ATMEGA644 datasheet(26/374 Pages) ATMEL

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2593L–AVR–02/07

ATmega644

6.4

I/O Memory

The I/O space definition of the ATmega644 is shown in ”Register Summary” on page 352.

All ATmega644 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 ATmega644 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 reg-

isters 0x00 to 0x1F only.

The I/O and peripherals control registers are explained in later sections.

6.4.1

General Purpose I/O Registers

The ATmega644 contains three General Purpose I/O Registers. These registers can be used for

storing any information, and they are particularly useful for storing global variables and Status

Flags. General Purpose I/O Registers within the address range 0x00 - 0x1F are directly bit-

accessible using the SBI, CBI, SBIS, and SBIC instructions.

6.4.2

GPIOR2 – General Purpose I/O Register 2

6.4.3

GPIOR1 – General Purpose I/O Register 1

Bit

543210

0x2B (0x4B)

MSB

LSB

GPIOR2

Read/Write

R/W

Initial Value

000000

Bit

76543210

0x2A (0x4A)

MSB

LSB

GPIOR1

Read/Write

R/W

Initial Value

00000000

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