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

Guy Sotomayor Jr ggs at
Tue Nov 22 21:41:16 CST 2016

> On Nov 22, 2016, at 5:43 PM, william degnan <billdegnan at> wrote:
> 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.

Hmm.  I just realized that folks are having trouble booting an 11/40 from an
RL02.  My 11/40 (which is a *big* configuration) has an RL11 in addition to
the RK11D and in the past I’ve booted it from an RL02 with no problems.  So
I suspect it’s some sort of Unibus configuration issue.  I haven’t fired up
the system since I moved it a few years ago so it would likely take a bit to
check things out.

TTFN - Guy

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