> From: Jason Thorpe <thorpej@nas.nasa.gov>
> Date: Thu, 02 Feb 1995 17:39:11 -0800

> Folks -
> 
> I have this quasi-dead 3/260 sitting in a machine room downstairs from my 
> office.  It has what appears to be a dead frame buffer.  Pulling that 
> board resulted in it happily talking to a serial console whilst in diag 
> mode.  Unfortunately, every attempt to talk to any device on the VME (as 
> opposed to the main board) results in a bus timeout.  So, it appears that 
> I need to reconfigure the backplane.

For VME in general, empty slots require some jumpers.

Also, Sun memory boards are unusual in that they do not
pass through the Bus-grand and I-ack signals, so you need
to put jumpers on any slots containing Sun memory boards.

When jumpering an empty slot (or Sun memory board slot) you can
get by with just a couple of them (I forget which) but I always
just install all four jumpers on a slot that needs any jumpers.

Oh, by the way, in the Sun backplane, not all slots are the same!
Some have the VSB bus wired on P2 (lower connector) and some do not.
The SCSI controller, for example, has the SCSI bus wired to the P2
connector, and it REALLY doesn't like trying to drive the VSB bus.
So, SCSI boards (or other P2 users) can only go in slots 7,8,9.

So as for placement, the typical Sun3/260 has the following:

Slot	Jumper	What's there
1	N/A	CPU
2	IN	empty
3	IN	empty
5	IN	RAM board
6	IN	RAM board

7	OUT	SCSI
8	IN	empty
9	IN	empty

10	OUT	Graphics board
11	OUT	empty
12	OUT	empty

Jumpers don't matter beyond the highest slot with a board installed.