22. USART
22.1 Features
• Full Duplex Operation (Independent Serial Receive and Transmit Registers)
• Asynchronous or Synchronous Operation
• Master or Slave Clocked Synchronous Operation
• High Resolution Baud Rate Generator
• Supports Serial Frames with 5, 6, 7, 8, or 9 Data Bits and 1 or 2 Stop Bits
• Odd or Even Parity Generation and Parity Check Supported by Hardware
• Data OverRun Detection
• Framing Error Detection
• Noise Filtering Includes False Start Bit Detection and Digital Low Pass Filter
• Three Separate Interrupts on TX Complete, TX Data Register Empty and RX Complete
• Multi-processor Communication Mode
• Double Speed Asynchronous Communication Mode
Overview
The Universal Synchronous and Asynchronous serial Receiver and Transmitter (USART) is a
highly flexible serial communication device.
The ATmega640/1280/2560 has four USART’s, USART0, USART1, USART2, and USART3.
The functionality for all four USART’s is described below. USART0, USART1, USART2, and
USART3 have different I/O registers as shown in “Register Summary” on page 414.
A simplified block diagram of the USART Transmitter is shown in Figure 22-1 on page 207. CPU
accessible I/O Registers and I/O pins are shown in bold.
The Power Reducion USART0 bit, PRUSART0, in “PRR0 – Power Reduction Register 0” on
page 56 must be disabled by writing a logical zero to it.
The Power Reducion USART1 bit, PRUSART1, in “PRR1 – Power Reduction Register 1” on
page 57 must be disabled by writing a logical zero to it.
The Power Reducion USART2 bit, PRUSART2, in “PRR1 – Power Reduction Register 1” on
page 57 must be disabled by writing a logical zero to it.
The Power Reducion USART3 bit, PRUSART3, in “PRR1 – Power Reduction Register 1” on
page 57 must be disabled by writing a logical zero to it.
206
ATmega640/1280/1281/2560/2561
2549L–AVR–08/07
ATMEL [ ATMEL ]
