PDP 11/40 Unibus termination query...
derschjo at mail.msu.edu
Tue May 19 22:25:49 CDT 2009
Hey all --
I'm one step closer to bringing my 11/40 back to life -- the front panel
is now responding and I can examine and deposit memory.
But the machine is only responsive without the Unibus terminator (an
M9302) installed. If it's installed, the front panel is basically hung
-- toggling "Start" causes a brief flurry of activity, but that's the
only thing that causes any response.
Without the terminator installed, the front panel more or less works, I
can examine and deposit memory, load the address register, etc... but I
can't get any toggled in code to run, obviously -- it traps to the bus
error vector at 00004.
(There's also an odd issue, which I doubt is related, but
Examining/Depositing does not correctly increment the address --
starting from 0, it's "0, 2, 6, 12, 16, 22, 26..." and if I start at 1
it's "1, 3, 7, 13, 17, 23, 27...")
I currently have the CPU boards + MMU option installed in the correct
order with a SLU card in the SPC slot, and an M981 connecting to a
4-slot Unibus backplane with a single 64K MOS memory card (M7891) in
slot 2 -- all other slots have grant continuity cards installed. The
Unibus terminator is installed in the last slot.
Thanks as always,
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