28 Jun
2018
28 Jun
'18
1:42 p.m.
On Thu, Jun 28, 2018 at 2:20 PM, Chuck Guzis via cctalk <
cctalk at 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.