UNIBUS extension card/cable sets

Noel Chiappa jnc at mercury.lcs.mit.edu
Thu Jun 25 13:01:29 CDT 2015

    > From: Paul Koning

    >> Right, but the very similar QBUS does have terminations (of a sort -
    >> the rules for when you need terminations on QBUS extensions are so
    >> complex that I don't really grok them yet) 'in the middle'

    > That doesn't seem likely. ... the definition of 'termination' is
    > something that you learn in EE 101 and are unlikely to forget.

I agree with your sentiments, _but_ all I know is that if you look at,
e.g. the 1982 'microcomputers and memories' handbook, pg. 251, you'l see a
three-backplane system, with terminations at the start _and_ end of the first
backplane (and also at the end of the third backplane).

I've seen other similar diagrams elsewhere, that's merely the first one I ran
across in a quick search for this post. Like I said, I cheerfully admit that I
don't really fully understand what's going on there in the analog domain, but
I've seen this in more than one place in the DEC QBUS multi-backplane
configuration instructions.


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