Strange third party board in PDP-11/45

Mattis Lind mattislind at
Mon Jul 23 01:36:28 CDT 2018

> Studying the MS11 Maint Manual, the MS11 controller has access to the full
> address and data from both the CPU (FastBus) and UNIBUS B. (The FastBus
> actually has two uni-directional data busses; in and out.) So all that
> info,
> this hypothetical cache board can get from the slot it is plugged into
> (assuming the cache is plugged into one of the controller slots), over its
> connector pins.
> The connectors on the back of the card, and two small boards, must be for
> listening to UNIBUS A (in configurations in which the two UNIBI aren't
> joined
> together)? (I'm too lazy to check the slot numbers are see what they
> actually
> are.)
> And there is indeed a signal which the MS11 uses to tell the CPU it has the
> location the CPU is asking for, so it's theoretically possible to build a
> cache
> card that plugs into a FastBus slot.

Here is how it is connected:

The sandwiched dual boards are i sitting in 27 / 26 AB. The board in 27AB
was empty (quick glance), while the board in 26AB has a few TTL chips on it.
 Slot 26AB is the Unibus A slot, Slot 27 AB should be a terminator on
Unibus B. (maybe there were terminating resistors on the second board.
Didn't check in detail) Slot 28AB is Unibus B and goes to the DD11-C and
the RK11-D backplanes.

The hex ABLE/ ACT board sits in slot 21 which is the memory controller
board for the MS11.

It very much looks like it is a Cache board. But why have some one written
"Not used" (Används ej) on it? I'll hope I find the documentation for it!


>          Noel

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