I'm looking at a project that will have several (4-8) PICs in the circuit.
They need low bandwidth (~100 bytes/sec) communication between each node
and the main controller. The problem is they need galvanic isolation, there
could be a couple hundred volts difference between them. Main PIC will
probably be a 16F877 handling front panel details (character LCD and
buttons) as well as connection to host PC, nodes will probably be 12F675s
or 16F676s.

They'll be within a few inches of each other, and there shouldn't be any
significant 'noise' to overcome. The USART on the main controller is
already committed and I have to avoid using the interrupts on the nodes (I
already have several processes happening there) And I'd like to avoid
crystals/resonators on the nodes if possible. (cost, complexity, not needed
for main task anyway) So I think typical RS232 is out.

I was thinking of perhaps a clocked serial similar to a shift register. One
pin on the central controller for data in, one for data out, and one per
node for clock.

Doable, but I was hoping for a more elegant solution. Any suggestions?

Thanks,
-Denny

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