Help identifying mystery Unibus board

Jay Jaeger cube1 at
Tue Sep 24 10:52:49 CDT 2019

On 9/24/2019 3:15 AM, Tony Duell via cctalk wrote:
> On Tue, Sep 24, 2019 at 9:13 AM Bill Degnan via cctalk
> <cctalk at> wrote:
>>>> Here's the full board, for reference:
>>>> Thanks,
>>>> Josh
>>> /Mattis
>> You confirmed it is not Omnibus bd, like a drive bootstrap board?
> I think with that many address switches, a 'vector' switch, the grant
> jumpers and the connector at that end it's Unibus.
> -tony

Assuming UNIBUS...

Looking at the address switches, I see 11 selectable bits out of how
many we don't know.

If at one extreme, the bits start at bit 15 (MSB) [assuming bits 16 and
17 are also 1], then the address of the ports on the board would be
77744X - 77747X - that seems like a lot.  (They might start at bit 17,
but then the space used by the board gets absolutely crazy).

If, on the other extreme, we suppose that the top 4 bits are 17 (along
bit bits 17 and 16), then we get 777762 - 777763.  That might actually
be possible.

One might continue the exercise one bit at a time between the two to see
if the address lands anywhere "interesting".

777710	Not here (Conflict with CPU registers)
777620  Unlikely (memory management)

A more sure way would be to find the address line to which the first
address switch corresponds.


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