KDJ11-B PDP 11/73 getting stuck in Exit standalone mode diag #56

Bill Gunshannon bill.gunshannon at hotmail.com
Wed Apr 5 10:02:55 CDT 2017

From: cctalk [cctalk-bounces at classiccmp.org] on behalf of Mark G Thomas via cctalk [cctalk at classiccmp.org]
Sent: Sunday, April 2, 2017 2:49 PM
To: cctech at classiccmp.org
Subject: KDJ11-B PDP 11/73 getting stuck in Exit standalone mode diag #56


I picked up an empty 4x8 Q-bus chassis at VCF-East this year. It's
labelled "USDC CSS-823 Processor System" on the outside. It's not a DEC
backplane, but the chassis is light aluminum, smaller and in some ways
nicer than my pile of BA23s. It includes a switching power supply,
LTC and q-bus termination, and I confirmed it's wired for Q22. I was
hoping to transplant an 11/83 into it, since it will fit more comfortably
in my work area. It has lit DCON/RUN/LTC/HALT buttons on the front pane.
The etching on the backplane says something like "MDB Systems, Inc.
East Orange, CA 92665"

Unfortunately, I discovered slots are all wired Q22/Q22, no top ABCD
(Q22/CD) PMI slots like a BA23. So, not good for an 11/83 CPU wired
for PMI on slots C-D.

So, I was hoping I could get my KDJ11-B (quad-wide 11/73) running in it.
Upon power up or reset I get "Testing in progress. Please wait" on
the serial console, and the LEDs get stuck on test 56. CTRL-C doesn't do
anything yet, and my only options seem to be to hit reset, or if I hit the
run/stop toggle, I can reset to the ODT prompt. This is with either just
the KDJ11-B in the top slot, or with the addition of a suitably configured
MSV11-QA in the next slot. If I turn off the LTC on the front panel,
I get the expected Error 61 M8190 clock error, PC and register values,
and options to re-run once or loop on test, so I know the LTC is working.

I confirmed the KDJ11-B works fine in a BA23, getting past test 56. I also
tried an 11/53 CPU here in the ABAB backplane and that gets past the self
tests into dialog mode, but I really would like to get the KDJ11-B working
in this chassis. I do see that a couple traces to the KDJ11-B C-D slots
besides the Grant Continuity connections. I assume since the KDJ11-B
has those Grant Continuity connections on slots C-D, it can run in a
qbus/qbus Q22/Q22 quad Q-bus slot.

I noticed the FP "RUN" lamp never comes on (and is not burned out), but maybe
that's normal -- monitoring something on the bus that doesn't happen during
power on self test.

Does anyone here have suggestions about next steps in diagnosing this?

4.10.18 Exit Standalone Mode (Test 56)

In the 22-bit mode, the exit standalone mode is checked by using the
guaranteed timeout address of 17 760 000 to verify that the timeout
logic works without hanging up the CPU.

Mark G. Thomas (Mark at Misty.com), KC3DRE

OK, I have the book on that.  You need to determine which backplane you have.
MLSI-BPA84-T    Serpentine A-B-A-B
MLSI-BPA84-A-T   Serpentine except for slots 6 and 7.

We'll ignore the MLSI-BPA82 as that's just a dual wide A-B.

I will see if I can scan the book and send it to you but no promises how
soon.  It's pretty good sized and my scanning capabilities are primitive.


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