[time-nuts] Holdover, RTC for Pi as NTP GPS source

Jim Harman j99harman at gmail.com
Wed Nov 1 20:16:17 EDT 2017

On Wed, Nov 1, 2017 at 7:21 PM, MLewis <mlewis000 at rogers.com> wrote:

> And the DS3231 has:
> - a 32K output, and
> - an Active-Low-Interrupt/SQW output that can be set to PPS.
> It's unclear to me how to sync the DS3231 PPS to the GPS PPS, or if that
> can be done.
The DS3231 has an 8 bit register that will change its frequency in
increments of about 0.1ppm. Thus you could discipline it to get its pps
aligned with your reference.

With an adjustment range of +/- 127, that's a maximum offset of 12.7 ppm.
In the worst case you would have to move its pps 0.5 sec, which by my
calculation would take about 41.667 seconds or about 11.5 hours.


--Jim Harman

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