Put resisters inline, and then diodes going to the power supply (+5 or
+3.3).  The resisters limit the current, and the diodes shunt voltages a
little above your power supply to your power supply (which, hopefully,
will handle it and still regulate properly).  This is essentially what
the pic does, look in the data sheets for the schematics of the ports on
the pic.  Many a hobbyist has sat in wonder at seeing their pic last
through some stupid connection mistake....

-Adam

Micro Eng wrote:

> looking for a way to protect an I2C mux.  We have two RJ45 connectors,
> one
> with serial, one with I2C.  If they plug them in wrong, then it could
> (and
> probably did) blow the mux.  So is there a way to protect this? Next
> design
> will fix it by not allowing 12V on one of the I2C pins but for now we
> can't
> change the connectors/wiring scheme.
>
>
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