The I/O memory space contains 64 addresses for CPU peripheral functions such as
control registers, timer/counters, A/D converters and other I/O functions. The I/O mem-
ory can be accessed directly or as the Data Space locations following those of the
register file, $20 - $5F.
The AVR has Harvard architecture – with separate memories and buses for program
and data. The program memory is accessed with a 2-stage pipeline. While one instruc-
tion is being executed, the next instruction is pre-fetched from the program memory.
This concept enables instructions to be executed in every clock cycle. The program
memory is In-System Programmable Flash memory.
With the relative jump and call instructions, the whole 1K address space is directly
accessed. Most AVR instructions have a single 16-bit word format. Every program
memory address contains a 16- or 32-bit instruction.
During interrupts and subroutine calls, the return address Program Counter (PC) is
stored on the stack. The stack is effectively allocated in the general data SRAM, and
consequently the stack size is only limited by the total SRAM size and the usage of the
SRAM. All user programs must initialize the SP in the reset routine (before subroutines
or interrupts are executed). The 8-bit stack pointer (SP) is read/write accessible in the
I/O space.
The 128 bytes data SRAM + register file and I/O registers can be easily accessed
through the five different addressing modes supported in the AVR architecture.
The memory spaces in the AVR architecture are all linear and regular memory maps.
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AT90S2313
0839G–08/01
ATMEL [ ATMEL CORPORATION ]
