Differences between PDP-11/83-84 M8190-AB/AC and AD/AE CPU cards

Noel Chiappa jnc at mercury.lcs.mit.edu
Sat Feb 7 17:17:55 CST 2015

    > From: Jerome H. Fine

    > With regard to the MSV11-JD in the PDP-11/84, was this board placed
    > after the KDJ11-AE board or before it?

After. The CPU _has_ to go in slot 1 on the 11/84 backplane. (I suspect, but
have yet to verify, that this is in part because bus grant lines are run
directly from that slot to the UNIBUS adapter slot.)

    > Also, has anyone ever used a KDJ11-AC board with the 15 MHz crystal in
    > the PDP-11/84 backplane? I can't see why it should not work, but just
    > maybe the PDP-11/84 backplane and a simple KDJ11-AC board are not
    > compatible.

Would a KDJ11-A board even work in an 11/84 backplane? It wouldn't (couldn't)
do the special PMI (actually, we ought to distinguish between 'QBUS PMI',
such as in the 11/83, and 'UNIBUS PMI', as in the 11/84; the second is a
superset of the first, I believe) protocol, so it wouldn't work with the
UNIBUS adapter.

See also Micronote #39, "Differences between KDJ11-A and KDJ11-B".


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