Allison wrote:
Jerome Fine
replies:
As far as I understand, a 22 bit PDP-11/23 and all
PDP-11/73 systems use the same memory as the uVAX-I.
That would seem to indicate that the same backplane
can be used for either CPU in a BA23 box. As for a
uVAX-II, I can remember using the SAME box for BOTH
a PDP-11/73 and a uVAX-II system at least 5 years ago.
There were Q22 and Q18.
The CD side of the indicated backplanes were notably different.
It's my uderstanding the uVAX-1 had a special backplane to
accomodate non-PMI memory and there were some power wiring
differences that were dangerous to AB wired cards.
One BA23 I got has a Q22 with all slot pairs AB/CB wired Q22
in a serpentine pattern.
All three BA23s came from internal to DEC.
Jerome Fine replies:
That would explain the situation since no one else seems
to have ever seen a pure Q22 backplane for a BA23.
Since I can use a BA23 box with a PDP-11/73 with BOTH
normal memory below the CPU and PMI memory above the
CPU (actually, it can even be the same memory), the
uVAX-I should also be able to do so as well. However,
for a pure Q22 backplane will all slots wired AB /AB
(I presume that is what you really meant to write),
PMI memory would not be possible for the PDP-11/83.
I presume that would also preclude a uVAX-II which I
assume also needs AB / CD slots as well.
On the other hand, if all the slots were wired as
AB / CD as in an BA213 box (is BA213 correct - that
would be for a uVAX-III) which has only AB / CD, the
PDP-11/73 should also work along with the PDP-11/83
although I have never hear of anyone using these
boxes for PDP-11 CPUs since they require different
boards which likely are not available to be used with
the PDP-11 in most cases. Tony, do you have a UVAX-III
box or can anyone else comment?
Note that a BA11-S box is a 22 bit 4 * 9 backplane and
wired AB / CD for all 9 Qbus slots. One of these years
I will try using a PDP-11/83 and PMI memory to test
the situation.
Sincerely yours,
Jerome Fine
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