PDP-11/05-NC with M9301?

Guy Sotomayor ggs at shiresoft.com
Thu Mar 17 11:27:42 CDT 2016

> On Mar 17, 2016, at 6:01 AM, Mattis Lind <mattislind at gmail.com> wrote:
> If one read notes in the PDP-11/04 printset it says: Do not insert a M930
> or M9302 in a MUD slot. Only in the Unibus slots or you will have short
> circuit. On the other hand it does not say that the M9301 (or M9312) cannot
> be installed in a unibus slot. It recommends that those boards go into MUD
> slots. But electrically I cannot see that it shouldn't work. Especially if
> you jumper W1 - W5.

Hopefully this will clarify a few things:
“Unibus”: These are the AB connectors in the *last* position of a backplane.
It allows for bridging between backplanes.  The only “card” that can go these
“slots” is a terminator (ie M930) or a terminator bootstrap (ie M9312).

SPC: These are the CDEF connectors in any of the slots of a “unibus” backplane.
Not all backplanes support SPC slots.

MUD: These are the AB connectors in some newer backplanes (usually associated with
the extra slots in a CPU backplane…11/34 and 11/04 CPUs have MUD slots).  MUD
stands for “Modified Unibus Device”.  They are *not* compatible with Unibus slots
as they have different voltages present than what are on the Unibus slots.  You *will*
“blow out” a board by plugging something designed for a Unibus slot into a MUD

TTFN - Guy

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