PDP-11/05-NC with M9301?

Mattis Lind mattislind at gmail.com
Thu Mar 17 10:57:03 CDT 2016

2016-03-17 13:49 GMT+01:00 Noel Chiappa <jnc at mercury.lcs.mit.edu>:

>     > From: Mattis Lind
>     > I was thinking of using a M9301 board to get a console emulator and
>     > some different bootstraps with the 11/05. But can I just put the
> M9301
>     > in the slot where the M930 normally goes?
>     > ...
>     > M9301 goes into MUD slots. But can it go into the slot where a M930
>     > normally sits?
> I haven't personally looked into doing this in detail, so I can't give a
> definitive answer, but your last question here makes alarm bells go off in
> my
> head.
> The M930 is designed to go in UNIBUS In/Out slots. These slots do have
> different wiring from the A/B MUD slots. (For instance, UNIBUS In/Out slots
> have _single_ pins assigned for BG4-7 and NPG, providing 'grant in' or
> 'grant
> out' functionality, depending on if it's an In or Out slot. I don't recall
> offhand what function/signal is on those pins in a MUD slot, but I'm pretty
> sure it's not a grant!)

The BG signals are used for +20V, Parity Detect and "reserved" in a MUD
slot. But these pins are provided through jumpers from the pullup resistors
to the bus and to be installed in a MUD slot these jumpers need to be out.

I am curios about the note saying that these jumpers need to be installed
in a 11/70. Why?  I tried to scan som 11/70 documents but did not find in
what slot the M9301/M9312 should go. Maybe it sits in the last slot on the
Unibus and that is why it need to have these jumpers installed?

> I would be fairly astonished if a device intended for a MUD slot would work
> in a UNIBUS In/Out slot, and vice versa.

>From the schematics I get that there is no real difference between M930 and
M9301 unibus wise if the jumpers are out. And thinking of this a bit more
these jumpers should be out unless I install it as the last terminator on
the bus. It makes no real sense to terminate the BG signals close to the

The M930 is grounding some more pins. That's about it. I will go home and
do some measurements on slot 4 AB to see how it is connected.


>         Noel

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