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Experimental Physics and
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<== Date ==> <== Thread ==>

Subject: VME bus confusion
From: winans@aps.anl.gov
Date: Thu, 25 May 95 16:02:46 -0500
Hello VME-bus users.

In the last month, Jim K. and I have counted 4 seperate cases where
we were personally contacted due to a situation that caused lost due to
improperly configured VME hardware.

Please read and remember these simple important tips:

1) There MUST ALWAYS be a board of some kind in EVERY slot of the VME
   crate starting on the left and working right.  If you MUST have
   a missing board, you may simulate it by installing the BG and IACK
   jumpers often found on the VME backplane.

   Failure to follow this rule causes very strange things to happen. 
   Common sense does not seem to apply to this easier... don't think
   that just because a board does not generate IRQs or operate as a bus
   master that things will still be OK.  We have seen otherwise!

2) Don't leave the backplane jumpers installed in a slot where you have
   a board installed.  This is essentially the inverse problem of #1
   above.  If the manufacturer requires they be installed, send the
   board back and tell them that they should hire a EE that has
   actually seen the Rev C.1 VME spec to design their boards from now
   on.


One last and perhaps the most important piece of information:

    If anyone ever calls me again with a problem that is caused by
    this... the service charge will be a 6-pack of Miller Highlife in
    bottles.  Viva le Champaign of Beers!


--John

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