UK PDP11 wanted

Johnny Billquist bqt at
Sat Apr 11 10:03:31 CDT 2015

On 2015-04-11 16:47, Noel Chiappa wrote:
>      > From: Johnny Billquist
>      >> a _system_ with an M8190, a KTJ11 (M8191), and no PMI memory, only
>      >> regular QBUS memory? (Not sure if this will work... but it should,
>      >> I'll try it soon and see.
>      > Should not work, as far as I know. The CPU bus on an 11/84 is always
>      > PMI.
> We had a prior discussion about this. Remember the jumpers I found on the
> 11/84 backplane? They can turn the PMI section (AFAICT) into a real QBUS. But
> that's if one wanted to use a QBUS _device_ in an 11/84 backplane (in the PMI
> part, of course).

I don't remember any jumpers. Maybe my memory is just short...

> For QBUS _memory_, it should 'just work', in the same way that you can plug
> an M8190 into a Q/CD backplane with some QBUS memory, and it will 'just
> work'. (I.e. the M8190 will automatically do QBUS memory cycles if that's the
> kind of memory that's out there.)

I'll believe that when you plug the Qbus memory *before* the CPU in a 
Q/CD backplane.

> Now, whether the _KTJ11_ will work properly with QBUS memory instead of PMI
> - no idea on that one! :-)

That is also, obviously an important part here.


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

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