I did something like this with a 16F870. There's a 32 kHz crystal on the timer 1 oscillator on the chip. Something like every 1.6 seconds (if I recall correctly), the timer overflows and wakes the chip up. It then runs at 4 MHz, does stuff, then goes back to sleep. Also, the 18C452 (and similar) has a clock switch so you can switch the processor core between two speeds. I haven't used it, but it's interesting... Harold On Thu, 13 Jun 2002 10:11:52 -0500 Pic Dude writes: > 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. > > FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com Reach broadcasters, engineers, manufacturers, compliance labs, and attorneys. Advertise at http://www.hallikainen.com/FccRules/ . ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: http://dl.www.juno.com/get/web/. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.