Sram Data Memory - Atmel ATmega48PV Manual

5.3

SRAM Data Memory

8025I–AVR–02/09
Figure 5-3 shows how the ATmega48P/88P/168P/328P SRAM Memory is organized.
The ATmega48P/88P/168P/328P is a complex microcontroller with more peripheral units than
can be supported within the 64 locations reserved in the Opcode for the IN and OUT instruc-
tions. For the Extended I/O space from 0x60 - 0xFF in SRAM, only the ST/STS/STD and
LD/LDS/LDD instructions can be used.
The lower 768/1280/1280/2303 data memory locations address both the Register File, the I/O
memory, Extended I/O memory, and the internal data SRAM. The first 32 locations address the
Register File, the next 64 location the standard I/O memory, then 160 locations of Extended I/O
memory, and the next 512/1024/1024/2048 locations address the internal data SRAM.
The five different addressing modes for the data memory cover: Direct, Indirect with Displace-
ment, 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-incre-
ment, the address registers X, Y, and Z are decremented or incremented.
The 32 general purpose working registers, 64 I/O Registers, 160 Extended I/O Registers, and
the 512/1024/1024/2048 bytes of internal data SRAM in the ATmega48P/88P/168P/328P are all
accessible through all these addressing modes. The Register File is described in
pose Register File" on page
Figure 5-3. Data Memory Map
Data Memory
64 I/O Registers
160 Ext I/O Reg.
Internal SRAM
(512/1024/1024/2048 x 8)
ATmega48P/88P/168P/328P
11.
0x0000 - 0x001F
32 Registers
0x0020 - 0x005F
0x0060 - 0x00FF
0x0100
0x02FF/0x04FF/0x04FF/0x08FF
"General Pur-
18