Two pics is a fun idea, and I have worked through this same thought process
as well with much the same conclusions as Morgan and Dan.  Ultimately I
decided it was far easier and cheaper to use a more appropriate processor,
but I'd also like to throw out the other thing I came up with:

Epson's RTC-4574 will allow you to keep the PIC asleep almost all the time
(having it wake on pin change).  This change can be an event outside the
system, or one of the RTC's programmable intervals.  So you can use the
internal oscillator, have your accurate time base, and very low power.  And
the RTC periodic output could function as your watchdog as well, so you
could skip using the PIC internal WDT for even lower power.

Lastly, I don't think you can get the 15uA Dan mentions below when using the
WDT.

Bruce Cannon
Style Management Systems
http://siliconcrucible.com
(510) 787-6870
1228 Ceres ST Crockett CA 94525

Remember: electronics is changing your world...for good!


> I really really like the PICcyBackWartPoacher idea, with a tiny PIC
> like 12C6xx or an 18-pin'er, running at 32Khz, monitoring critical
> I/O and A/D lines, and bringing up the big guy when needed. At 32khz,
> you can get both continual [albeit slow] processing and very low
> power draw, 15uA. Having a local net for comm/updates is good, or
> storing/reading shared EPROM.
>
> best regards,
> - dan michaels
> ==============

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