MicroVAX II - TK50 problem

[Pete Turnbull]

On Mar 10 2005, 14:18, willisjo at zianet.com wrote:

> I did know about the serpentine weirdness. It caused me a great deal
of
> grief in getting the system to pass its self tests in the beginning,
before
> I stumbled (quite accidentally) across hamster's digital$resources
> page on Qbus. However, I think you may have hit on something. The
RQDX3 is
> not at the end of the bus.

No, it's not that...

> If memory serves (I'll verify this
> after I get home from work today), the backplane arrangement is
>something like this:
>      A        B        C        D
> +-------------------------------------+
> |                CPU                  |
> +-------------------------------------+
> |                Memory               |
> +-------------------------------------+
> |     TQK50*       |                  |
> +-------------------------------------+
> |     M9047        |                  |
> +-------------------------------------+
> |     RQDX3*       |                  |
> +-------------------------------------+
> |                DHV11                |
> +-------------------------------------+
> |                ???? **              |
> +-------------------------------------+
> |                  |                  |
> +-------------------------------------+
> |                  |                  |
> +-------------------------------------+

That's what's wrong.  Assuming this is in a BA23, you don't have
interrupt or DMA grant continuity.  The first three slots are Q22-CD
but (if this is a BA23) the fourth is Q22-Q22 so you need something in
the RHS (slots C+D) of row four:

     A        B        C        D
+-------------------------------------+
|                CPU                  |
+-------------------------------------+
|                Memory               |
+-------------------------------------+
|     TQK50*       |                  |
+-------------------------------------+
|     M9047        |       RQDX3      |
+-------------------------------------+
|                DHV11                |

That's the only reason you have a grant card; it is to sit next to a
dual-height card in a Q22-Q22 slot.  If this were a BA123, you'd not
need it at all.

-- 
Pete						Peter Turnbull
						Network Manager
						University of York