VIPA Crate Notes
                      --------------------

                                           Original Version  19-APR-1999
                                           Most Recent Ver.  20-APR-1999


Gaining Bus Mastership
20-APR-1999

There have been various problem with modules being able to gain Bus Mastership
in the VIPA crates that we have used.  Sometime this involver the module not
being in Slot #1 and sometimes there is something more complicated going on.
This is note about various modules that we have tried to use as Bus Master in
VIPA crates.

   MVME-133A20   This 68k cpu module appears to have no problem becoming
   Bus Master no matter what slot it is in.  For example if it is the only
   Crate Controller in the VIPA Crate and it is in Slot #2 everything works
   with no problems.  But note that with a VIPA crate it is NOT ok to run
   the 68k board as the crate controller and have it in any slot except
   Slot #1.

   Vertical Interconnect Slave   If one of these is going to be Crate
   Controller then it appears to work only if it has its MAZAR chip installed
   and is in Slot #1.  If a VI Slave is going to request Bus Mastership
   from another Bus Arbiter then it must be set as NOT crate control,
   can be in any slot except Slot #1, and can have its MAZAR chip installed
   or removed.

   Bit-3 Cards.  Although there was some early confusion about problems with
   these cards and funny pull up resistor boards and such the the following is
   now clear.  With a VIPA Crate, if a BIT-3 card is going to be Crate
   Controller then it must be in slot #1.

The VIPA Crate uses 74ACT32 gates to daisy chain the Bus-Grant signals
from slot to slot.  The BG_IN and BG_OUT from slot #N go to the two
inputs of a 74ACT32 and the output of this "OR" gate goes to the BG_IN
of slot "N+1".  At each slot there is a 82k Ohm pull down resistor
from BG_OUT to ground.  Only at slot #1 there is also a 82k Ohm pull
down from BG_IN to ground.

So, unlike normal VME crates, if we put the Bus Arbiter in any slot
except slot #1 then both the Arbiter and the 74ACT32 will try to drive
the BG_IN to that slot.



Power Bus Connections to Use for -5V and -2V
20-APR-1999

So far all I know is that for the SCL Hub-End the -5 Volts will
involve the Vw - Rwx connections and the -2 Volts will involve the Vz
and Ryz connections.