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

Johnny Billquist bqt at update.uu.se
Thu Feb 5 07:59:18 CST 2015

On 2015-02-05 14:10, Noel Chiappa wrote:
>      > 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.

I also would not expect the frequency to be a problem. However, as the 
Qbus/PMI differs from the 11/84 CPU bus, there can be chips that don't 
work correctly in one or the other.

>      > 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... :-).

I actually know where I read up on that. The 11/84 system manual 
documents the CPU bus, including differences.

chapter 2.2, which both documents the PMI bus, and in which way it 
changes when it sits in an 11/84.

I might have also read some other manuals that give me information, but 
this was the quickest I could find right now.

One obvious difference, by the way, is the fact that when you have a 
Qbus system, memory must sit to the right (top of) the CPU in order to 
use the PMI bus, while in an 11/84, the memory sits to the left (below) 
the CPU, while still using a modified PMI protocol.

>      > 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
> correctly).

As other have pointed out, Jerome is not correct.

>      > 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.

Right. The 11/84 backplane is wired differently. The CPU goes in the 
first slot in an 11/84 system.
And slots 2 and 3 are not Q-CD slots.

> 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.

Correct. They are *not* qbus. Don't even try plugging any Qbus cards in 

>      > I seem to remember that when two memory boards are used, they should be
>      > the same.
> Really? That would surprise me.

Not true. You can put a two meg and a one meg card into the system 
together. Done that in the past. Works just fine.


Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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