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Last updated: 27 Aug 2020
The Freedom-K64F is an ultra-low-cost development platform for Kinetis K64, K63, and K24 MCUs.

K64F RTC crystal frequency tests

Topic last updated 01 Oct 2018, by enrique iglesias. 2 replies
tom dunigan
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....

Anna Clements
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?

enrique iglesias
01 Oct 2018

Hi, I am using MK64FN1M0VLL12 processor and working on RTC. But in the first line itself getting a hard fault. I tried to solve it but failed. . External 32.768KHz crystal, Battery connected. And then I got the help from the https://goo.gl/e9rJuM and you will get the help.