> -----Original Message-----
> From: Pic Dude [SMTP:picdude@AVN-TECH.COM]
> Sent: Thursday, June 13, 2002 4:12 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [PIC]: FCC question
>
> In my sleep last night I was trying to devise a system
> running 2 clocks -- the pic would run in a basic RC
> system setup for about 1 MHz, and that would handle all
> the display and other perihperal stuff; and I'd use an
> external oscillator at any low frequency (32.788 or less
> if available) to generate the 1hz signals for the clock.
> This would have to be sent to the external interrupt
> pin.
>
> However, AFAIK (w/o looking at docs), I can't assign a
> pre-scaler to that interrupt, so it seems like I'd get
> way more interrupts than I need and it seems wasteful,
> and may cause some confusion during EEPROM writes, etc.
>
> Yes, I'm avoiding using external freq dividers.  Need to
> think and research some more about this one...
>
Don't know which PIC you are using but the bigger ones with timer 1 have
provision for a second crystal to drive  timer 1.  If not you could use an
external oscillator and drive TMR0 and intterupt on overflow .  32.768Khz
needs to be divided by 2^15 to get 1 second, so setting TMR0 pre-sclaer to
1:128 and interrupting on rollover (1:256) would give exactly 1 second
interrupts.

Regards

Mike

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