DEC bus transceivers

[Noel Chiappa]

    > From: Guy Sotomayor

    > Secondary chip marke[t] (only reputable vendors). 

I'm a little more willing than Guy to troll in disreputable waters (I bought
1K DS8641's from a source in Hong Kong), so I have this:

  http://ana-3.lcs.mit.edu/~jnc/tech/QSIC/TestCardF.jpg

which has a bunch of special circuits on it to test chips to make sure they
meet specs; e.g. the large potentiometer is so I can vary the input voltage
to see where it switches from 0 to 1, etc.


    > From: Paul Koning

    > it would be odd to have one; I can't think of anyone who would expect a
    > PDP11 to work with part of its devices powered down. For one thing, if
    > the box with the terminator loses power

Forget the terminator - as Jon Elson also points out (his email appeared
while I was creating this one), any device which uses interrupts, if
un-powered, won't pass grants.


    > From: allison

    > Bottom line is someday there will be no DEC parts and what then? I
    > reserve DEC parts for repairing defunct boards for new and unique build
    > it would be a waste of scarce material. 

For actual DEC interface IC's like DC003's, sure. Those are hyper-rare.

But DS8641's are available in the 10's of thousands, there's no earthly way
we could use them all on repairs. Yes, when they run out, we'll have a
problem - but I plan to cross than bridge _if_ and when we get to it.

	Noel