On Sun, 09 Dec 2012 15:49:04 -0800, Hal Murray <hmur...@megapathdsl.net> wrote:
>li...@rtty.us said: >> 1) Convert them both to logic levels and use a gate. >> 2) Use a relay. >> Both would need some sort of timer to drive them. Both would disrupt the >> instrument when the switch took place. I know of no "cheap / easy" ways to >> take care of the switching glitch. There are fancy / expensive ways. > >Switching clocks is really hard if they are driving digital logic that you >want to keep working correctly. You have to avoid runt pulses. Is that what >you mean by "switching glitch"? I linked this article last time someone asked about glitchless clock switching: http://www.eetimes.com/electronics-news/4138692/Techniques-to-make-clock-switching-glitch-free The Racal Dana 1992 automatically switches clocks when an external reference is applied but all of the details are hidden. I suspect its processor qualifies the external clock somehow before switching. I have done the something similar on microcontrollers where instead of glitchless external clock switching, I switched to the internal clock or auxiliary 32KHz oscillator, swapped the external clock, and then switched back to the external clock. _______________________________________________ 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.