Datasheet

ATmega640/1280/1281/2560/2561

2549K–AVR–01/07

I/O Memory The I/O space definition of the ATmega640/1280/1281/2560/2561 is shown in “Register

Summary” on page 416.

All ATmega640/1280/1281/2560/2561 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

ATmega640/1280/1281/2560/2561 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 - 0x1FF 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.

General Purpose I/O Registers The ATmega640/1280/1281/2560/2561 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. See “Register Description” on page 32.