atmega161-4pi ATMEL Corporation, atmega161-4pi Datasheet - Page 8

• Manufacturer Part Number: atmega161-4pi
• Description: 8-bit Microcontroller With 16k Bytes Of In-system Programmable Flash
• Manufacturer: ATMEL Corporation

In addition to the register operation, the conventional Memory Addressing modes can be
used on the Register File. This is enabled by the fact that the Register File is assigned
the 32 lowermost Data Space addresses ($00 - $1F), allowing them to be accessed as
though they were ordinary memory locations.
The I/O memory space contains 64 addresses for CPU peripheral functions such as
Control Registers, Timer/Counters, and other I/O functions. The I/O memory can be
accessed directly or as the Data Space locations following those of the Register File,
$20 - $5F.
The AVR uses a Harvard architecture concept – with separate memories and buses for
program and data. The Program memory is executed with a two-stage pipeline. While
one instruction 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 Self-programmable Flash memory.
With the jump and call instructions, the whole 8K word 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 (Stack Pointer) in the reset routine
(before subroutines or interrupts are executed). The 16-bit Stack Pointer is read/write
accessible in the I/O space.
The 1K byte data SRAM 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.
ATmega161(L)
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1228D–AVR–02/07