ATmega88 SRAM data memory

Figure 10 shows the organization of the ATmega88 SRAM space. The

ATmega88 is a complex microcontroller that supports more peripherals than the reserved 64 I/Os (accessed by IN OUT instructions). For the extended I/O 0x60 - 0xFF, only ST/STS/STD and LD/LDS/LDD instructions can be used. The

first 1280 data memory includes the register file, I/O memory, extended I/O memory, and data SRAM. The first 32 addresses are the register file, followed by the 64 I/O memory, followed by the 160 extended I/O memory. Finally, there is the 1024-byte data SRAM.

The data memory is addressed in five ways: direct addressing, indirect addressing with offset, indirect addressing, indirect addressing with pre-decrement, and indirect addressing with post-increment. Registers R26 to R31 in the register file are pointer registers for indirect addressing.

The direct addressing range can reach the entire data area.

The indirect addressing mode with offset can address 63 addresses near the base address given by registers Y and Z.

In the automatic pre-decrement and post-increment indirect addressing mode, registers X, Y and Z are automatically increased or decreased.

All 32 general registers, 64 I/O registers, 160 extended I/O registers and 1024 bytes of internal data SRAM of ATmega88 can be accessed through all the above addressing modes. For a description of the register file, see P8 "General Register File".

SRAM Data Memory Access Time

This section describes the timing for accessing the internal memory. As shown in Figure 11, the internal data SRAM access time is two clkCPU clocks.