Datasheet

i
2545F–AVR–06/05
Table of Contents
Features ..................................................................................................... 1
1 Pin Configurations ................................................................................... 2
1.1 Disclaimer .................................................................................................................3
2 Overview ................................................................................................... 3
2.1 Block Diagram ..........................................................................................................3
2.2 Comparison Between ATmega48, ATmega88, and ATmega168 ............................4
2.3 Pin Descriptions .......................................................................................................5
3 Resources ................................................................................................. 6
4 About Code Examples ............................................................................. 6
5 AVR CPU Core .......................................................................................... 7
5.1 Introduction ...............................................................................................................7
5.2 Architectural Overview .............................................................................................7
5.3 ALU – Arithmetic Logic Unit .....................................................................................8
5.4 Status Register .........................................................................................................9
5.5 General Purpose Register File ...............................................................................10
5.6 Stack Pointer ..........................................................................................................11
5.7 Instruction Execution Timing ..................................................................................12
5.8 Reset and Interrupt Handling .................................................................................12
6 AVR ATmega48/88/168 Memories ........................................................ 15
6.1 In-System Reprogrammable Flash Program Memory ............................................15
6.2 SRAM Data Memory ..............................................................................................17
6.3 EEPROM Data Memory .........................................................................................18
6.4 I/O Memory .............................................................................................................24
7 System Clock and Clock Options ......................................................... 25
7.1 Clock Systems and their Distribution ......................................................................25
7.2 Clock Sources ........................................................................................................26
7.3 Low Power Crystal Oscillator ..................................................................................27
7.4 Full Swing Crystal Oscillator ...................................................................................29
7.5 Low Frequency Crystal Oscillator ...........................................................................31
7.6 Calibrated Internal RC Oscillator ............................................................................31
7.7 128 kHz Internal Oscillator .....................................................................................33
7.8 External Clock ........................................................................................................33