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Using external crystal

MSP430User
Prodigy 100 points
Other Parts Discussed in Thread: MSP430FR5969

Using MSP430FR5969 Launchpad, TI-RTOS 2.12 and CCS 6.1.

I would rather use an external 32.7kHz crystal oscillator for timing instead of the internal crystal for better accuracy, but when I probe the 2 pins of the external crystal, there is no signal on the scope, just noise. Am I probing incorrectly, or do you need to set register(s) to enable the external crystal?

I tried the below code (to set the pin multiplex mode to crystal instead of GPIO) but it just threw the board into a bootloop:

PJSEL1 &= ~BIT4;
PJSEL0 |= BIT4;
CSCTL4 &= ~LFXTBYPASS;

Is there anything you need to do in the config to set the RTOS timers module, etc to use the external crystal?

  • 0
    Guru 46710 points

    >Am I probing incorrectly
    Probably. You need FET probe. You can try 10x low capacitance probe on XOUT pin but it is still possible that your probe will upset oscillator - it is very sensitive and don't like external capacitances.

    It is advised to search forum for similar quations. One thread that is possibly helpful for you: e2e.ti.com/.../235484

    Have you looked at the code examples available on the device product folder in the Software section?

  • 0 in reply to Ilmars
    Prodigy 100 points
    But when I short out the pins of the crystal, it doesn't affect the timing at all. This leads me to conclude the board is using an internal crystal.
  • 0 in reply to MSP430User
    Guru 74080 points

    Normally you can output the internal clocks to some pins of the micro - there you have a buffered clock source where you can attach your probe. By the way: In your first post, you set a special function for BIT4, but where is the other pin of the crystal? If you do not use the bypass mode, then the crystal needs an input and an output.

  • 0 in reply to Dennis Eichmann
    Prodigy 100 points
    I want the board to use an external crystal for accuracy reasons, but it would be nice not to have to set registers. Is there a way to tell the RTOS to use the external crystal for the timer module? What about for the uart driver?

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