Hi Kev,

Speaking as a SX chips user, I'm not sure can pic12c508/9 does that:

1. set the pin as output with no pullup, and set it low
2. change the pin to input, and read it

The time it takes to charge the line high again will indicate the
level of your supply voltage.  Check the spec. of your chip to see if
diode is needed for protection.  And you might need extra capacitance
if the chip is not fast enough to detect the rise time of the inherent
capacitance.

Ling SM
sm.ling@cmpmail.com
http://www.i-pal.com (ready in a week time)

>I need to detect an "analogue" low signal (low battery warning!) on
gpio,3
with weak pullup enabled and wake up enabled, I could use an external
schmitt trigger but that would defeat the object of the pic!
I have tried a pot as a potential divider but the pic doesnt seem to
like
the slow rate of change? Schmitt trigger in programming mode only?
should I call a delay when checking  gpio,3?