[Elecraft] Long RS232 Runs - RS422

[Cliff Frescura]

"Consequently levels of +5 and 0 volts will, in most normal cases, work,
although they are out of specification"

Yes, they work by accident.  Until they don't.

73,

Cliff K3LL

-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of David
Woolley
Sent: Friday, January 22, 2016 6:45 AM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] Long RS232 Runs - RS422

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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