I am about to order a proto board for a product but my customer wants =20
a digital clock feature added at the last minute (surprise!).  It's =20
setup for a 16F883, but I'll be migrating the code to a 18F24K22 soon. =20
  The clock will have to be setup for low-power sleep operation, =20
waking periodically keep accurate time.

Problem: T1OSI/T1OSO is already used (all of PortC drives display =20
segments), and shuffling what's already on those pins to other =20
ports/pins creates other confusion.

PIC is currently running on the internal OSC at 8Mhz, and RA7/CLKIN is =20
available, but external/monolithic 32.768khz oscillators are pricey.

What I'm not clear on, is that if I run the PIC from an external =20
oscillator (say 12Mhz, 20ppm crystal) instead, can I use that =20
instruction clock to wake the PIC periodically?  The Timer1 diagram =20
(figure 6-1 on the 16F883 datasheet) suggests I can drive Timer1 from =20
the instruction clock/4, and get the same interrupts, but I'm not =20
clear on the process of running the PIC simultaneously from this =20
clock.  I don't think it should matter, but I feel like I'm missing =20
something.

Or is there some simpler method to do this?

Cheers,
-Neil.


--=20
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