Subject: Re: VS II/RC pieces + Q-bus question
To: David Evans <>
From: Michael Kukat <>
List: port-vax
Date: 02/01/2000 23:24:54
Hi !

On Tue, 1 Feb 2000, David Evans wrote:
> > If I don't put the
> > boards side-by-side, do I need a bus-grant-continuity card?
> > 
>   It depends.  :)  The bus zig-zags.  On the BA123 it leaves the last Q/CD
> slot, then goes to the next slot at the top, then to the bottom, then to the
> next slot to the left on the *bottom*, then to the top, then to the next slot
> to the left on the *top*, then to the bottom, and so on.  So you may or may
> not need a grant continuity card, depending on where you're putting things.
>   It's been nine years since I've looked inside a BA23 so I can't help you
> there.

I don't know exactly, but i think the BA23 backplane has the same ZigZag bus
as the BA123. Only difference: The BA23 only has 3 Q/CD slots. These aren't
labeled so nice. I just crept under my table and picked up my MicroVAX II. This
is not the pure BA23 version, it's the 19" enclosure, but this should be the
same. The upper 3 slots are Q/CD, the other 5 slots are Q/Q. According to my
card layout (where the hell is my tape controller ?), it starts below the
Q/CD slots with the left side, then right, next slot right-left, left-right
and so on. In case of doubt, just try to keep dual-height cards in pairs in
the slots. And attention: The RQDX3 seems not to correctly handle bus grant
and should be inserted as the last card.


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