ISO: PDP-11/40 LTC and Stack Limit options

william degnan billdegnan at
Tue Nov 22 19:43:56 CST 2016

On Tue, Nov 22, 2016 at 8:13 PM, Guy Sotomayor Jr <ggs at> wrote:

> > On Nov 22, 2016, at 4:40 PM, Josh Dersch <derschjo at> wrote:
> >
> >
> > So... maybe I just completely missed the memo on this, and maybe there's
> still something wrong with my backplane... is it possible that slot 9 of
> the 11/40's CPU backplane is wired *specifically* for an M7800?  I guess I
> need to spend some time tonight seeing what the differences are... but now
> I need to go attend to a cranky 2yo who just woke up from a nap…
> >
> I seem to recall something similar with one of the 11/40’s I was working
> on.  I believe that because the 11/40 CPU backplane is wired for an M787
> that things don’t work quite right if you try and install an M7856 into the
> SPC slot in the backplane and try and use it and not the M787.  There is a
> way to jumper the CPU backplane so you can use na M7856 and not the M787.
> I haven’t really investigated it in detail (and it’s been a long time since
> I messed around with the 11/40 at that level).
> TTFN - Guy
I have my 11/40 fired up right now too.  I can load BASIC and I have a
M9312 with a M7800 that returns serial signals/monitor running.  I have the
CPU backplane, two core planes (empty), a DD11B and an DD11C.   I can
operate without a grant card in slot, but I can't boot up using RL02 either
way, still trying to track down if I have a UNIBUS issue.

If there is something I can measure for you, for comparison purposes, let
me know.  I will be around tomorrow too during the day.  I live near Phila,
it's 845PM Tuesday at the moment here.


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