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RTC reference clock detection

Question asked by ada_fan on Oct 15, 2013
Latest reply on Oct 15, 2013 by Clive One

we want to build a system with some STM32F407s. For error memory, it is important that all controllers have the same time. I would like to use the RTC and the RTC_REFIN input to synchronize the RTCs.The RTC with LSE (32768Hz) runs fine. Only the synchronization does not work.On pin PB15 is a 50Hz signal. The pin PB15 is configured as an input pin. REFCKON in RTC_CR is also set. (PREDIV_A=0x7F and PREDIV_S=0xFF, RTC_CALIBR=0x00.)

I checked this issue with Calibration Clock Out (1s) and a wake-up interrupt (toggle a pin in Interrupt Service Routine)

(A timer I could easily sync with my exteren clock).

Does anyone have an idea where my mistake is?

Thanks you.