AT90S8515_01 Datasheet, PDF (52/112 Pages) ATMEL Corporation – 8-bit Microcontroller with 8K Bytes In-System Programmable Flash

UART
Data Transmission
The AT90S8515 features a full duplex (separate receive and transmit registers) Univer-
sal Asynchronous Receiver and Transmitter (UART). The main features are:
• Baud Rate Generator that can Generate a large Number of Baud Rates (bps)
• 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
A block schematic of the UART transmitter is shown in Figure 38.
Figure 38. 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.
52 AT90S8515
0841G–09/01