UniProbe - Standard UNIBUS, Modified UNIBUS

Parent Category: Tools Category: UniProbe - an UNIBUS signal adapter Written by Administrator

There are 2 different "UNIBUS" connectors on PDP-11 backplanes.

The "Standard UNIBUS" slot typical sits at the edge of backplanes, and is used to connect backplanes via UNIBUS BC11 white flat cable, or hold an terminator.


The "Modified UNIBUS" ("ModUB") often occupies Slot A and B of the hex socket which have an SPC in slots C to F.
It is optimized to hold memory cards and differs from the Standard UNIBUS:

Putting a standard UNIBUS card into a "ModUB" socket may cause major damage, as the >15V voltages are routed to signal wires then.
See the BIG warning label on the M9302 card!



Signal differences between Standard and Modified UNIBUS are (from the 11/34 system manual):

stdub modub

UniProbe can be build for either Standard or (exclusive or!) Modified UNIBUS sockets.
If build for ModUB:


Building UniProbe for the 4-row SPC socket would also have been a good idea.

However there are situtations where the SPC slot is not available.

Prefering the UNIBUS slot over SPC is in fact a decision for flexibility and against comfort.