The 16F87x chips (and others IIRC) include a separate low-power oscillator designed to run off a cheap 32Khz or similar low-speed XTAL. This osc then clocks timer 1, which can be used as a divider so that it only interrupts and wakes up the PIC every so often. Bob Ammerman RAm Systems ----- Original Message ----- From: "Pic Dude" To: Sent: Thursday, June 13, 2002 11:11 AM 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... > > 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. > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.