Datasheet

171
2490R–AVR–02/2013
ATmega64(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 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
Dual USART The ATmega64 has two USART’s, USART0 and USART1. The functionality for both USART’s is
described below. USART0 and USART1 have different I/O Registers as shown in “Register
Summary” on page 392. Note that in ATmega103 compatibility mode, USART1 is not available,
neither is the UBRR0H or UCRS0C registers. This means that in ATmega103 compatibility
mode, the ATmega64 supports asynchronous operation of USART0 only.
Overview A simplified block diagram of the USART Transmitter is shown in Figure 79. CPU accessible I/O
Registers and I/O pins are shown in bold.
Figure 79. USART Block Diagram
(1)
Note: 1. Refer to Figure 1 on page 2, Table 36 on page 78, and Table 39 on page 81 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
DATA BUS
OSC
SYNC LOGIC
Clock Generator
Transmitter
Receiver