Quentin wrote:
>
> I was so sure this was discussed before that I've spend the past two
> hours searching the archives at iversoft and piclist.com (search not
> working there).
>
> I am looking for a nifty idea to monitor a single wire bus. The bus is
> floating when idle (no pullup/downs). So I can not just set the PIC I/O
> to input and monitor it. The pic must read the tristate as neither a
> high or a low. IOW, the PIC waits for a high or low.
> This is a hobby project where I want to connect up several PICs on a
> single wire. (I know about I2C and SPI, but that will defeat the whole
> point).

You can't leave the line free floating. Leave it
as a "weak" 5v with say a 10k resistor.
Then any PIC in control can pull it hard to 5v
or 0v, giving you 3 valid states.

Just make sure each pic also has a resistor, say
1k, so you don't get overcurrent situations when
they try to test the line.
-Roman

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