Hi Some chips (dspic33's for example) have "oscillator fail" protection. You blow the magic fuse bits and when the TBolt isn't giving you a clock the micro drops back to the internal R/C oscillator. It's magic....
Bob -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Chris Albertson Sent: Wednesday, September 12, 2012 11:38 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts]Automatic switching of a µC osc. to external 10MHz reference as clock? On Tue, Sep 11, 2012 at 6:31 PM, Kevin Rosenberg <ke...@rosenberg.net>wrote: > On Sep 11, 2012, at 4:42 PM, Peter Krengel <krengelda...@gmx.de> wrote: > > I'm looking for a possibility to make an automatic switching > > between the internal µC oscillator (Atmel µC) to the 10MHz output > > of my thunderbolt to use it as a precise µC clock. Has anybody an idea > how to do best > > without disturbing the accuracy of the ref. signal? > > Hi Peter, > > I'm likely misinterpreting what you want to do. From my reading your > question, the answer is: no, you can't the change the source of an AVR's > system clock bus at runtime. You can only change the CLKSEL fuses only > during programming. > I don't think he was talking about fuses. The way I'd do this is to have a "quality" 10MHz oscillator supply the uC clock pin. This 10MHz oscillator is phased locked with a reasonably long time constant to either a local 10MHz TTL can oscillator or to a BNC jack. When the jack is connected to the t-bolt the local oscillator will lock to it otherwise it falls back to the TTL can. The long TC on the PPL is so there to prevent a transient when the switch is flipped. I assume one would use a toggle switch but it could be automated by detecting power through a narrow bandpass filter from the BNC jack. Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.