The +/- 3 volts levels are requirements on the driver, not the receiver.
In practice, receivers have quite a small hysteresis, and the
threshold points are set to meet the requirements of a type 1 interface
as defined in section 7 of ITU-T V.28. Whilst the specified purpose of
this is that a powered down or open circuit condition should result in
defined states for, particularly control signals (off), in practice it
means that real world receivers will also handle high speed signals
which are strictly positive.
Consequently levels of +5 and 0 volts will, in most normal cases, work,
although they are out of specification.
ITU-T V.28 is generally aligned with the electrical characteristics of
EIA232, but has the advantage that the document is available for free
download.
--
David Woolley
Owner K2 06123
On 21/01/16 20:03, Cliff Frescura wrote:
RS-232 use +3 to +15VDC and -3 to -15VDC for signaling levels, thus -5 and +5
will work too, but *not* 0VDC and +5VDC
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