On Wed, 9 Oct 1996, Jacob Blichfeldt wrote:

> 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.

Okay as far as it goes, but there IS an input buffer connected to that
pin as well.  You'd need to measure leakage current with 14V applied to
test this empirically, not just ohm it out.

> 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.

Can be, if the output is specified to permit it.  Does the F revision of
the datasheet spec that pin for higher voltage tham most of the rest?
The E version does not - all other [than Vdd or MCLR] pins are spec'd
only to 0.6V above Vdd.  Lacking an (input) protection diode is not
enough to permit reliable operation above Vdd -there were LOTS of OC TTL
gates that would fry if you went much over 5V, and those outputs really
were bare open collectors (aside from parasitic junctions).