General Purpose Register File - Atmel ATmega48A Manual

7.4

General Purpose Register File

8271D–AVR–05/11
ATmega48A/PA/88A/PA/168A/PA/328/P
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 7-2 shows the structure of the 32 general purpose working registers in the CPU.
Figure 7-2. AVR CPU General Purpose Working Registers
General
Purpose
Working
Registers
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 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 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.
7 0
R0
R1
R2
...
R13
R14
R15
R16
R17
...
R26
R27
R28
R29
R30
R31
Addr.
0x00
0x01
0x02
0x0D
0x0E
0x0F
0x10
0x11
0x1A X-register Low Byte
0x1B X-register High Byte
0x1C Y-register Low Byte
0x1D Y-register High Byte
0x1E Z-register Low Byte
0x1F Z-register High Byte
12