[rescue] Trying to get Cadmus 9200 running (serial console trouble)

Mouse mouse at Rodents-Montreal.ORG
Wed Feb 6 06:36:38 CST 2019

>> Hmmm.  Is it possible that it's a differential serial line, like
>> RS423 or similar?  If that's the case, if the other line of the
>> differential pair isn't grounded, I've seen exactly this sort of
>> behavior.
> Docs say it's standard RS-232.

> Perhaps I just got some not connected pin to PC side Rx and the cable
> picked up some noise?

Could be, but, I would say, unlikely.  My experience, while limited, is
that such a thing is unlikely to produce mostly-working echo.

There is a first time for everything, though....

> But that seems unlikely as RS-232 should not pick up anything below
> +-3V and "antenna" should not induce volatages over 3V here, I think.

If the receiver impedance is high enough it certainly can.  Serial-line
drivers have to be relatively low impedance, but I don't think the spec
puts any cap on receiver impedance (and even if it did I've seen enough
manufacturers playing fast and loose with RS-232 that it would not
surprise me to see such a spec, if there is one, ignored).

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