from
The Free On-line Dictionary of Computing (8 July 2008)
EIA-423
RS-423
<communications, standard> (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://rad.com/networks/1995/rs232/rs449.htm). Details
on RS-232, 422, 423 and 485
(http://rs485.com/rs485spec.html).
(2002-10-05)