11/73 into 11/03 chassis?

Jacob Ritorto jacob.ritorto at gmail.com
Mon Feb 8 17:55:44 CST 2016

This is extremely good info (thank you to Robert, Joseph and Noel!) and I
plan to do something like this someday when I get more q-bus stuff, but I
must apoligise for my inaccuracy because what I was originally trying to
ask was:

Can I tear apart my little BA23 (which currently has a power supply problem
and not enough space for my high capacity 8" SMD disks) and put the
Micro/PDP-11 backplane (with all its nice 11/73 cards and SMD disk
controllers, etc.) into the spot that my 11/03 backplane currently occupies
and run it via the (working) stock 11/03 power supply?  This "11/03
chassis" is bolted into what appears to be a common, official Digital 19"
rack surrounded by some RL02s, mid-height style (don't know the name of
this racking option).

  Specifically, would I have to butcher power and clock lines to do this,
or is it all plug compatible?  I'm considering tearing the systems down and
assessing the situation, but wanted to ask in advance in case somebody's
already gone there and can save me the heartache.  The recent mention of
the dual 11/73 in a 19" rack prompted me to reconsider my original intent
instead of rewiring old backplanes to be 22-bit compliant.


On Fri, Dec 11, 2015 at 8:19 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu>

>     > From: Jacob Ritorto
>     > Would you happen to have notes or references about how to do it?
> It's not too hard; basically, one has to wire pins BC1, BD1, BE1 and BF1
> (BDAL 18-BDAL21, respectively) on all _QBUS_ slots together into a bus. So
> wire BC1 on slot 1 to BC1 on slot 2, slot 3, etc, etc.
> A couple of notes: First, I said '_QBUS_' because if you have a Q/CD
> backplane, clearly one doesn't run the extra BDAL lines to the CD slots,
> only
> the QBUS slots (which run down the left-hand side, when facing the
> backplane).
> Second, for optimal analog behaviour, the 'out' slot on the backplane
> should
> be the last slot you wire to, so that there are no branches in the
> transmission line for BDAL18-BDAL21 (which can produce reflections - aka
> noise - on the transmission lines). How to do this efficiently (in terms of
> the wiring) can be a bit tricky, depending on the backplane configuration.
> E.g. if one has the standard 'serpentine' backplane, i.e. one with the
> slots
> in the following kind of order (facing the backplane from the board side):
> 1-2
> 4-3
> 5-6
> 8-7
> 9-10
> etc., one might naively think one has to run the extra bus lines back and
> forth to match. However, only the _grant_ lines have to follow this pattern
> (and they are already there); the added lines don't have to follow the same
> pattern, as long as there are no branches.
> So, for the example 5-slot backplane above, one could/would wire:
> 1-4-5-8-9--2-3-6-7-10
> i.e. a single vertical run on the left hand side, a single diagonal from 9
> back to 2 (shown with "--"), and then another vertical run on the right
> hand
> side. Much simpler than wiring back and forth in slot order; there are no
> branches; and the last slot is the 'out' slot.
> For backplane with an _even_ number of layers, e.g.:
> 1-2
> 4-3
> 5-6
> 8-7
> it's a little more complicated: a single vertical run on each side
> cannot be connected in such a way as to have the 'out' slot (8) be the
> last slot. One has to do something a little more complex:
> 1-4-5--2-3-6-7--8
> with a vertical run on the left side, stopping short of the last slot; then
> a vertical run on the right side, then a lateral back across on the last
> layer.
> Obviously one _could_ run the wires back and forth, in slot order, but that
> will take a lot more wire, which at the very least is more work (especially
> on backplanes which don't have full wire-wrap pins, just the little stubby
> pins that have to have the wires soldered to); whether it also increases
> the
> delay down those transmission lines enough to be noticeable is something I
> don't know the answer to.
> All the obvious caveats apply: make sure not to get confused by the mirror
> pin and slot numbers on the front and back sides (you'll be wiring on the
> back, whereas the diagrams above are on the front), etc.
>         Noel

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