DEC M9312 Configs for a 11/40

Josh Dersch derschjo at
Mon Nov 28 21:51:15 CST 2016

On 11/28/16 6:46 PM, william degnan wrote:

>> Recently (today) I noticed Address light 16 would come on when I examine
>> an address.  For example
> All switches down, turn on machine  (set to 000 000)
> RUN/PROC/BUS/CONSOLE lights come one, all other lights off
> address light 16 comes on, RUN/PROC/BUS/CONSOLE lights stay on.
> If I hit START light 16 turns off.
> If I try again, to load an address, the address I selected appears, but so
> does light 16.
> I believe I have seen the explanation for this symptom somewhere, but
> reading the 11/40 CPU manual and handbook and I could not find the
> explanation.  Does anyone know what this means?
I don't believe this has any specific diagnostic meaning.  It's possible 
that there is a stuck bit in the front panel logic.  It's also possible 
there is something wrong with the MMU, since (IIRC) the MMU is what 
drives address bits 16 and 17 from the CPU side.

If you load an address from the front panel, is it *actually* loading 
the address on the switches, or is it loading the address on the 
switches with bit 16 also on?  Try depositing a known word into a 
specific memory address, like 1000 using the console PROM, then try 
reading it back with the front panel.

- Josh

> I have been booting directly into the console, lately the system has no
> problem loading and running from the console.  Perhaps this huge missed
> issue is the root of the problem I have been having get much else done.
> Bill

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