VAX 4000-100 QBUS cables

Noel Chiappa jnc at
Tue Nov 29 19:56:53 CST 2016

    > From: Peter Coghlan

    > Interrupts would be great to have

If you decide you need interrupts, the DLV11 (MP-00055) has a simpile
interrupt circuit built out of flops and gates.

    > However, I am puzzled by the BPOK and BINIT signals being connected to
    > U7 even though they do not seem to get used ... I wonder is this just
    > because two tranceivers were left over and they might as well have
    > something connected to them that might come in handy later or is it
    > because I am failing to understand something properly?

Neither, but your first one is close! :-)

Actually, that design started as a CAD file (for KiCAD) that I got from Dave
B; I munged on it until it was what I wanted. Those two signals were
connected to that transceiver in Dave's original circuit; my design doesn't
(as you discovered) actually use BPOK or BINIT, so they just stayed connected
up, but unused.

    > there are rather more than 50 QBUS signals listed on the top right of
    > the circuit diagram.

As Glen indicated, it actually takes 2 50-pin connectors.

    > I suppose the power rails and those labeled "spare" are likely
    > candidates for omission.

I don't think they'd have carried power through that connector. The spare lines
might well be connected through.

I haven't checked the pinout of the 50-pin Berg headers (which were the
original, the 'D' connectors came later), but if they followed UNIBUS
precedent, every other wire in the flat cable will be a ground, to help
minimize cross-talk between lines with signals on them.

    > I was hoping that there would be lots of signal pairs like SCSI

Well, the QBUS wasn't designed to go through a cable, originally it was
backplane only; so it doesn't have differential pairs, or anything like that.


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