> Hmm... The PIC12F629/67 data sheet says typical current consumption of
> the WDT is about 300nA at 2V (See section 12.3, pg 88 of DS41190C). The
> total device current without anything enabled is typically 1nA. max
> 700nA, again at 2V.

This can vary between PICs, and the WDT current increases drastically with
voltage.  The incremental WDT current of a 16F630 at 3V is 2.7uA, and at
5V is 16uA.

> As I said before, I measured a current consumption ...

What you measured doesn't mean anything as long as it is at or below the
maximum guaranteed by Microchip.  Unless you're going to tell your
customer "The battery should last a year, but might only last one week.
If you happen to get some 1 week units, too bad", you need to stick to the
worst case specs.

> The only real
> problem is that the WDT period is dependent on temperature, so you
> can't get an accurate timeout.

Our micropower external wakeup oscillator period also varied greatly with
temperature, voltage, phase of the moon, proximity to a dead fish, etc.
We got around this by occasionally leaving the internal oscillator on for
a whole wakeup period to measure it.  The external oscillator could then
be used to track time to the accuracy of the internal R/C oscillator,
which is a couple percent if I remember right.  We did this measurement
every 1000 external cycles, so it only added a small amount to the average
power draw.  You don't need to do it very often because the supply
voltage, temperature, the moon, and dead fish just don't move that fast.

> However, if you are just polling for an
> event, that isn't really a problem. You can get a 20mS poll out of the
> thing pretty easily.

If you're polling for an event, the wakeup on change pins or the interrupt
pin can be very useful.


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