SRAM Data Memory
Figure 8 shows how the ATmega8 SRAM Memory is organized.
The lower 1120 Data memory locations address the Register File, the I/O Memory, and
the internal data SRAM. The first 96 locations address the Register File and I/O Mem-
ory, and the next 1024 locations address the internal data SRAM.
The five different addressing modes for the Data memory cover: Direct, Indirect with
Displacement, Indirect, Indirect with Pre-decrement, and Indirect with Post-increment. In
the Register File, registers R26 to R31 feature the indirect addressing pointer registers.
The direct addressing reaches the entire data space.
The Indirect with Displacement mode reaches 63 address locations from the base
address given by the Y- or Z-register.
When using register indirect addressing modes with automatic pre-decrement and post-
increment, the address registers X, Y and Z are decremented or incremented.
The 32 general purpose working registers, 64 I/O Registers, and the 1024 bytes of inter-
nal data SRAM in the ATmega8 are all accessible through all these addressing modes.
The Register File is described in “General Purpose Register File” on page 10.
Figure 8. Data Memory Map
Register File
Data Address Space
R0
R1
$0000
$0001
R2
...
$0002
...
R29
R30
R31
$001D
$001E
$001F
I/O Registers
$00
$01
$0020
$0021
$02
...
$0022
...
$3D
$3E
$3F
$005D
$005E
$005F
Internal SRAM
$0060
$0061
...
$045E
$045F
16
ATmega8(L)
2486M–AVR–12/03
ATMEL [ ATMEL ]
