Question about UNIBUS terminators, M9300

Noel Chiappa jnc at
Thu May 26 08:38:43 CDT 2016

    > From: William Degnan

    > Here is the layout starting from slot 9/11 of the expansion cabinet

Just slot numbers by themselves aren't much use, because if there are any
non-UNIBUS backplanes (e.g. custom backplanes for core memory, for an RH11 -
which has its own custom backplane, you can't use a regular SPC/MUD 'UNIBUS'
backplane to hold it), we need to know what those are, and where.

Note that many boards can only go in a specific slot in a custom backplane,
and vice verse - some slots in such backplanes will only hold a specific kind
of card.

Taking the RH11-AB as an example: it comes with a 9-slot custom backplane. Hex
RH11 boards M7294 and M7295 go in slots 3 and 2, respectively (and nowhere
else, and nothing else can go in those slots). UNIBUS A in is in slot 1,
connectors A/B; UNIBUS A out is in slot 9, connectors A/B. UNIBUS B in is in
slot 8, connectors A/B; UNIBUS A out is in slot 7, connectors A/B.

The RH11 backplane has some slots which are not needed/used by the RH11; those
are wired as SPC slots; slots 7, 8 and 9, connectors C-F (the A-B connectors
in these slots are UNIBUS, per above), are SPC slots. That means that they
need _at least_ a G727 single-width card (the little square grant continuity
cards which jumper BG4-7) in them if there is no other device plugged in. If
the NPG wire-wrap jumper on the backplane for that slot has been removed,
you'd have to use a G7273 dual-width jumper card, to jumper NPG also.

So, looking at your list; first, a comment about naming:

  9/11: M9202 (1-2)
  11: M7297 (3-4)
  11: 7296 (5-6)

This looks like slot 1 of an RH11 backplane. Standard practise it to use
letters for the vertical, and numbers for the horizontal, for positive
identification. So standard nomenclature would be to say that the M9202 is in
connectors A/B, the M7297 in C/D, and the M7296 in E/F.

(Individual pins are named xYZn, where 'x' is the slot, 1-N [where N is
typically 4 or 9]; 'Y' is the connector, A-F; 'Y' is the pin, A-V using the
'DEC alphabet'; and 'n' is the side, 1-2. The NPG jumper is CA1-CB1 in all
SPC/MUD slots, i.e. 1CA1-1CB1 in slot 1.)

The stuff starting in slot '21' looks like a DB11 UNIBUS repeater, but I have
no idea how large a backplane that is, and what the various slots/connectors
in it are used for. It's almost certainly custom wired.

It looks like slot 31 starts another backplane. Given the cards that are
plugged in (LP11, DL11, etc), it's probably a 'UNIBUS' backplane (i.e. SPC or
MUD slots).


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