btw: The PIC18Cxx2 chips support this directly, using an alternate clock on other pins. But of course 18Cxx2 are not exactly appropriate for cost-sensitive designs! Bob Ammerman RAm Systems (high performance, high function, low-level software0 ----- Original Message ----- From: D Lloyd To: Sent: Wednesday, June 28, 2000 10:40 AM Subject: Re: [PIC]: P 'Two speed' clock support > > > Hi, > > So it would seem that there is no 'on chip' support for such functionality.... > The application is cost sensitive so precludes the use of anything too > messy/complicated/costly externally. That's not to mention the hazards, as Bob > suggested, of dodgy edges. > Looks like another route is necessary. > > Thanks again, > > Dan > > > > > |-------------> > |(Embedded | > |image moved | > |to file: | > |pic10075.pcx)| > | | > |-------------> > >------------------------------------------------------------------------| > |"M. Adam Davis" | > |28/06/2000 13:13 | > >------------------------------------------------------------------------| > > > > Please respond to pic microcontroller discussion list > > To: PICLIST@MITVMA.MIT.EDU > cc: (bcc: Dan Lloyd/GBPTD/ABB) > Subject: Re: [PIC]: P 'Two speed' clock support > > Security Level:? Internal > > > > I believe I've seen oscillators with built in selectable dividers, but I cannot > remember where. You can use a seperate oscillator and divider, and use a pic > output or two to set the divider when necessary. > > -Adam > > D Lloyd wrote: > > > > Hi, > > > > I've been looking towards using a PIC for a 'dual speed' operation; running > the > > PIC from a (small) battery during a power failure (sleep then wake up, even at > > the lower oscillator rate......or maybe run all the time) then resuming full > > power operation when power is restored. As things go, the oscillator speed > for > > achieving the reduced power mode requirements does not provide enough > processing > > "oomph" when full power is available. Hence, dual-clock operation would be > > beneficial. > > > > I've had a poke around on the mchip site/checked out a few data sheets and I > > cannot really find too much information or a specific micro that performs > this. > > Mitsubishi etc make micros that specifically support this - is it blatantly > > obvious how to do this with the PIC and I have missed it, or is it just not > > possible? > > > > I've seen a posting where an RC oscillator is used where additional resistance > > is switched in and out via an I/O pin (dual speed) but I don't think RC is > going > > to give me the clock accuracy that is required. > > > > Any comments would be appreciated. > > > > Regards, > > > > Dan > > > > > >