On Thu, 25 Sep 2003, Thor Lancelot Simon wrote:

> On Thu, Sep 25, 2003 at 12:37:19PM -0500, Gunther Schadow wrote:
> > Johnny Billquist wrote:
> > >To make a short answer: the unibus termination is *vital*.
> > >If you fail diagnostics with it inserted, it's not because of the
> > >termination, but because some problem in your Unibus don't show up
> > >otherwise. The termination should be in the last slot, in AB.
> > 
> > So, I need grants and NPG grants in front of the terminator?
> 
> *every* slot on the Unibus must have either:
> 
> 1) A card
> 2) A continuity ("grant") card
> 3) if a slot that is wired for VAX DMA, a VAX DMA card or a *VAX DMA
>    continuity card*.
> 4) A terminator
> 
> The terminator must go in the last slot.

Almost all points here. The terminator should not be in that group,
though. The terminator is located at another place than the interrupt
grant lines (which the small bus grant card have) and the NPG line, which
the extended grand card have (which, btw, is not VAX-specific in any way).

Slot 1 and 9 (on a 9 slot Unibus backplane) are "old" Unibus, while the
other slots normally are MUD slots. There are some differences, but it
don't normally matter much. Also, slot 1 and 9 can only hold quad size
cards, while the others can take hex size (for obvious reasons).

	Johnny

Johnny Billquist                  || "I'm on a bus
                                  ||  on a psychedelic trip
email: bqt@update.uu.se           ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol