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

Pete Turnbull pete at dunnington.plus.com
Thu Feb 5 08:00:46 CST 2015

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.

>      > 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).

Pete						Peter Turnbull
						Network Manager
						University of York

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