Howard Winter wrote:
> True, but this was solved nearly thirty years ago by Datapoint in
> developing and implementing ARC (later "ARCnet"), when Ethernet and
> Cambridge Ring (the computer-, not spy- network :-) were still research
> projects. It is true peer-to-peer, with physical multiple-star layout
> but logical sequential token-passing.  It has a "who's there" process
> which means that each node learns who is either side of it, and it's
> triggered either by a new node appearing or an existing one
> disappearing.  There is no noticeable slowing down when this happens.
> We were using it in a live environment in the late seventies.

I agree this is all possible.  I was just trying to get Neil to realize that
while RS-485 can be made to do what he wants, there are a lot of sticky
details that are going to make a robust implementation tricky, or at least a
lot more work than he seems to think.

Your approach is a good example of that.  How long did it take how many
people to develop this?  Certainly it could all be done in a PIC using
RS-485, but I would hardly classify that as the "simple" Neil thought it
would be.

> I remember the day when someone mentioned that they couldn't "see" any
> of the equipment on the far side of the site (there was a canal running
> through the middle of the factory, with a bridge that carried the
> cables and pedestrians across) and it turned out someone had cut
> through a great wad of cables, having been told they were disused.  One
> of them, ours, wasn't!  The system carried on happily in two halves,
> and since the cross-canal requirement was only used a few times a day,
> nobody noticed for some time!  As soon as the culprit cable had been
> identified and re-made, it all reconfigured itself back as it had been.

Very interesting.


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