> Sometimes, protection diodes are a PITA! :)

The 'protection diodes' figured in my drawing are in fact the inherent
bulk reverse diodes in the CMOS output transistors. And there is no way to
buy cmos chips that haven't got them. Had the circuits been open drain
(which the pic isn't) then the problem would have been inexistent. But the
PIC has only one open drain pin per chip afaik. Unfortunately the low Vil
for I2C precludes the use of shottky diodes between the controller and the
slave. Afair I2C wants 0.9V Vil (why so low when this destroys noise
immunity ?).

Peter

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