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...

Cheers,
-Neil.



-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Alan B. Pearce
Sent: Thursday, June 13, 2002 3:30 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: FCC question


>BTW, I wanted to use a 1Mhz on the petfeeder, but the
>odd thing is that digikey lists these for $7+ ea, while
>131.072khz, and 4MHz crystals are approx $2 ea.

I believe there is manufacturing hassles at around the 1MHz area. I am not
really sure what they are, but I suspect that it is a point where you cross
between two different modes of operation of the crystal physical vibration.
I remember when the HF Marine bands went to SSB the company I worked for
designed a receiver using a 1.4MHz filter, and had a horrible job getting
crystal filters for it, because the crystals were right in a difficult to
process frequency range.

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