ATmega1284P datasheet(23/468 Pages) ATMEL

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8152G–AVR–11/09

ATmega164PA/324PA/644PA/1284P

7.5

I/O Memory

The I/O space definition of the ATmega164PA/324PA/644PA/1284P is shown in ”Register Sum-

mary” on page 442.

All ATmega164PA/324PA/644PA/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

ATmega164PA/324PA/644PA/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 instruc-

tions. For the Extended I/O space from 0x60 - 0xFF in SRAM, only the ST/STS/STD and

LD/LDS/LDD instructions can be used.

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.

The ATmega164PA/324PA/644PA/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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