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

Brent Hilpert hilpert at cs.ubc.ca
Wed Feb 4 20:53:45 CST 2015

On 2015-Feb-04, at 6:10 PM, Pete Turnbull wrote:
> On 04/02/2015 17:40, Noel Chiappa wrote:
>> 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... :-)
>> 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).
> There were various revisions of the J11 chip, which was originally
> designed to run rather faster (more than 20MHz) than early ones were
> found to be capable of reliably.  So "slow" ones were clocked at 15MHz and sold as 11/73 boards, faster ones clocked at 18MHz and sold as 11/83 (or later as /84 - there's no difference at all in the boards).  To further differentiate the two, DEC arranged 11/83s with PMI memory, and 11/73s with normal QBus memory, but both boards are capable of running in either memory configuration.  Additionally, 11/83s normally had the FPA as standard.

This is all interesting, does anyone have a reference/source for the J11 part # suffix vs. clock speed?

I was wondering about J11 clock speeds a few months ago, mostly out of curiousity, while working on a little project,
(leaving aside clock speed, PDP11 geeks might find it mildly amusing):


Notice the link in there to an article by Bob Supnik that refers to clock speeds down in the 3-5 MHz range. I wonder what's going on there - if what Bob is saying is accurate how did this chip design ever reach 15/18/20MHz?

The J11 I have has a suffix of -08, and 1987 date code.

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