brew-your-own-unibus boards?

From: der Mouse <mouse_at_Rodents.Montreal.QC.CA>
Date: Mon Jan 19 23:30:49 2004

> For me, at least, the hard part of designing a modern Qbus and/or
> Unibus interface would be what to select for bus drivers.

Well, for Qbus...there's an appendix in the KA630 document that's
titled "Q22-Bus Specification". Based on that:

>From the looks of it, for a driver you can use almost any
open-collector TTL output - at least, a quick look at the specs doesn't
reveal anything that stands out as incompatible.

The receivers are a bit more interesting. The spec says that their
threshold must be between 1.3 and 1.7 volts and that their high-level
input current must be no greater than 80?A; it fails to give any limits
on how much current they source into a low-level input, though there
surely must be such a limit. Are there any bus receiver chips that
have a reference-voltage pin, which could be connected to (say) 1.5V?
Basically, a bunch of specialized voltage comparators?

Personally, I'd be tempted to just use TTL and see if it works (LSTTL,
probably, since that sources less current into low-level inputs). But
of course "it works for me" isn't good enough if you're designing for
other people's use.

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Received on Mon Jan 19 2004 - 23:30:49 GMT