM0: EEPROM Programming Mode Bits
The EEPROM Programming mode bit setting defines which programming action that will be triggered when
writing EEPE. It is possible to program data in one atomic operation (erase the old value and program the new
value) or to split the Erase and Write operations in two different operations. The Programming times for the
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different modes are shown in Table 8-1 on page 25. While EEPE is set, any write to EEPMn will be ignored.
During reset, the EEPMn bits will be reset to 0b00 unless the EEPROM is busy programming.
Table 8-1.
EEPM1
0
0
1
1
EEPROM Mode Bits.
EEPM0
Programming time
0 3.4ms
1 1.8ms
0 1.8ms
1–
Operation
Erase and Write in one operation (Atomic Operation)
Erase Only
Write Only
Reserved for future use
• Bit 3 – EERIE: EEPROM Ready Interrupt Enable
Writing EERIE to one enables the EEPROM Ready Interrupt if the I bit in SREG is set. Writing EERIE to zero
disables the interrupt. The EEPROM Ready interrupt generates a constant interrupt when EEPE is cleared.
• Bit 2 – EEMPE: EEPROM Master Programming Enable
The EEMPE bit determines whether setting EEPE to one causes the EEPROM to be written. When EEMPE is
set, setting EEPE within four clock cycles will write data to the EEPROM at the selected address If EEMPE is
zero, setting EEPE will have no effect. When EEMPE has been written to one by software, hardware clears the
bit to zero after four clock cycles. See the description of the EEPE bit for an EEPROM write procedure.
• Bit 1 – EEPE: EEPROM Programming Enable
The EEPROM Write Enable Signal EEPE is the write strobe to the EEPROM. When address and data are
correctly set up, the EEPE bit must be written to one to write the value into the EEPROM. The EEMPE bit must
be written to one before a logical one is written to EEPE, otherwise no EEPROM write takes place. The
following procedure should be followed when writing the EEPROM (the order of steps 3 and 4 is not essential):
1. Wait until EEPE becomes zero.
2. Wait until SPMEN in SPMCSR becomes zero.
3. Write new EEPROM address to EEAR (optional).
4. Write new EEPROM data to EEDR (optional).
5. Write a logical one to the EEMPE bit while writing a zero to EEPE in EECR.
6. Within four clock cycles after setting EEMPE, write a logical one to EEPE.
The EEPROM can not be programmed during a CPU write to the Flash memory. The software must check that
the Flash programming is completed before initiating a new EEPROM write. Step 2 is only relevant if the
software contains a Boot Loader allowing the CPU to program the Flash. If the Flash is never being updated by
the CPU, step 2 can be omitted. See ”Memory programming” on page 287 for details about Boot programming.
Caution: An interrupt between step 5 and step 6 will make the write cycle fail, since the EEPROM Master Write
Enable will time-out. If an interrupt routine accessing the EEPROM is interrupting another EEPROM access, the
EEAR or EEDR Register will be modified, causing the interrupted EEPROM access to fail. It is recommended to
have the Global Interrupt Flag cleared during all the steps to avoid these problems.
When the write access time has elapsed, the EEPE bit is cleared by hardware. The user software can poll this
bit and wait for a zero before writing the next byte. When EEPE has been set, the CPU is halted for two cycles
before the next instruction is executed.
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• Bit 0 – EERE: EEPROM Read Enable
The EEPROM Read Enable Signal EERE is the read strobe to the EEPROM. When the correct address is set
up in the EEAR Register, the EERE bit must be written to a logic one to trigger the EEPROM read. The
EEPROM read access takes one instruction, and the requested data is available immediately. When the
EEPROM is read, the CPU is halted for four cycles before the next instruction is executed.
The user should poll the EEPE bit before starting the read operation. If a write operation is in progress, it is
neither possible to read the EEPROM, nor to change the EEAR Register.
The calibrated Oscillator is used to time the EEPROM accesses. Table 8-2 on page 26 lists the typical
programming time for EEPROM access from the CPU.
Table 8-2. EEPROM programming time.
Symbol
Number of calibrated RC oscillator cycles
EEPROM write
(from CPU)
26,368
Typical programming time
3.3ms
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The following code examples show one assembly and one C function for writing to the EEPROM. The examples
assume that interrupts are controlled (e.g. by disabling interrupts globally) so that no interrupts will occur during
execution of these functions. The examples also assume that no Flash Boot Loader is present in the software. If
such code is present, the EEPROM write function must also wait for any ongoing SPM command to finish.
Assembly Code Example (1)
EEPROM_write:
; Wait for completion of previous write
sbic
EECR,EEPE
rjmp
EEPROM_write
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Write data (r16) to Data Register
out EEDR,r16
; Write logical one to EEMPE
sbi EECR,EEMPE
; Start eeprom write by setting EEPE
sbi EECR,EEPE
ret
C Code Example (1)
void EEPROM_write(unsigned int uiAddress, unsigned char ucData)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set up address and Data Registers */
EEAR = uiAddress;
EEDR = ucData;
/* Write logical one to EEMPE */
EECR |= (1<<EEMPE);
/* Start eeprom write by setting EEPE */
EECR |= (1<<EEPE);
}
Note: 1. See “About code examples” on page 9.
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The next code examples show assembly and C functions for reading the EEPROM. The examples assume that
interrupts are controlled so that no interrupts will occur during execution of these functions.
Assembly Code Example (1)
EEPROM_read:
; Wait for completion of previous write
sbic
EECR,EEPE
rjmp
EEPROM_read
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Start eeprom read by writing EERE
sbi EECR,EERE
; Read data from Data Register
in r16,EEDR
ret
C Code Example (1)
unsigned char EEPROM_read(unsigned int uiAddress)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set up address register */
EEAR = uiAddress;
/* Start eeprom read by writing EERE */
EECR |= (1<<EERE);
/* Return data from Data Register */
return EEDR;
}
Note: 1. See “About code examples” on page 9.
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8.6.4 GPIOR2 – General Purpose I/O Register 2
Bit
0x2B (0x4B)
Read/Write
Initial Value
7
MSB
R/W
0
6
R/W
0
5
R/W
0
4
R/W
0
3
R/W
0
2
R/W
0
1
R/W
0
0
LSB
R/W
0
GPIOR2
8.6.5 GPIOR1 – General Purpose I/O Register 1
Bit
0x2A (0x4A)
Read/Write
Initial Value
7
MSB
R/W
0
6
R/W
0
5
R/W
0
4
R/W
0
3
R/W
0
2
R/W
0
1
R/W
0
0
LSB
R/W
0
GPIOR1
8.6.6 GPIOR0 – General Purpose I/O Register 0
Bit
0x1E (0x3E)
Read/Write
Initial Value
7
MSB
R/W
0
6
R/W
0
5
R/W
0
4
R/W
0
3
R/W
0
2
R/W
0
1
R/W
0
0
LSB
R/W
0
GPIOR0
Note:
1. SRWn1 = SRW11 (upper sector) or SRW01 (lower sector), SRWn0 = SRW10 (upper sector) or SRW00 (lower
sector). The ALE pulse in period T4 is only present if the next instruction accesses the RAM (internal or
external).
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9. System clock and clock options
9.1 Clock systems and their distribution
Figure 9-1 presents the principal clock systems in the AVR and their distribution. All of the clocks need not be
active at a given time. In order to reduce power consumption, the clocks to modules not being used can be
halted by using different sleep modes, as described in ”Power management and sleep modes” on page 42. The
clock systems are detailed below.
Figure 9-1.
Clock distribution.
Asynchronous
Timer/Counter
General I/O
Modules
ADC
CPU Core
RAM
Flash and
EEPROM
clkI/O
clkASY
clkADC
AVR Clock
Control Unit
clkCPU
clkFLASH
Reset Logic
Watchdog Timer
Source clock
System Clock
Prescaler
Clock
Multiplexer
Watchdog clock
Watchdog
Oscillator
Timer/Counter
Oscillator
External Clock
Crystal
Oscillator
Low-frequency
Crystal Oscillator
Calibrated RC
Oscillator
9.1.1
CPU Clock – clkCPU
The CPU clock is routed to parts of the system concerned with operation of the AVR core. Examples of such
modules are the General Purpose Register File, the Status Register and the data memory holding the Stack
Pointer. Halting the CPU clock inhibits the core from performing general operations and calculations.
9.1.2
I/O Clock – clkI/O
The I/O clock is used by the majority of the I/O modules, like Timer/Counters, SPI, and USART. The I/O clock is
also used by the External Interrupt module, but note that some external interrupts are detected by asynchronous
logic, allowing such interrupts to be detected even if the I/O clock is halted. Also note that start condition
detection in the USI module is carried out asynchronously when clkI/O is halted, TWI address recognition in all
sleep modes.
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