Datasheet

130
ATmega8(L)
2486M–AVR–12/03
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 acces-
sible I/O Registers and I/O pins are shown in bold.
Figure 61. USART Block Diagram
(1)
Note: 1. Refer to “Pin Configurations” on page 2, Table 30 on page 62, and Table 29 on page
62 for USART pin placement.
PARITY
GENERATOR
UBRR[H:L]
UDR (Transmit)
UCSRA UCSRB UCSRC
BAUD RATE GENERATOR
TRANSMIT SHIFT REGISTER
RECEIVE SHIFT REGISTER RxD
TxD
PIN
CONTROL
UDR (Receive)
PIN
CONTROL
XCK
DATA
RECOVERY
CLOCK
RECOVERY
PIN
CONTROL
TX
CONTROL
RX
CONTROL
PARITY
CHECKER
DATABUS
OSC
SYNC LOGIC
Clock Generator
Transmitter
Receiver