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

Pete Turnbull pete at dunnington.plus.com
Wed Feb 4 20:10:59 CST 2015

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.

Another variation comes about because bugs in early revisions of the J11
CPU and the corresponding gate arrays meant they didn't work properly
with the FPA.  But most 11/73 (15MHz) boards are OK.

> 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).

Correct.  And in fact if you run XXDP or any other DEC software that
tests for 73/83ness, you'll find the result depends entirely on where
the memory is, and not on anything else.  Also if you're lucky, and keep 
the system well inside the designed temperature range and loading, you 
can even upgrade the crystal oscillator on an 11/73.

As to the difference between the M8190 in an 11/83 and that in an 11/84, 
there is none.  But IIRC there's a difference in the way one signal is 
used on the backplane, and IIRC (again) the earliest 11/83 ROMs may not 
work properly in an 11/84.


Pete Turnbull

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