On Thu, Jun 28, 2018 at 2:20 PM, Chuck Guzis via cctalk < cctalk@classiccmp.org> wrote:
> So, on a TIA/EIA/RS-232C DB-25 connector, what's the official position > on pin 1? The standards calls it PGND = Protective ground and most > reference seem to indicate that this is chassis/earth ground at both > ends of a cable. > Which is exactly why this kind of problem routinely happens with TIA/EIA-232 and RS-232. People try to run it hundreds of feet to somewhere with a significantly different ground potential, and if they're _lucky_, it only works badly, but often equipment gets damaged. Since -232 doesn't have any galvanic isolation, even if you don't ground pin 1 at one end, it will still have the same problem on signal lines, because ultimately they're referenced to ground at both ends. If you _must_ run a long -232 cable, you should use some kind of isolator at one end.
