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How to Use the Kinetis RTC Time Compensation Register (RTC_TCR)?

Question asked by Alessandro Vagniluca on Dec 1, 2017
Latest reply on Dec 7, 2017 by Robin_Shen

I read the AN4949 application note http://cache.freescale.com/files/microcontrollers/doc/app_note/AN4949.pdf

but it refers to Kinetis-M devices and I still don't understand how to set RTC_TCR register for frequency compensation in a Kinetis-K device like.

 

The CIR field set the compensation interval in seconds (from 1 to 256 s): every compensation interval the prescaler value is adjusted for one cycle with the value of the TCR field (+128 / -127) from the 32768 nominal value, right?

 

Now, I can measure the RTC_CLKOUT signal frequency, which quite always differs from the 32768 Hz nominal value; but how to calculate the right values for CIR and TCR fields?

 

If I measure RTC_CLKOUT = 32767.0000 Hz, should I set CIR = 0 and TCR = 1 ?

But what if I measure RTC_CLKOUT with a fractional part, i.e. 32767.1234 or 32768.8765 Hz ?

 

Regards

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