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UART Overview

UART Overview. Transmitting and Receiving Serial Data. The ABC’s of Serial Ports. UART = Universal Asynchronous Receiver/Transmitter TX = Transmitter RX = Receiver TD = Transmit Data (Data output) RD = Receive Data (Data input) RTS = Request to Send (Flow control output)

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UART Overview

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  1. UART Overview Transmitting and Receiving Serial Data BYU ECEn 320

  2. The ABC’s of Serial Ports • UART = Universal Asynchronous Receiver/Transmitter • TX = Transmitter • RX = Receiver • TD = Transmit Data (Data output) • RD = Receive Data (Data input) • RTS = Request to Send (Flow control output) • CTS = Clear to Send (Flow control input) • Half Duplex – transmits one direction at a time (mostly obsolete now) • Full Duplex – transmits both directions at the same time • RTS/CTS Flow control for full duplex serial ports : • RX assert RTS when it is ready to receive • TX waits for CTS before transmitting BYU ECEn 320

  3. Serial Port Devices The following is a list of various hardware components that use Serial Ports : • Mouse - One of the most commonly used devices for serial ports. • Modem - Used commonly with older computers. • Network - One of the original uses of the serial port, which allowed two computers to connect together and transfer large files between the two. • Printer - Mostly used with older printers only. • ASCII Terminal (TTY) - Like the Hyperterm interface. BYU ECEn 320

  4. Hooking Up Two Serial Ports Full Duplex TD RD RTS CTS GND TD RD RTS CTS GND BYU ECEn 320

  5. Hooking Up Two Serial Ports Full Duplex TD RD RTS CTS GND Cable TD RD RTS CTS GND BYU ECEn 320

  6. Serial PortonSpartan 3 Board DCD DSR RXD RTS TXD CTS DTR RI BYU ECEn 320

  7. Connectionto PC BYU ECEn 320

  8. Serial Communication Format • Data is transmitted sequentially, one bit at a time. • To inform the receiver that a new byte is arriving, a “start bit” (a zero) is sent first. A start bit can start at any time. • Then the data is transmitted, LSB (least significant bit) first, and MSB (most significant bit) last. • At the end, zero, one or two “stop bits” (ones) are transmitted. • A frame consist of : • 1 start bit (a zero) • 7 or 8 data bits LSB (least significant bit) first • 1 optional parity bit • 0, 1 or 2 stop bits (ones) • Between transmissions, the transmitter transmits a high. • The bit time is determined by the baud rate which is given in units of BPS (bits per second). • Transmitter and receiver do not share a clock (hence the asynchronous nature). BYU ECEn 320

  9. Serial Frame http://www.atmel.com/dyn/resources/prod_documents/DOC0941.PDF http://www.wcscnet.com/Tutorials/SerialComm/Page1.htm BYU ECEn 320

  10. Transmitting BYU ECEn 320

  11. Receiving 1.5 bit time 1.5 bit time BYU ECEn 320

  12. Receiver Sample Timing Slightly Faster Baud Rate Exact Baud Rate Slightly Slower Baud Rate 1BitTime 1.5Bit Time BYU ECEn 320

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