Hi Team,
I need some help to understand what I am doing is correct or wrong. A required guide from ST's expert
Basically working on RTC temperature Drift compensation, so I have referred the RTC temperature compensation APP document from ST's
The link provides: https://www.st.com/resource/en/application_note/an2604-stm32f101xx-and-stm32f103xx-rtc-calibration-stmicroelectronics.pdf
I am using STM8AL3189 MCU,
For RTC calibration, we have CALP = 1 *512Clock Pulse
CALM = [8:0] ==> 0 to 0x1FF
using combination of CALP and CALM we can achieve up to 511 to 512 Clock pulses
Question 1 :
Steps followed to calibrate the RTC temperature compensation
- RTC clock is 32768Hz, K = -0.04ppm/*c^2, To = 25*c, T = calculating from the internal junction temperature
- acc = 20 + k *(T – To)^2;
- After calculating the acc, I have come up with this formula provided from ST's to Convert this PPM to clock
Here, I have attached the excel sheet to calculate both the negative and positive PPM value
question 2: I have enabled calibration out for RTC 512Hz, and if I probe that to logic analyzer
I am seeing 
512.033
512.031
512.035
512.033
Average = 512.0334
(512/512.0334) - 1 *1000000 ==> -65.23ppm (but is this correct) since i referred from APP notes
Question 3:
How frequently need to update the CALP and CALM values to compensate for the drift and how to validate and when need to measure after the calibration using a 32second window (-487.1 to 488.5 ppm) with a resolution of 0.954ppm?
can you please guide the process is which following is correct or wrong for all the questions?
Thanks in advance.
Regards,
Anand Kumar N S
