[Elecraft] Long RS232 Runs - RS422

[David Woolley]

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
>