[time-nuts] Switching oscillators
davidwhess at gmail.com
Mon Dec 10 00:11:01 UTC 2012
On Sun, 09 Dec 2012 15:49:04 -0800, Hal Murray
<hmurray at megapathdsl.net> wrote:
>lists at 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
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.
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