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42073A-MCU Wireless-02/13
ATmega2564/1284/644RFR2
23 USART
23.1 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
3 separate interrupts on TX complete, TX data register empty and RX complete
Multi-processor communication mode
Double speed, asynchronous communication mode
23.2 Overview
The Universal Synchronous and Asynchronous Serial Receiver and Transmitter
(USART) is a highly flexible serial communication device.
The ATmega2564/1284/644RFR2 has two USART’s, USART0 and USART1. The
functionality for all two USART’s is described below. USART0 and USART1 have
371 on page 371. CPU accessible I/O registers and I/O pins are shown in bold.
196 must be disabled by writing a logical zero to it.
main parts of the USART (listed from the top): clock generator, transmitter and receiver.
Control registers are shared by all units. The clock generation logic consists of
synchronization logic for external clock input used by synchronous slave operation, and
the baud rate generator. The XCKn (transfer clock) pin is only used by synchronous
transfer mode. The transmitter consists of a single write buffer, a serial shift register,
Parity generator and control logic for handling different serial frame formats. The write
buffer allows a continuous transfer of data without any delay between frames. The
receiver is the most complex part of the USART module due to its clock and data
recovery units. The recovery units are used for asynchronous data reception. In
addition to the recovery units, the receiver includes a parity checker, control logic, a
shift register and a two level receive buffer (UDRn). The receiver supports the same
frame formats as the transmitter, and can detect frame, data overrun and parity errors.