UNIBUS extension card/cable sets

Paul Koning paulkoning at comcast.net
Thu Jun 25 13:06:46 CDT 2015

> On Jun 25, 2015, at 2:01 PM, Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:
>> 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).

What’s between the backplanes?  If it’s a repeater, that would be correct (because you have two separate transmission lines).  If it’s a cable, then this is wrong.  But as Tony said, it might be that it’s not so wrong that things break, thanks to the small scale and slow speed of Qbus.


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