jnc at mercury.lcs.mit.edu
Mon Feb 8 16:04:51 CST 2016
> 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.
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