Hi Jacob,

> 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.

Woah boy.  Just remember that you are not talking about a ULN2003 relay
driver here.  The PIC16C/F84(A) could be inadvertently be put into
Probramming mode if you pull the _MCLR pin too high (especially
when Vcc is low)  If you must have a 6V open collector output
from say a set of batteries and you know that you chip will
reset correctly (open collector reset IC connected to _MCLR then
you can probably get away with it even if you put a low drop regulator
onto the rest of the IC and run it at 5V.

If you want open collector at above supply voltage then put in the
transistor and resistor and feel safe.

Cheers
--
Kalle Pihlajasaari     kalle@data.co.za
Interface Products     Box 15775, Doornfontein, 2028, South Africa
+27 (11) 402-7750      Fax: +27 (11) 402-7751