Subject: Re: mvme147 problems...
To: Frederick W. Koehler IV (Joe College) <>
From: Michael Thompson <>
List: port-mvme68k
Date: 08/17/1998 08:36:54
At 02:25 AM 8/17/98 +0000, Frederick W. Koehler IV (Joe College) wrote:
>One question--I have a six slot backplane, and currently have the
>mvme147 in the same slot the original mvme132 68020 board was in.  There
>are two empty slots and then the remaining three slots are filled with
>the tape controller, six port serial board, and finally the winchester
>controller.  In between each slot there are a series of jumpers,
>however, there doesn't appear to be a set of jumpers for each slot, only
>in the spaces between slots.  This leads me to wonder how exactly the
>backplane is to be jumpered.  Should I have jumpers on each side of the
>empty slots?  Maybe the hangs I'm getting at iot;t time are from vmebus
>jumpering problems...  

The jumpers on the backplane are for Bus Grant and Interrupt Acknowlege.
Some VMEbus boards, like disk controllers, do their own VMEbus I/O instead
of using DMA from the CPU. The I/O board requests control of the VMEbus,
the arbiter on the CPU board releases control of the VMEbus, and then the
arbiter on the CPU sends a Bus Grant signal down the backplane.

There are only 4 Bus Grant levels, and you can have several boards, on
the same Bus Grant level. The Bus Grant signal daisy-chains down the
backplane through each I/O board. If you have an empty slot you break
the daisy-chain.

Backplane manufacturers put jumper pins next to the connectors so you can
jumper across empty slots. Unfortunately the jumpers may be to the right
or left of a slot depending on the manufacturer.

You may also find that some VMEbus boards don't pass on daisy-chain signals
that they don't use. This means that you may have to leave jumpers on
even when a board is in a slot.

If the boards are side-by-side without an empty slot between the CPU and the
VMEbus boards you may not need any jumpers. That might be worth a try.

Michael Thompson