资料来源 : Free On-Line Dictionary of Computing

EIA-423
     
         (Formerly "RS-423") An {EIA}
        {serial line} {standard} which specifies {single ended}
        communication.  The mechanical connections for this interface
        are specified by {EIA-449}.  Although it was originally
        intented as a successor of {EIA-232} it is not widely used.
        The {EIA-232} standard has its limits at 20kbps and 1.5m.
        EIA-423 can have a cable lenght of 1200m, and achieve a data
        rate of 100Kbps.  When no data is being transmitted, the
        serial line is at a logical zero (+3 to +15 Volts).  A logical
        one is represented as a signal level of -15 to -3 Volts.  In
        practise, one often finds signals which switch between
        nominally +4.5 and +0.5 Volts.  Such signals are large by
        modern standards, and because the impedance of the circuits is
        relatively high, the allowable bit rate is modest.  The data
        is preceded by a start bit which is always a logical
        one.  There may be seven or eight bits of data, possibly
        followed by an even or odd parity bit and one or two stop
        bits.  A "break" condition is a continuous logical one on the
        line which is what would be observed if nothing was connected.
     
        {Comparing EIA-422, 423, 449 to RS-232-C
        (http://www.rad.com/networks/1995/rs232/rs449.htm)}.  {Details
        on RS-232, 422, 423 and 485
        (http://www.rs485.com/rs485spec.html)}.
     
        (2002-10-05)