ATmega48/88/168
Overview........................................................................................................... 132
Timer/Counter Clock Sources........................................................................... 133
Counter Unit...................................................................................................... 133
Output Compare Unit........................................................................................ 134
Compare Match Output Unit............................................................................. 136
Modes of Operation .......................................................................................... 137
Timer/Counter Timing Diagrams....................................................................... 141
8-bit Timer/Counter Register Description ......................................................... 143
Asynchronous operation of the Timer/Counter................................................. 149
Timer/Counter Prescaler................................................................................... 152
Serial Peripheral Interface – SPI..................................................... 153
SS Pin Functionality.......................................................................................... 158
Data Modes ...................................................................................................... 160
USART0 ............................................................................................ 162
Overview........................................................................................................... 162
Clock Generation.............................................................................................. 163
Frame Formats ................................................................................................. 166
USART Initialization.......................................................................................... 167
Data Transmission – The USART Transmitter ................................................. 168
Data Reception – The USART Receiver .......................................................... 171
Asynchronous Data Reception ......................................................................... 175
Multi-processor Communication Mode ............................................................. 179
USART Register Description ............................................................................ 180
Examples of Baud Rate Setting........................................................................ 185
USART in SPI Mode......................................................................... 189
Overview........................................................................................................... 189
Clock Generation.............................................................................................. 189
SPI Data Modes and Timing............................................................................. 190
Frame Formats ................................................................................................. 190
Data Transfer.................................................................................................... 192
USART MSPIM Register Description ............................................................... 194
AVR USART MSPIM vs.
AVR SPI............................................................................................................ 197
2-wire Serial Interface...................................................................... 198
Features............................................................................................................ 198
2-wire Serial Interface Bus Definition................................................................ 198
Data Transfer and Frame Format..................................................................... 199
Multi-master Bus Systems, Arbitration and Synchronization............................ 202
Overview of the TWI Module ............................................................................ 204
TWI Register Description.................................................................................. 206
Using the TWI................................................................................................... 209
Transmission Modes......................................................................................... 213
iii
2545D–AVR–07/04
ATMEL [ ATMEL ]
