Phil wrote:
> What would you suggest for serial communications between PIC's
> (16F877/876's) that are located about 200 feet (60 meters) apart and
> on Cat 3 (or if I am lucky Cat 5) cable?  The data rate is slow, much
> less than 1,000 bps.  I have looked at I2C but it appears to be
> limited to only a few meters.  Did I miss something in the spec that
> allows it to operate at longer distances and reduced data rates?
>
> I would prefer a "daisy-chain" interconnect but if necessary a star
> topology could be implemented.
>
> Is it time for a roll-your-own interface?  Currently I am not I/O
> limited but that may change :~)
>
> Data, Clk and Vss would seem to be the easiest and minimum number of
> signals.>   Your thoughts and suggestions are appreciated.
>
> Phil

If minimum wires is the goal, perhaps you could emulate the Dallas
1-wire protocol, it only takes two wires.  The Master end is pretty
easy, but the Slave implementation might be a little harder.  Devices
taking turns being the Master and Slave would even be trickier, but IMO
it could be done with some careful planning.  The layout would
physically be like a daisy chain running from device to device, but the
functionality would be more like a star since all receivers can "hear"
the transmission.

Of course someone else will probably recommend something allot more
practical like RS-485 multidrop.  ;-)

michael brown

"In the land of the blind, he who has one eye is king"

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