ATmega1284P datasheet(20/380 Pages) ATMEL

20 / 380 page

8059D–AVR–11/09

ATmega1284P

6.5

I/O Memory

The I/O space definition of the ATmega1284P is shown in ”Register Summary” on page 360.

All ATmega1284P 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 ATmega1284P is a com-

plex 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.

The ATmega1284P contains three General Purpose I/O Registers, see ”Register Description”

on page 21. 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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