> Does someone know how to arbitrate  collisions
> in a serial bus easily?

I don't know the proper name, but the principle is that each node has a
number. During arbitration each station that wants to send puts his
number on the bus, but it looses when the (open-collector type) bus does
not show the bit it is putting on the bus. This ensures arbitration
between N stations in log(N) bits. Add rotation to achieve fairness,
when needed. I'm not sure whether you will call this simple....

Wouter van Ooijen

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Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products

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