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

Noel Chiappa jnc at mercury.lcs.mit.edu
Wed Feb 4 11:40:20 CST 2015

So I've seen some references which say that the M8190-AB and -AC (w-o/w FPJ11
FPP chip) are 15 MHz "11/73" CPUs for QBUS use, and the M8190-AD and -AE
(w-o/w FPJ11) are 18 MHz "11/83-84" CPUs for UNIBUS use (via the KTJ11-B
convertor, of course). (Of course, the /83 is nominally QBUS, but let's ignore
that for the moment... :-)

(And I'm not even going to try to give the KDJ11- suffixes that go with
these... :-)

However, I'm wondering if this is correct... I have a CPU board out of a 11/84
(one owned by DEC, no less!) which says M8190-AB on the handles, but the clock
crystal says "18.432", and it has a 57-19400-09 J11 chip, which seems to be
the 18MHz version (the 15Mhz seems to be -04).

Comparing it to a 'stock' -AB, this one seems to have the same 74S472 PROMs
(6 along the lower left-hand edge), PALs (top center and lower left), etc.
But they also match the ones on a 'stock' -AE, too!

So clearly an -AB/AC _can_ be _upgraded_ to an -AD/-AE... but are there
actually any differences between an -AB/AC and an -AD/-AE, other than the

I don't have my /84 up yet, so I can't plug a stock -AB in and see if it
works, but I'm starting to get the impression that except for the speed of the
J11 (and the crystal), and whether or not it came with the FPJ11, all four of
these boards are otherwise identical. Whether it's a 73, 83 or 84 depends
entirely on whether it has PMI memory and the KTJ11-B UNIBUS converter (and
the correct backplane, for the latter, of course).

Anyone have an confirmation one way or the other? Thanks!


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