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Question: How to check the waveform of the LSE - External 32.768KHz XTAL clock

Question asked by F Nabe on Sep 14, 2017
Latest reply on Sep 16, 2017 by F Nabe

I'm developing the firmware for our custom CPU-Board with STM32F769NIH6,
and checking RTC function using LSE clock.
It seems working correctly, but can't see the waveform of LSE clock.
Our circuit of the LSE clock is the same as "STM32F769 Discovery kit"(STM32F769I-DISCO) .
... External 32.768KHz XTAL connected to the MCU pins (PC14-OSC32IN, PC15-OSC32OUT) via resistor (0 ohm), and added the load capacitors.

 

I made a program by using CubeMX.
When the program is running, MCU register "RCC_BDCR" is set "0x8103".
I think that it mean...
  a. The LSE clock is used for RTC.
  b. The MCU is working well.
and RTC HAL fuction(SetTimeInfToRtc etc.) seems working correctly.

 

So, I checked PC15-OSC32OUT pin by using an oscilloscope.
But...
  a. I expected the LSE clock (32.768KHz). But,There is no LSE clock.
  b. There is just only several hundred mV flat line.
Of course, the PC14-OSC32IN pin also has no LSE clock.

 


I think that the waveform of the LSE clock can see at the MCU pins:
OSC32IN and/or OSC32OUT, is it correct?

 

Or another method/pin to check the LSE clock ?

 

# I need to see the waveform of the LSE clock because of adjusting
the value of the load capacitors for New 32.768KHz XTAL.

 


Please give me an information.
Thank you.

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