PDP 11/40 Unibus termination query...

On Thu, May 21, 2009 at 9:06 AM, Tom Uban <uban at ubanproductions.com> wrote: 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. 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. At Software Results, we used to make dual-height grant cards so we could stick one in every COMBOARD box for our customers' convenience (the last batch of 100 we ever bought ran about $20 each, 15 years ago). Since we had them lying around, we always removed *every* NPR wire on every backplane and never used G727 single-height grant cards. It just took too much time to reconfigure machines otherwise. I've also seen shops that tended not to want to buy fistfuls of dual-height grant cards, so they just minimized how often they fiddled with the backplane - once they got it right, they tried not to mess with it. I still have the films (manual paste-up) for the Grantosaurus Rex cards, c. 1981., but our last grant card was a plain rectangular affair with a handle cutout. Not as interesting, but much cheaper to make. -ethan