ATmega8(L)
USART
The Universal Synchronous and Asynchronous serial Receiver and Transmitter (USART) is a
highly-flexible serial communication device. The main features are:
• 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 Databits 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
A simplified block diagram of the USART Transmitter is shown in Figure 61. CPU accessible I/O
Registers and I/O pins are shown in bold.
Figure 61. USART Block Diagram(1)
Clock Generator
UBRR[H:L]
OSC
BAUD RATE GENERATOR
SYNC LOGIC
PIN
XCK
CONTROL
Transmitter
TX
CONTROL
UDR (Transmit)
PARITY
GENERATOR
PIN
CONTROL
TRANSMIT SHIFT REGISTER
TxD
Receiver
CLOCK
RX
RECOVERY
CONTROL
DATA
RECOVERY
PIN
CONTROL
RECEIVE SHIFT REGISTER
RxD
PARITY
CHECKER
UDR (Receive)
UCSRA
UCSRB
UCSRC
Note:
1. Refer to “Pin Configurations” on page 2, Table 30 on page 64, and Table 29 on page 64 for
USART pin placement.
133
2486T–AVR–05/08
ATMEL [ ATMEL ]
