Hi Christian.

>This was my knowledge, too, befor i've seen this kind of bus. Maybe it's
not
>really a current loop, but the construction seem's to be.
>I've found a trasistor for TX (pulling one line down to gnd) and on the
>other side a optocoupler to receive the signal. This seems to be a classic
>current-loop. But i found also they just connect some receivers on the line
>and do not daisy chain it.

>I think the construction should work in this way to lit/drive just more
than
>one led (opto coupler) as in a classic current-loop. But with every
receiver
>(opto coupler) the current will raise.

Yes, this sort of thing does exist - in fact, most vending machines use
exactly this setup for polling cash acceptance devices such as coin changers
and bill accepters. The most common standard in vending machines these days
is MDB (in Europe and Australia anyway) which describes both the physical
implementation and protocol specs. I have a hard copy but unfortunately do
not have an electronic version to send you. It works in a classic 1-master,
multiple-slaves fashion, but in reality it is very rare to use more than 2
or 3 slaves.Do a web search for MDB or visit a few vending sites (Coin
Acceptors, Mars Electronics International, etc.) and you should find
valuable info.

Regards, Kresho.

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