RTC Calibration - AN2604 wrong?

[trond]

Posted on September 04, 2015 at 09:46

Hi!

AN2604 (http://www.st.com/web/en/resource/technical/document/application_note/CD00167326.pdf) states a formula for calculating PPM. The formula is as following: 

f32_Deviation=((f32_AvgFreq-511.968)/511.968)*1000000;

However, I wonder why is this 511.968? What we are comparing is the deviation from 32766 kHz divided by 64 which yields 511.969.

Is AN2604 wrong?

#rtc #stm32f1 #an2604