Continuing the "strange ways to signal on 2 wires" theme, for the master,
you could swap line feed polarity as signalling. If slaves have full bridge
power pickup they get 100% power feed at full signalling rate.

In a loop you could extend this to slaves with each swapping power feed
polarity to downstream members until the loop got back to the master.

Polarity swpaiing has the advantages of no pwoer interuption and good speed.

_________

Versions of the 2 wire half duplex and 3 wire full duplex on power supply
wires were implemented by the old Nat Semi "AARTS" of the ?1970's The number
MM14469 (MC14469?) or similar rings a bell but this may be wrong. These
received an address and one or ? two data bytes and responded with a data
byte of their own. Processorless remote serial I/O. Quite easy to implement
with a modern processor.

Yep - just checked my heap database - it is MC14469. Price here was $NZ13.50
in 100s in 1992 so a PIC would easily get under that.



    Russell McMahon

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