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Asynchronous transmission over RS232

Discussion in 'Hardware' started by Dom, Oct 21, 2003.

  1. Dom

    Dom Guest

    Hi,

    I understand how asynchronous transmission works but I don't quite
    understand how the receiver synchronises with the transmitter. At 1bps
    (just to make the figures easy) the transmitter is changing the
    voltage on the serial line to indicate a 1 or a 0 (-3 to -12 for a 1
    and +3 to +12 for a 0) every second if there is a change from 1 to 0
    or 0 to 1. The receiver synchronises on a change from the idle state
    i.e. logical 1 to logical 0 (the start bit). The receiver then
    re-sets its clock to sample in the centre of each transmitted bit.
    How does the receiver spot the change from idle state to start bit
    unless it is sampling the line more frequently than once / second?


    TIA

    Dom
     
    Dom, Oct 21, 2003
    #1
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