Henk Gooijen henk.gooijen at hotmail.com
Wed Jun 1 12:50:20 CDT 2016

-----Oorspronkelijk bericht----- 
From: Noel Chiappa 
Sent: Wednesday, June 01, 2016 7:24 PM 
To: cctalk at classiccmp.org 
Cc: jnc at mercury.lcs.mit.edu 
Subject: Re: PDP-11/94-E 

    > From: Henk Gooijen

    > The first 4 (5?) slots are QBUS

Technically, PMI, which is more-or-less QBUS on the left (A/B) side (modulo
not having grants, unless the appropriate backplane jumpers are set to send
grants to those slots), and it uses the standard CD interconnect (as in Q/CD
backplanes) on the right (C/D) side to carry PMI.

    > The RX211 must have the NPR/NPG open. Check the documention which DIP
    > switch must be set in the correct position. However, not sure if that
    > would cause the RX211 to be "invisible".

Right; DMA would not work, but normal master/slave UNIBUS read/write cycles
to the device registers should still work.


You can of course read and write the CSR and all other registers of the RX211,
*if* it is in the memory space where you expect it. Making sure is easy: check
the jumpers / DIP switches on the RX211.
Note that the RX11 (for RX01 drives) does *not* use DMA, and what's worse
(IIRC) that module does NOT jumper CA1-CB1 on the module itself!
The RX211 does use DMA, so the NPG should be open. As said, there is no
need to cut the NPR/NPG wire, because those two pins  go to that first module
at the right side, and has a DIP switch to open / close the NPR/NPG for *all*
UNIBUS slots).
But this is all from memory ... you can read the manual from bitsavers too ;-)
BTW, yes I have an 84 and an 94 in that box (power supply at the right side
of the box). Very similar in all aspects.  In fact, DEC did "rebrand" an 84 to
an 94 by swapping the CPU module (and removing the memory modules),
and glueing a label saying PDP-11/94 over the original panel's PDP-11/84.
I have such a box too. Hmmm, should take a picture of that ...

- Henk

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