PDP-11/84 Qbus slots for memory

Paul Anderson useddec at gmail.com
Mon Jul 23 09:18:15 CDT 2018

Hi Mark,

If you want to borrow one to try it, let me know.


On Mon, Jul 23, 2018 at 8:59 AM, Noel Chiappa via cctalk <
cctalk at classiccmp.org> wrote:

>     > From: Charles Dickman
>     > an 11/84 with the UNIBUS adapter and PMI memory does not have a Qbus.
>     > ... the KDJ11-B (M8190) bus protocols change when a KTJ11 (UNIBUS
>     > adapter) is present and so what would be expected to be Qbus isn't.
> Ah, excellent point.
> Looking at the description of the CPU/UBA adapter in the KDJ11-B User
> Manual
> (EK-KDJ1B-UG-001, pp. 7-6 to 7-9), the answer is not certain; it all
> depends
> on implementation details on the CPU card which aren't described.
> E.g. the DMA cycle _might_ work, it all depends on what happens at step 8
> when, instead of PBSY being asserted, BSYNC is asserted. The _memory_ will
> be
> fine (since in an -11/83, this kind of thing is expected)... but the _CPU_,
> who knows.
> Interrupt cycles are more problematic; the assertion of the interrupt level
> on the BDAL lines (step 1a) will probably pass, but step 6 (assertion of
> BSACK) may be an issue, since the device will want to assert BRPLY instead
> (BSACK is not used in a QBUS interrupt), and the CPU may not do the right
> thing.
>     > I think there was a DEC Micronote that explained the protocol
>     > modifications involved.
> I don't think so; #30 "PMI on KDJ11-B and MSV11-J" describes the _basic_
> PMI, but the interaction with the UBA isn't described there. But the
> KDJ11-B User Manual has it in some detail.
>         Noel

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