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

Johnny Billquist bqt at update.uu.se
Thu Feb 5 08:22:28 CST 2015

On 2015-02-05 15:00, Pete Turnbull wrote:
> On 05/02/2015 13:10, Noel Chiappa wrote:
>> 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.
>> 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....
> But you're supposed to plug in a Minimum Load card, aren't you?  I
> wonder if those slots would work for a non-DMA device.

Yes, and no.
You should plug in a MLM if you haven't fully populated the slots.
They are not wired up as Qbus slots.

>>      > I seem to remember that when two memory boards are used, they
>> should be
>>      > the same.
>> Really? That would surprise me.
> I don't believe that's true.  It's certainly not true in an 11/73 or
> 11/83, and I suspect the idea comes from one of the 11/84 manuals, which
> only mentions one type of card (half- or fully-populated).



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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