Rainbow Electronics AT90LS4433 - Manual (Page 53)

53
AT90S/LS4433
1042G–AVR–09/02
UART
The AT90S4433 features a full duplex (separate Receive and Transmit Registers) Uni-
versal Asynchronous Receiver and Transmitter (UART). The main features are:
•
Baud Rate Generator Generates any Baud Rate
• High Baud Rates at Low XTAL Frequencies
• 8 or 9 Bits Data
• Noise Filtering
• Overrun Detection
• Framing Error Detection
• False Start Bit Detection
• Three Separate Interrupts on TX Complete, TX Data Register Empty, and RX Complete
• Multi-processor Communication Mode
Data Transmission A block schematic of the UART Transmitter is shown in Figure 40.
Figure 40. UART Transmitter
Data transmission is initiated by writing the data to be transmitted to the UART I/O Data
Register (UDR). Data is transferred from UDR to the Transmit Shift Register when:
• A new character has been written to UDR after the stop bit from the previous
character has been shifted out. The Shift Register is loaded immediately.
• A new character has been written to UDR before the stop bit from the previous
character has been shifted out. The Shift Register is loaded when the stop bit of the
character currently being transmitted has been shifted out.
When data is transferred from UDR to the Shift Register, the UDRE (UART Data Regis-
ter Empty) bit in the UART Control and Status Register A, UCSRA, is set. When this bit
is set (one), the UART is ready to receive the next character. At the same time as the
UART CONTROL
AND STAUS
REGISTER B (UCSRB)
UART CONTROL
AND STAUS
REGISTER A (UCSRA)