11/45 hack?

tony duell ard at p850ug1.demon.co.uk
Sat Feb 7 12:53:25 CST 2015

>   The first 25 slots are for an initial "unibus a" terminator, cpu,
> floating point and memory, which, since I only have one bipolar matrix, is
> an enormous waste of like ten slots (they're wired for weird voltage and
> would presumably explode other boards installed there, right?).

Yes, AFAIK those memory slots are custom-wired so don't use them for
anything else.

>   So then there are three slots available at the end, 26, 27, 28 that are
> also marked "non-standard voltage."  I guess that means that putting normal
> boards in there is right out, too.  Anyway, the unibus out and bridge 9200
> jumper that connects unibus a and unibus b are supposed to go there.
> That's it for the main backplane.

You can put 3 quad-height SPC boards in there, if you don't then you have
to fit grant continuity cards. It's traditional to put the console DL11 there.

>   I'm going to duck after asking this, but would it be at all feasible to
> rewire the main 11/45 backplane to get rid of the weird voltages in those
> bipolar slots so they'd accommodate normal boards like these?

I am sure it's _possible_ but I wouldn't do it. The 11/45 is rare enough
as it is, I wouldn't make a permanent change to the CPU backplane. And
be warned it may not be an easy change, there's a PCB under all that wire-
wrap that carried power and ground at least. If you have to change any of 
that it is a _very_ big job.

>   Short of that, what can I do?  I definitely don't want another chassis.

Any reason not to have a 5.25" or 10.5" expansion box. From what I recall it is 
possible to drop the CPU and PSUs by 5.25" fairly easily so you should be able
to make room for the former.


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