ATMEGA8_14 Datasheet, PDF (9/331 Pages) ATMEL Corporation – High-performance, Low-power Atmel

ATmega8(L)
Atmel AVR CPU
Core
Introduction
Architectural
Overview
This section discusses the Atmel^®AVR^® core architecture in general. The main function of the
CPU core is to ensure correct program execution. The CPU must therefore be able to access
memories, perform calculations, control peripherals, and handle interrupts.
Figure 2. Block Diagram of the AVR MCU Architecture
Data Bus 8-bit
Flash
Program
Memory
Instruction
Register
Instruction
Decoder
Control Lines
Program
Counter
Status
and Control
32 x 8
General
Purpose
Registrers
ALU
Interrupt
Unit
SPI
Unit
Watchdog
Timer
Analog
Comparator
Data
SRAM
EEPROM
i/O Module1
i/O Module 2
i/O Module n
I/O Lines
2486AA–AVR–02/2013
In order to maximize performance and parallelism, the AVR uses a Harvard architecture – with
separate memories and buses for program and data. Instructions in the Program memory are
executed with a single level pipelining. While one instruction is being executed, the next instruc-
tion is pre-fetched from the Program memory. This concept enables instructions to be executed
in every clock cycle. The Program memory is In-System Reprogrammable Flash memory.
The fast-access Register File contains 32 × 8-bit general purpose working registers with a single
clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU) operation. In a typ-
ical ALU operation, two operands are output from the Register File, the operation is executed,
and the result is stored back in the Register File – in one clock cycle.
Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data
Space addressing – enabling efficient address calculations. One of the these address pointers
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