ATMEGA8515_14 Datasheet, PDF (11/257 Pages) ATMEL Corporation – High-performance, Low-power AVR

General Purpose
Register File
ATmega8515(L)
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 4 shows the structure of the 32 general purpose working registers in the CPU.
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.
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2512K–AVR–01/10