ATmega328P datasheet(18/448 Pages) ATMEL

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8161D–AVR–10/09

ATmega48PA/88PA/168PA/328P

7.3

SRAM Data Memory

Figure 7-3 shows how the ATmega48PA/88PA/168PA/328P SRAM Memory is organized.

The ATmega48PA/88PA/168PA/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

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 768/1280/1280/2303 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

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 ATmega48PA/88PA/168PA/328P

are all accessible through all these addressing modes. The Register File is described in ”Gen-

eral Purpose Register File” on page 11.

Figure 7-3.

Data Memory Map

32 Registers

64 I/O Registers

Internal SRAM

(512/1024/1024/2048 x 8)

0x0000 - 0x001F

0x0020 - 0x005F

0x04FF/0x04FF/0x0FF/0x08FF

0x0060 - 0x00FF

Data Memory

160 Ext I/O Reg.

0x0100

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