82511 - Serial Data Transfer Asynchronous v.s. Synchronous...

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Unformatted text preview: Serial Data Transfer Asynchronous v.s. Synchronous -- Asynchronous transfer does not require clock signal. However, it transfers extra bits (start bits and stop bits) during data communication -- Synchronous transfer does not transfer extra bits. However, it requires clock signal Frame Asynchronous Data transfer data Start bit B0 B1 B2 B3 B4 B5 B6 Stop bits Parity Synchronous Data transfer clk data B0 B1 B2 B3 B4 B5 11-1 8251 USART Interface 8251 D[7:0] RD WR A0 CLK RD WR C/D CLK TxD RxD TxC RxC RS232 A7 A6 A5 A4 A3 A2 A1 IO/M 11-2 Programming 8251 8251 mode register 7 6 5 4 3 2 1 0 Mode register Number of Stop bits 00: 01: 10: 11: invalid 1 bit 1.5 bits 2 bits Parity enable 0: disable 1: enable Character length 00: 01: 10: 11: 5 bits 6 bits 7 bits 8 bits Baud Rate 00: Syn. Mode 01: x1 clock 10: x16 clock 11: x64 clock Parity 0: odd 1: even 11-3 Programming 8251 8251 command register EH IR RTS ER SBRK RxE DTR TxE command register TxE: transmit enable DTR: data terminal ready RxE: receiver enable SBPRK: send break character ER: error reset RTS: request to send IR: internal reset EH: enter hunt mode 11-4 Programming 8251 8251 status register DSR SYNDET FE OE PE TxEMPTY RxRDY TxRDY status register TxRDY: RxRDY: TxEMPTY: PE: OE: FE: SYNDET: DSR: transmit ready receiver ready transmitter empty parity error overrun error framing error sync. character detected data set ready 11-5 Simple Serial I/O Procedures Read start Write start Check RxRDY No Check TxRDY No Is it logic 1? Yes Read data register* end Is it logic 1? Yes Write data register* end * This clears RxRDY * This clears TxRDY 11-6 ...
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82511 - Serial Data Transfer Asynchronous v.s. Synchronous...

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