whether this FRDM-K22F is using external or internal oscillator? how actually its configured in code ?
there are many different places where you can customize whether to use an internal reference clock or an external oscillator. I can't tell you which without knowing what project you are referring to. You will need to look through how your MCG, SIM, OSC, and/or RTC OSC registers are configured to determine whether internal or external sources are being used and how they are being used.
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