Thicknet/10base5 Test Segment: The Cable is In!

[Eric Smith]

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.