pdp11/84 PMI memory: What is the problem with Q bus?

Noel Chiappa jnc at mercury.lcs.mit.edu
Fri Apr 24 14:01:23 CDT 2020

    > From: Jerry Weiss

    > Sorry about the uNOTE confusion..

No problem, it only took me about a minute to find the right one; my note was
to warn other people who didn't know about the number duplication.

    > If you look at the Memory Comparison table in this OEM uNOTE, it only
    > lists Block Mode for "JD/JE ONLY".

Oh, right. Still, it sounds from reports here like regular DMA doesn't work
in QBUS mode either - and technically that table entry might mean than since
it doesn't work for the QBUS _at all_, that includes no block mode.

I actually have -B/-C boards, I should plug one in in QBUS mode, and get my
QSIC prototype working again (it somehow random failed during the last year,
and I've been too lazy to debug it), and write a little program to DMA blocks
in and out, and see what happens to the data. If I get really energetic I
could throw a 'scope on the bus and look at bus cycles and see if they look

It would be interesting to have some more detail on the failure.


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