> > Open collector RA4 spec is a lot higher, 14V vs Vdd + 0.3V
> 
> Only on the really old PICs. It's something like 7 volts on anything
> current or was-recently-current.

For most PICs I use (including 18F) it's 8.5V, which is > Vdd max.
In the vast majority of applications only 5V is used but I have seen
RA4 used as a high-voltage pin (sensing and logic conversion for
example). That specs have been reduced could cause problems
with legacy products which can cope with 14V. But, as always,
check the datasheet. Things change and what might be a functional
drop-in might not be so wrt electrical specs

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