Datasheet

ATmega48/88/168 Automotive [DATASHEET]

7530K–AVR–07/14

Figure 5-2. Program Memory Map, ATmega88 and ATmega168

5.2 SRAM Data Memory

Figure 5-3 shows how the Atmel

ATmega48/88/168 SRAM Memory is organized.

The Atmel ATmega48/88/168 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 instructions. 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 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 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, 160 extended I/O registers, and the 512/1024/1024 bytes of

internal data SRAM in the Atmel ATmega48/88/168 are all accessible through all these addressing modes. The register file

is described in Section 4.5 “General Purpose Register File” on page 11.

Figure 5-3. Data Memory Map

0x0000

0x3FFF/0x7FFF

Boot Flash Section

Program Memory

Application Flash Section

32 Registers

Data Memory

0x0000 - 0x001F

0x0020 - 0x005F

0x0060 - 0x00FF

0x0100

0x02FF/0x04FF/0x08FF

64 I/O Registers

160 Ext I/O Registers

Internal SRAM

(512/1024/1024 x 8)