George wrote:

>On Tue, 23 Jun 1998, Craig Lee wrote:
>
>> If you be meaning the missing pullup on RA4 on the 16F84 for instance,
this
>> is
>> because you may wish to control a device that may have a 12V swing to
it.
>> If a pull-up
>> to the 5V supply was there, you would have an unwanted configuration
>> wouldn't
>> you.
>>
>
>I think the 16F84 specs say that voltage on any pin including RA4 must
not
>exceed supply voltage by more than 0.something volts. Due to the
internal
>clamping diodes, you would have a hard time coming over supply+0.6V
>anyway.
>
>Being able to switch high voltages with RA4 would be a nice feature,
>though. Maybe we could talk Microchip into YAR (yet another revision)...
>;-)
>
>Georg.

The data sheet does say that the voltage on any pin should be -0.6v to
VDD+0.6v (and I guess it's because of the protection diodes, as you quite
rightly say) BUT it also says that the open drain pin (RA4) only has
protection diodes connected to VSS only!  Well, if this is true, I would
think that the voltage on the open drain could go higher.

Has anyone used this pin to control voltages above VDD ?

Brian