> If you put a 4.7V zener, anode to your I/O pin and cathode to Vdd,
> if will conduct when the I/O pin is below -4.7V respect to Vdd, i.e.
> when it's below ~0.2V with respect to Vss.

Ah, OK. Wasn't quite what I imagined (one of *those* days, but at
least you got me thinking)

So it will conduct at Vss + 0.3V (although a zener may have a
+/- 0.3V regulation range). If you have a true 0V signal coming in
then that could cause excess power consumption if the zener
conducts. A signal might need to be > 0.6V < threshold for a "0"

> It works.. I checked it.. but I wish I had an oscilloscope to check
> the transients as well

Typical for a Philips 4V7 is ~300pF max @ 1MHz.  A BAT46
is around 8pF @ 1MHz. I'm not sure if there's a spec stated for
the PIC's internal diodes

I think I still prefer the tighter specs of a Schottky

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu