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Chapter 5 Asynchronous Communication

Chapter 5 Asynchronous Communication. Sender and receiver do not synchronize before data transmission Receiver does not know when individual bits begin and end. RS-232 Standard. Used in async serial transmission Eg. Dumb terminals, terminal server, analog modems, console ports

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Chapter 5 Asynchronous Communication

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  1. Chapter 5 Asynchronous Communication • Sender and receiver do not synchronize before data transmission • Receiver does not know when individual bits begin and end

  2. RS-232 Standard • Used in async serial transmission • Eg. Dumb terminals, terminal server, analog modems, console ports • sender transmit character anytime • arbitrarily delay between characters • Binary 1 represented by –15 volts • Binary 0 represented by +15 volts • Idle voltage is –15 volts with minimum duration of one bit • Start bit (binary 0) sent before character • RS-232 voltage diagram (fig 5.2)

  3. RS-232 (cont.) • Baud rate • number of changes in the signal per second. • Bits per second may be equal to or greater than baud rate • Supports full duplex • DTE equipment (eg. computer) transmits on pin 2 and receives on pin 3 • DCE equipment (eg. modem) transmits on pin 3 and receive on pin 2 • Minimum 3 wires (fig 5.3) • DTR,DSR,DCD,RTS,CTS,TxD,RxD,GND • RTS/CTS used in hardware flow control

  4. Bandwidth • maximum rate (Hertz) that a transmission system can change a signal • Maximum theoretical data rate D (bits/s) for a transmission system with bandwidth B and uses K unique values of voltages: D = 2Blog 2 K (Nyquist’s theorem)

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