ATMEGA640 datasheet(14/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

•

Two 8-bit output operands and one 16-bit result input

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One 16-bit output operand and one 16-bit result input

Figure 7-2 shows the structure of the 32 general purpose working registers in the CPU.

Figure 7-2.

AVR CPU General Purpose Working Registers

Most of the instructions operating on the Register File have direct access to all registers, and most of them are sin-

gle cycle instructions.

As shown in Figure 7-2, 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 physically 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.

7.5.1

The X-register, Y-register, and Z-register

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

defined as described in Figure 7-3.

Figure 7-3.

The X-, Y-, and Z-registers

In the different addressing modes these address registers have functions as fixed displacement, automatic incre-

ment, and automatic decrement (see the “Instruction Set Summary” on page 404 for details).

Addr.

0x00

0x01

0x02

…

R13

0x0D

General

R14

0x0E

Purpose

R15

0x0F

Working

R16

0x10

Registers

R17

0x11

…

R26

0x1A

X-register Low Byte

R27

0x1B

X-register High Byte

R28

0x1C

Y-register Low Byte

R29

0x1D

Y-register High Byte

R30

0x1E

Z-register Low Byte

R31

0x1F

Z-register High Byte

X-register

R27 (0x1B)

R26 (0x1A)

Y-register

R29 (0x1D)

R28 (0x1C)

Z-register

R31 (0x1F)

R30 (0x1E)

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