[TUHS] PDP 11/34a Serial Communications Problem

Noel Chiappa jnc at mercury.lcs.mit.edu
Mon Feb 6 06:38:28 AEST 2017


    > From: Mark Hare

    > For a more permanent solution, I designed a simple adapter board that
    > connects to the BERG 40 connector on the DL11-W and converts it to a DB9
    > serial port ...  I also ordered a 40-pin (non-IDE) ribbon cable to
    > connect the DL11-W to my adapter.

    > When I connected everything, the 11/34 would start but no lights would
    > appear on the front panel. I tried disconnecting the adapter but leaving
    > the ribbon cable plugged into the BERG connector, but the problem
    > persisted. When I removed the ribbon cable entirely, the unit powered on
    > with no problems.

That's extremely odd. There isn't a pin on the DL11-W Berg connector which
should be able to cause anything like that kind of behaviour. The only
_possible_ thing I can think of, looking at the list of signals on the Berg,
is that you are grounding +5 (TT). Either that, or your DL11-W has some
serious issue?

    > Since this is a straight-through ribbon cable, I don't see what could be
    > causing this problem.

Me either. But clearly it's not just a straight-through ribbon cable....

I myself wouldn't have gone that route; one can obtain 40-pin IDE/DuPont (they
are all .1" spacing pins, and basically interchangeable, module keying)
connector shells, and female pins for same; I would have made a custom cable
to plug into the Berg with that, to a DE-9S or DB-9P connector (depending on
whether one wanted one wired as a DCE or DTE). (I myself make such cables, but
to a DB-25S connector, and then use a commercial DB-25P to DE-9S adapter when
needed.) Oh well...

Does the DL11-W still work, using the jumper cables kludge? 

    Noel


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