> The datasheets is DS30081F page 21: (quote) 'Note: I/O pin has protection
 diodes
>  to Vss only.'
> I just tried measuring a device, and the datasheet is ofcource correct. Only a
>  diode to Gnd (Vss) can measured.
> One of the advantages of an O/C (or Open Drain) output is that you can switch
>  between Gnd and a voltage higher than Vcc.

The data sheet says the pin does not have the diode, but it says nothing
about the maximum allowable voltage on the pin other than the "any pin"
spec.  For any other "any" pin, the requirement that the pin not exceed
VDD makes sense because of the parasitic diode; for the RA4 pin, however,
the documentation does not say you can exceed VDD without damaging the
device--merely that there's no diode to prevent you from doing so.

I'd be thrilled if I had some confirmation that the pin could be used to
switch 9 or 12 volts; I've not seen such a thing documented, however, and
would not wish to use it in a design without assurance that it was safe
to do so.  Does anyone at Microchip know the scoop?