ATmega8A
6.4
General Purpose Register File
The Register File is optimized for the AVR Enhanced RISC instruction set. In order to achieve
the required performance and flexibility, the following input/output schemes are supported by the
Register File:
• One 8-bit output operand and one 8-bit result input.
• Two 8-bit output operands and one 8-bit result input.
• Two 8-bit output operands and one 16-bit result input.
• One 16-bit output operand and one 16-bit result input.
Figure 6-2 shows the structure of the 32 general purpose working registers in the CPU.
Figure 6-2. AVR CPU General Purpose Working Registers
7
0
Addr.
R0
R1
0x00
0x01
0x02
R2
…
R13
R14
R15
R16
R17
…
0x0D
0x0E
0x0F
0x10
0x11
General
Purpose
Working
Registers
R26
R27
R28
R29
R30
R31
0x1A
0x1B
0x1C
0x1D
0x1E
0x1F
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 6-2, 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 imple-
mented 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.
10
8159C–AVR–07/09
ATMEL [ ATMEL ]
