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

Noel Chiappa jnc at mercury.lcs.mit.edu
Thu Feb 5 07:10:24 CST 2015

    > From: Henk Gooijen

    > Maybe a few PALs have to be a faster version, but I do not expect that.
    > The 15 MHz to 18 MHz is not that big of a difference.

I did wonder about that, but they boards use parts from a number of different
chip companies (both the PALs, and the PROMs), so since I don't know how to
read those parts for speed variants, I couldn't say.

    > From: Johnny Billquist

    > The 11/84 variant is pretty much a PMI bus all the way, but I seem to
    > remember a couple of signals defined differently even in the 11/84
    > compared to the 11/83.

If you run across where you saw that, I'd be curious. The 84's use is, as you
point out, different, since it includes the CPU<->UNIBUS adapter protocol for
UNIBUS cycles. But I would have assumed that it was a plain superset of the
83's (not that I have read much about 11/83's... :-).

    > From: Jerome H. Fine

    > The MSV11-JB (1 MB) and MSV11-JC (2 MB) are used in the PDP-11/84. The
    > MSV11-JD (1 MB) and the MSV11-JE (2 MB) are used in the PDP-11/83.

Err, not sure this is correct: I got an 11/84 with an MSV11-JD in it. As
someone pointed out in a later message, the difference between the B/C and
D/E is that the B/C only work as PMI memories, their QBUS functionality has
some issues (IIRC, something to do with QBUS block transfers not working

    > In addition, for at least the PDP-11/83, the PMI memory must be placed
    > into the backplane ahead of the CPU for the memory to function as PMI
    > memory. That may be the only position allowed for the memory for the
    > PDP-11/84.

The 11/84 backplane has two special Q22/CD slots after the processor slot
which the memory goes in, with the CD sections wired to through-connect the
PMI pins.

I have this sneaking suspicion that the Q22 portions of those two slots aren't
_real_ QBUS slots (so you can't plug a QBUS device into them if you aren't
using them for memory :-), because I suspect they didn't run BIAK and BDMG to
those slots, but rather piped them directly to the UNIBUS adapter slot. My
reasoning for that is that if you don't plug in a memory card in one of those
slots, you don't have to plug in a grant continuity card, so.... Anyway, I
have a spare 11/84 backplane, and one day I'll get around to poking at it with
an ohmmeter to verify that suspicion.

    > I seem to remember that when two memory boards are used, they should be
    > the same.

Really? That would surprise me.


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