When the backplane is jumpered for Passive terminator operation you should
see about 5 Ohms between +5V and Ground. (A 330 Ohm pull-up and a 470 Ohm
pull-down at both ends of each signal line)

When the backplane is jumpered for Active termination the 330 Ohm and 470
Ohm terminators are put in parallel and then connected to the output of an
Op-Amp. The Op-Amp has a 330/470 voltage divider as a voltage reference.
This will make 2.95V going through a 192 Ohm terminator at both ends of
each signal. You should see about 800 Ohms between +5V and Ground when it
is jumpered for Active termination.

For a short backplane like the four slot Passive termination should work fine.

There is a document called the "VME Technical Manual" available from
Pentair Electronic Packaging (the USA distributors of Schroff products)
that describes in detail the operation of the VME backplanes.

If you can't get the backplane to work you can send it to me and I will run
it through a full production line test.

At 04:48 PM 8/11/01 GMT, Ken Seefried wrote:
>
>Over the last few months, I've put together a batch of VME gear to run 
>NetBSD on (2xMVME164, Heurikon Nitro260, possibly an MVME177, memory cards, 
>SMD controllers, SCSI controllers, racks, etc.).  I also picked up two new 
>(supposedly) Schroff 4-slot VME backplanes (model 23000-464); very 
>impressive physical construction.  Unfortunately, I'm having some problems 
>with them.  It's probably because of my ignorance of VME, and the slim doco 
>they came with. 
>
>Basicly, I've got them in a rack with another, known-working, non-Schroff 
>backplane.  When I apply power (+5v & GND) to the Schroff backplanes, they 
>short the power supply (or rather, the PS detects the short an doesn't come 
>on line).  Using an Ohmmeter confirms that +5v to GND has no resistance.  
>The known working backplane has about 5 ohms between +5v & GND. 
>
>Now, there are 4 3-pin jumper headers on the board, with 1-2 labeled A & 2-3 
>labled P.  All are straped to P.  There is also a 5-pin header labeled from 
>the top SYSRES, SYSFAIL, ACFAIL, +5V, GND.  Nothing is attached to this 
>header. 
>
>So...any clue what I've done wrong, or did I get a pair of duds? 
>
>Many thanks... 
>
>Ken 
>
>
Michael Thompson
m_thompson@NOSPAMids.net