Thanks, not sure I follow your calc's, I need to dig out some old notes on
ppm stuff and recheck them, but i will certainly give it more thought. I
will no doubt end up using a RTC to flywheel a signal from something like
a GPS reciever.

Mat


>> Last time I checked RTC's weren't accurate to micro seconds,
>> unless anyone knows of any which are?
>
> Maxim DS3231, +/- 2ppm, 0C - 40C (1 minute per 11.57 days)
>
> http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4627
>
> Taking 50us variation as 1ppm gain/loss and maximum drift,
> the time would be out by 100us after
>
> 1,000,000 * 50us * 2 = 100s
>
> A minutely refresh would guarantee synchronisation
>
>
>
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