PDP 11/40 Unibus termination query... - test-drb@ccmp.vtda.org

21 May 2009

Ethan Dicks <ethan.dicks at gmail.com> wrote:

...
  On Thu, May 21, 2009 at 9:06 AM, Tom Uban <uban at
ubanproductions.com> wrote:
 > >> I'll check the NPG jumpers --
here's a stupid question -- how do I find
> >> where they're supposed to be? ?I've looked all over for a simple
diagram
> >> showing which pins are CA1 and CB1, but I'm not finding them...
 >
 > The backplane information is clearly described in the Peripherals Handbook.
 > If you don't have a copy and you intend to work with these machines, then
 > you need to get yourself a copy.  
 Having worked with these machines a lot over the years, I can
 personally recommend having the right handbooks on hand when
 configuring things or diagnosing problems - it will save a lot of time
 and grief.  Back in the day, we always had them and we used them
 frequently.

  > The 'C' in CXX is the slot... 

 Another way to see is to look at a dual-height Unibus grant card and
 note which pair of pins is shorted together on the "C" finger (the one
 that only has one pair of pins shorted, not the one that has 3 pairs
 of pins shorted).  If you don't _have_ a dual-height grant card, you
 are going to have to get very familiar with where the NPR pins are
 because you are going to be wrapping and unwrapping that jumper on the
 backplane every time you insert or remove cards. 
Those dual height grant cards are excellent for people who aren't overly 
sure and experienced with this, since they are hard to insert the wrong 
way as well. So you both can check which pins should be shorted, and you 
don't have to fiddle with the NPG line. It is also not totally uncommon 
for people to also insert the grant cards reversed...

But you don't need to remove the NPG wire every time you insert a card. 
You only need to do it for cards that do DMA.

By the way, Tom Uban made a great ascii chart of a backplane slot. That 
should be useful for lots of people who play with DEC equipment, for the 
same notation is used on all older DEC backplanes, not only Unibus.

It's actually this backplane format that defines a flip chip. (Most 
people errounosly seem to think that the bus grant cards are called flip 
chip, they are just one example of a flip chip.)

	Johnny

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