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

Johnny Billquist bqt at update.uu.se
Wed Feb 4 13:38:57 CST 2015

Not a proper answer to Noel, but I've read that the FPA will not work in 
early CPU cards. Something wrong with the connections to the socket, I 
seem to recall (but it's just some impression from my reading).

Also, for some reason only a couple of variants are listed as usable in 
the 11/84. Might be some issues with detecting and handling the bus at 
the CPU in an 11/84 since the 11/84 usage of that bus differs from when 
it is used as an 11/83.

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.

And then of course, the J11 itself came in different variants with 
bugfixes. Not all J11 chips can even use the FPA.

ALl in all, that gives a lot of combinations. Some, I would suspect, 
would definitely be fixable by replacing some PAL.


On 2015-02-04 20:29, Henk Gooijen wrote:
> Oops,
> that was not the asked question!
> All I know about the /73 and /83 is the crystal, and the CPU "version"
> (-09).
> 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.
> Apologies for the previous post,
> - Henk
> -----Oorspronkelijk bericht----- From: Henk Gooijen
> Sent: Wednesday, February 04, 2015 8:22 PM
> To: General Discussion: On-Topic and Off-Topic Posts
> Subject: Re: Differences between PDP-11/83-84 M8190-AB/AC and AD/AE CPU
> cards
> Without any checking, just digging in my "grey cells", so I could be wrong
> ...
> The 11/84 has all of its memory "elsewhere", that is *not* on the CPU
> module.
> The 11/94 has *all* memory that can be addressed *on* the CPU module.
> So, the 11/94 has either 2MB or 4MB, what's installed on the module.
> The performance gain of the 11/94 over the 11/84 is in fact the local
> memory.
> If the 11/84 has 100% cache hits, it comes close to the 11/94. You could
> see
> the 11/94 as an 11/84 with all memory as cache memory.
> AFAIK, you cannot add memory to the 11/94 by adding a memory module
> on the bus. The memory must be on the CPU module.
> - Henk, PA8PDP
> -----Oorspronkelijk bericht----- From: Noel Chiappa
> Sent: Wednesday, February 04, 2015 6:40 PM
> To: cctalk at classiccmp.org
> Cc: jnc at mercury.lcs.mit.edu
> Subject: Differences between PDP-11/83-84 M8190-AB/AC and AD/AE CPU cards
> 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
> speed?
> 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!
> Noel

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