[TUHS] PDP 11/34a Serial Communications Problem

Michael Kjörling michael at kjorling.se
Mon Feb 6 06:36:38 AEST 2017

On 5 Feb 2017 15:03 -0500, from markhare at buffalo.edu (Mark Hare):
> Since this is a straight-through ribbon cable, I don't see what could be
> causing this problem. I have checked the continuity of each wire in the
> cable, and there doesn't appear to be a problem. I'd appreciate any advice
> that anyone has to offer.

Have you checked to make sure that there aren't any connections
between the individual wires? I'm not particularly familiar with the
hardware of the PDP-11, but a signal going out on one wire and showing
up also on some should-be unrelated wire could conceivably cause all
kinds of weird behavior depending on exactly which wires are involved
and what they are used for.

The fact that merely leaving the ribbon cable connected causes the
problem to appear definitely points to the PDP-11 not agreeing with
the cable (or connections) for some reason. My first suspect in that
case would be an electrical problem with the cable itself _versus what
the PDP-11 wants it like_. Maybe the cable is operating to
specifications, but the '11 wants something different.

Michael Kjörling • https://michael.kjorling.semichael at kjorling.se
                 “People who think they know everything really annoy
                 those of us who know we don’t.” (Bjarne Stroustrup)

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