Atmel ATmega48A

iv
8271D–AVR–05/11
ATmega48A/PA/88A/PA/168A/PA/328/P
18 8-bit Timer/Counter2 with PWM and Asynchronous Operation ...... 146
18.1Features ..............................................................................................................146
18.2Overview .............................................................................................................146
18.3Timer/Counter Clock Sources .............................................................................147
18.4Counter Unit ........................................................................................................147
18.5Output Compare Unit ..........................................................................................148
18.6Compare Match Output Unit ................................................................................150
18.7Modes of Operation .............................................................................................151
18.8Timer/Counter Timing Diagrams .........................................................................155
18.9Asynchronous Operation of Timer/Counter2 .......................................................157
18.10Timer/Counter Prescaler ...................................................................................158
18.11Register Description ..........................................................................................160
19 SPI – Serial Peripheral Interface ......................................................... 168
19.1Features ..............................................................................................................168
19.2Overview .............................................................................................................168
19.3SS
Pin Functionality ............................................................................................173
19.4Data Modes .........................................................................................................173
19.5Register Description ............................................................................................175
20 USART0 ................................................................................................. 178
20.1Features ..............................................................................................................178
20.2Overview .............................................................................................................178
20.3Clock Generation .................................................................................................179
20.4Frame Formats ....................................................................................................182
20.5USART Initialization ............................................................................................184
20.6Data Transmission – The USART Transmitter ....................................................185
20.7Data Reception – The USART Receiver .............................................................188
20.8Asynchronous Data Reception ............................................................................192
20.9Multi-processor Communication Mode ................................................................195
20.10Examples of Baud Rate Setting ........................................................................196
20.11Register Description ..........................................................................................201
21 USART in SPI Mode ............................................................................. 206
21.1Features ..............................................................................................................206
21.2Overview .............................................................................................................206
21.3Clock Generation .................................................................................................206
21.4SPI Data Modes and Timing ...............................................................................207