Of course it's not the IO input circiut leaking - it's the pair of static
protection diodes. One conducts from 0V to IO pin, the other from IO pin to
Vcc. These diodes can be used for other things like putting mains directly
into a PIC simply by current limiting. You can tie 240VAC (UK) into a pic
that's battery powered. Tie Neutral to 0V and LIVE to IO pin  via a 10M
resistor. This can be used to synchronise the PIC with the phase of the AC
and to derive an accurate 50Hz time base (very accurate over a period, less
so over short times). The 10M resistor limits the current and the static
prtection diodes leak the small current through to the battery. First time
you rig it up take a deep breath before switching on!

| -----Original Message-----
| From: JP.BROWN [mailto:J.P.Brown@BRADFORD.AC.UK]
| Sent: 08 June 2000 08:48
| To: PICLIST@MITVMA.MIT.EDU
| Subject: Re: [PIC]: Operation of PICs from low voltage

| on further inspection of the circuit I found that the 16F84
| was leaching a
| supply from the I/O pins (the external circuit was
| independently supplied)