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kohei ishikawa
kohei ishikawa
Visitor II
April 2, 2018
Question

STM32F030C6 trying to use LSE

  • April 2, 2018
  • 3 replies
  • 772 views
Posted on April 02, 2018 at 11:26

Hi, I have a STM32F0C6 board and I'm trying to use RTC function with LSE.

It seems RTC is working correctly and I can check the waveform of LSE Clock from MCO pin.

But when I check the waveform of OSC32_IN and OSC32_Out pins by using an OscilloScope,

OSC32_IN: about 300mV flat line

OSC32_Out: about 1.3V waveform nearly LSE clock(32.768KHz).

Is this correct work of OSC32_IN and OSC32_Out?

please give me an information.

and let me apologize for my poor English.

thank you.
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    3 replies

    waclawek.jan
    waclawek.jan
    Super User
    April 2, 2018
    Posted on April 02, 2018 at 15:24

    The LSE oscillator is a very low power (thus high impedance) analog circuit, thus it is very easy to be influenced by the attached oscilloscope probe (which presents a significant load).

    JW

    henry.dick
    henry.dick
    Associate II
    April 2, 2018
    Posted on April 02, 2018 at 15:37

    sounds about right. probing the output pin is better, as its impedance is lower.

    T J
    T J
    Senior III
    April 2, 2018
    Posted on April 02, 2018 at 16:27

    you can use a 1Meg resistor in series with your probe,

    then the oscillator should keep working whilst you are watching it.

    but you will shift the frequency with the probe capacitance.

    henry.****

    ‌ is correct, you should be probing the output pin.

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