From: Guy Sotomayor
The reality is that an SPC board will be more
expensive because of the
gold edge fingers.
Oh, right, forgot about that. Yeah, six of one...
I was originally thinking that if I do have to split
the board up, that
I'd make them completely independent. But that has the issue of
requiring 2x the number of UNIBUS transceiver parts (which are all but
unobtainium as of now).
Actually, 8641's (at least) are still around for not much. See below.
some of the signals I'm running are pretty fast
between the FPGA and
some of the other components ... I wouldn't want to run those signals
very far and certainly not across any sort of cabling.
For sure. We've been having issues (although we think we have it licked now)
with signals running across a flat cable between the prototype QSIC's
mother-card (a QBUS wire-wrap card) and its daughter-card (an bought-in FPGA
devel card), and that's for much slower signals (the only thing on the
mother-card are QBUS transceivers and level converters). Of course, the fact
that the interface doesn't put a ground wire between each pair signals wires
doesn't help! :-)
From: Ethan Dicks
I'm starting to get sorry I sold off my surplus
NS8641s from Software
Results 20 years ago. To be fair, I did get over $4 each for them, so at the
time, it was a good deal for me (ISTR retail was $7.50 even then, so I
got a good spread on the price).
I do have some left, but handfuls, not armloads.
NS8641's are still available. I got a bunch from a guy in Hong Kong for
US$1.50 each - considering the source, I built a test card to make sure they
met specs, and they do, so I'm pretty sure they aren't counterfeits. :-)
When I was worried he couldn't find enough, I checked with a supplier (4 Star
Electronics, I think) and they had like 50K available, and quoted me a price
in about the same region, so I don't think UNIBUS transceivers actually are a
problem, at least, not at the moment.