QBus termination?

[Paul Koning]

>>>>> "joe" == joe heck <joeheck at splab.cas.neu.edu> writes:

 joe> The "definitive requirement" I suppose is that a bus is a
 joe> transmission line and is modelled like one.  That means that it
 joe> should (in this instance) be terminated on each end. ...

 joe> In reality, I rarely paid attention to termination when using a
 joe> single backplane. ... Yes, I have regularly broken the rules.
 joe> Things still worked.

Sure.

The transmission line nature of things matters if the total wire
length is more than a small fraction of the wavelength of the highest
frequency signal you care about.  Qbus rise time is specified as 10
ns, which translates to about 6 feet.  So for a single backplane the
reflections aren't going to mess up the pulse shapes much.  You'd
still get ringing and overshoot, but no excess jitter.  And on a small
config there would be lots of margin.  So yes, you can get away with
various forms of abuse...

Re too many terminators -- I still have a copy of an article (in "RSTS
Professional") that showed an Ethernet with a terminator in the
middle.  They were showing how to convert thick to thin, and did that
with a T connector complete with terminator...

     paul