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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
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
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)
rs 232 cont
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
bandwidth
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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