John Wilson <wilson@dbit.dbit.com> wrote:
> However the MSCP spec requires that unit numbers be unique on the
> *system*, not just within the controller; so once you add the second MSCP
> controller the port-unit matchups stop working. Seems like an annoying
> rule though, all other types of disk/tape units only have to be unique
> within the controller.
   I hope that you have really meant "SDI" where you have written "MSCP".
(See my lengthy posting of 20-DEC-1997 for a description of the differences
between the two). If this applied to all MSCP controllers, the universe
would look completely different from the way it does. Suppose I have two
RQDX3s in a MicroVAX (I can do that, right?). I can have 4 MFM disks on
each, giving me a total of 8, right? On each RQDX3 the 4 MFM disks can't be
numbered anything other than 0-3, right? The jumpers on the drives don't go
beyond 3, and they don't matter anyway since the unit number is determined
by the position of the control and data cables on the MFM signal
distribution board, right? Then the drives on the first RQDX3 will be
called DUA0-DUA3 and the ones on the second RQDX3 will be called DUB0-DUB3,
right? And you are saying that it's impossible, right? Or are you saying
that the second RQDX3 will automagically detect that it's secondary and
bump all unit numbers up by 4? But how can it detect that it's secondary?
   Would you please clarify this?
   
   Sincerely,
   Michael Sokolov
   Phone: 440-449-0299
   ARPA Internet SMTP mail: mxs46@po.cwru.edu
   
   P.S. You were referring to "the MSCP spec". What have you really meant
by that and where have you got it?