The Freedom-K64F is an ultra-low-cost development platform for Kinetis K64, K63, and K24 MCUs.

K64F RTC crystal frequency tests

27 Oct 2015

I have measured the frequency of various MCU crystals and various RTC crystals using GPS PPS and NTP hosts, see https://github.com/manitou48/crystals/blob/master/crystals.txt

My K64F RTC crystal seems to be off by 250 ppm. The 32khz crystal is spec'd at 20ppm. I measured frequency error with GPS PPS, NTP, and the following program https://developer.mbed.org/users/manitou/code/k64f_rtcisr/

It could be that my RTC crystal is "bad", or maybe it's a systemic problem (wrong caps or PCB routing or ???). Maybe others could try measuring RTC ppm error on their K64F's and post results....

19 Apr 2017

Hi Tom, I have a number of k64Fs monitoring a variety of variables in some tests, and have found similar RTC issues. My crystals seem to be off around 300 ppm. Did you ever find out why this might be?

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