ATMEGA128 データシートの表示（PDF） - Atmel Corporation

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ATMEGA128

8-bit Microcontroller with 128K Bytes In-System Programmable Flash

Atmel Corporation 

ATmega128

X-register, Y-register, and Z-

register

Figure 4. AVR CPU General Purpose Working Registers

General

Purpose

Working

Registers

7

0

R0

R1

R2

…

R13

R14

R15

R16

R17

…

R26

R27

R28

R29

R30

R31

Addr.

$00

$01

$02

$0D

$0E

$0F

$10

$11

$1A

$1B

$1C

$1D

$1E

$1F

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 4, 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 phys-

ically 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.

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 described in Figure 5.

Figure 5. The X-, Y-, and Z-registers

15

XH

XL

0

X - register

7

07

0

R27 ($1B)

R26 ($1A)

15

YH

YL

0

Y - register

7

07

0

R29 ($1D)

R28 ($1C)

15

ZH

ZL

0

Z - register

7

07

0

R31 ($1F)

R30 ($1E)

In the different addressing modes these address registers have functions as fixed dis-

placement, automatic increment, and automatic decrement (see the Instruction Set

Reference for details).

13

2467O–AVR–10/06

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