ISO: PDP-11/40 LTC and Stack Limit options
derschjo at gmail.com
Tue Nov 22 18:40:56 CST 2016
On 11/22/16 4:00 PM, Josh Dersch wrote:
> On 11/22/16 9:27 AM, Noel Chiappa wrote:
>> > From: Josh Dersch derschjo at gmail.com
>> > see if the same is true for other bus grants -- I can run the
>> > with no grant continuity card at all in slot 9 and everything
>> Well, the BG4-BG7 grants definitely _are_ run through the SPC slot 9
>> below) - at least, on a stock system. It's _possible_ that the software
>> you're loading doesn't use interrupts. (I have this vague memory
>> that, unlike
>> the -11/34, the /40 doesn't complain if there's a non-continuous
>> grant line.)
>> Or perhaps someone wired them across on that slot, to avoid
>> trying to put a G727 down there.
> Yes, I'd expect them to be run through the slot (though I expected the
> NPG, too :)). And there does seem to be continuity between the BG
> pins on the CPU backplane and those on the DD11.
> If I remove the grant continuity card from slot 9, I can still boot
> XXDP. If I remove a grant continuity card from the DD11 (with NPG
> still intact), I can't -- it hangs as I'd expect with a hole in the
> grant chain.
> No one's done anything cute like hard-wiring the grants in and there's
> no evidence of any modifications. All expected voltages are present
> on the backplane pins in the right places. I put a little contact
> cleaner in the slot too, just in case. I still can't get an SLU to
> function in that slot, though the CSR addresses seem to respond and
> the console/diagnostic PROM chugs along happily when I power the
> machine up (though nothing appears on the serial line).
> Tonight I may try running the SLU on an extender board and verifying
> that all the proper voltages are actually making it to the board. The
> fact that the board appears to be responding but I'm getting nothing
> over the serial line makes me think that maybe the -15V isn't present
> for some reason...
Annnnd: mystery solved (?). I had borrowed the SLU I was using in the
11/40 from my 11/34. This was an M7856 (DL11-W). Thought I'd grab
another SLU from my UNIBUS drawer and configure it up so I could put the
7856 back in the 11/34, but all I had left were the older, more annoying
to configure M7800s (DL11-D). So I jumpered it up (max of 2400 baud
with the crystal that's currently installed, blah) and installed it.
Works fine in the DD11 backplane.
Moved it to slot 9 of the CPU backplane. Still works.
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...
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