clarification of SLEEP command?

[picster]

<edit> - found this answered more or less elsewhere - no precision, it's WDT based.

In the manual, it states that the SLEEP Period command puts the uC in low power mode for Period seconds, BUT it wakes up "periodically" using the WDT and the internal RC clock, to CHECK and see if time is up.

My question is, does it use the WDT for counting ticks while "sleeping", or does it use its defined OSC for doing that part while sitting there doing nothing else? I understand the concept of it waking up now and then to check, but... is the periodic waking up cycle actually doing the counting itself, or is the uC doing the counting with the high precision OSC while in "sleep" mode?

I have used NAP, but it seems to be quite a different animal, from the descriptions. I want something that puts the chip into low power for a certain period of time (i.e. - 12 hours) with precision (within 2 seconds is fine).

TIA

picster