Datasheet

20.2. Overview...................................................................................................................................214
20.3. SS Pin Functionality................................................................................................................. 218
20.4. Data Modes.............................................................................................................................. 218
20.5. Register Description................................................................................................................. 219
21. USART - Universal Synchronous Asynchronous Receiver Transceiver................224
21.1. Features................................................................................................................................... 224
21.2. Overview...................................................................................................................................224
21.3. Block Diagram.......................................................................................................................... 224
21.4. Clock Generation......................................................................................................................225
21.5. Frame Formats.........................................................................................................................228
21.6. USART Initialization..................................................................................................................229
21.7. Data Transmission – The USART Transmitter......................................................................... 230
21.8. Data Reception – The USART Receiver.................................................................................. 232
21.9. Asynchronous Data Reception.................................................................................................235
21.10. Multi-Processor Communication Mode.................................................................................... 238
21.11. Examples of Baud Rate Setting............................................................................................... 239
21.12. Register Description.................................................................................................................242
22. USARTSPI - USART in SPI Mode.........................................................................252
22.1. Features................................................................................................................................... 252
22.2. Overview...................................................................................................................................252
22.3. Clock Generation......................................................................................................................252
22.4. SPI Data Modes and Timing.....................................................................................................253
22.5. Frame Formats.........................................................................................................................253
22.6. Data Transfer............................................................................................................................255
22.7. AVR USART MSPIM vs. AVR SPI............................................................................................256
22.8. Register Description................................................................................................................. 257
23. TWI - 2-wire Serial Interface..................................................................................258
23.1. Features................................................................................................................................... 258
23.2. Two-Wire Serial Interface Bus Definition..................................................................................258
23.3. Data Transfer and Frame Format.............................................................................................259
23.4. Multi-master Bus Systems, Arbitration, and Synchronization...................................................262
23.5. Overview of the TWI Module.................................................................................................... 264
23.6. Using the TWI...........................................................................................................................266
23.7. Transmission Modes................................................................................................................ 269
23.8. Multi-master Systems and Arbitration.......................................................................................287
23.9. Register Description................................................................................................................. 289
24. AC - Analog Comparator....................................................................................... 297
24.1. Overview...................................................................................................................................297
24.2. Analog Comparator Multiplexed Input...................................................................................... 297
24.3. Register Description................................................................................................................. 298
25. ADC - Analog to Digital Converter.........................................................................302
25.1. Features................................................................................................................................... 302
25.2. Overview...................................................................................................................................302
25.3. Starting a Conversion...............................................................................................................304
Atmel ATmega644A [DATASHEET]
Atmel-42716C-ATmega644A_Datasheet_Complete-10/2016
6