pete at dunnington.plus.com
Mon Dec 12 16:01:12 CST 2005
On Dec 12 2005, 16:20, Allison wrote:
> > From: Pete Turnbull <pete at dunnington.plus.com>
> >All the ones I've ever seen in the field are the same regardless of
> >whther for microPDP-11 or microVAX. I can't see why the microVAX
> >would be different; the microPDP has the CD slots for PMI but the
> >microVAX doesn't care -- it uses over-the-top connections for the
> >The BA23 backplane for a microPDP-11 is an H9278-A and does indeed
> >three slots Q22-CD followed by five serpentine Q22-Q22. That's the
> >same as my microVAX. And that agrees with the Tech Manuals I have.
> Ah, but it doesnt agree with mine. You can use the H9278 for Qbus -11
> but if you want to maximize the slots there was a differnt early
> BA23 that had no CD slots(all were AB serpentine) as none of the
> processors before the PMI equipped 11/73 used PMI. Early
> wer really 11/23Bs. As a result there really were two similar but
> not exactly the same flavors.
OK, but that would be unusual, and not exactly standard :-) Was that
a protoype? You could certainly use Q22-CD slots for 11/23-compatible
memory -- yes, I know the microPDP11/23 is just a KDF11-B with
different ROMs -- and I've never seen a BA23 that wasn't 3 x Q22-CD
plus 5 x Q22-Q22, which is what the tech manuals and maintenance
manuals I have describe. I don't even know of any other 4 x 8
backplane that could fit.
> I know the gory details as my BA23 uVAX
> was hacked from the uPDP-11 and I needed a differnt backplane
> (memory compatability) and the front pannel insert for the drive
> control was different.
Well if you started with a fully-serpentine Q22-Q22 backplane, the
microVAX memory would need it changed, because the cards talk to each
other using the CD-interconnect, which I'd forgotten (but not AFAIK for
CPU/memory transfers, which are over the top). The front panel,
though, is the same except for the badge, everywhere I've seen. The
console/SLU panel, the *back* panel, is different, of course.
Pete Peter Turnbull
University of York
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