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MSP430F247 LFXT1

Bryan Busacco
Expert 1215 points

Other Parts Discussed in Thread: MSP430F247

 

I sampled a 38.4 KHz crystal from Microcrystal.   This is TI’s recommended vendor for the MSP430 microcontrollers.   I have the 38.4KHz crystal running on the LFXT1 pins on the MSP430F247.   I configured the SMCLK output pin to output the SMCLK, and it appears to be working fine.   My hesitation is, the TI datasheet seems to indicate that the 38.4KHz crystal is not an option.  

 In my case it provides a really nice (integer divisible) reference for the UART over temperature.  I do have a workaround if this is not a good idea.  I can always switch to the 32768 crystal, and run the DCO calibration periodically.  

 

Are you aware of any other people trying this?   Do you have any ideas on the pro’s and cons of doing this?

 Thanks,

Bryan Busacco

 

  • 0
    TI__Genius 16215 points

    Bryan,

    The XT1 crystal circuit is designed to operate at higher than the typical specification of 32.768kHz.  I have done bench test before with a 90kHz crystal and works. At the end of the day, it is also dependent on your load capacitance. If you have that right, the crystal should start-up. You should also take into account the start-up time of the crystal.

    Regards,

    William

  • 0
    Guru 227245 points

    The fLFXT1,LF parameter specifies 32768Hz as typical, it does not note any min/max value.
    It sounds reasonable that the oscillator supports other frequencies too, as long as the resulting oscillation duty cycle is within the limits, the fault detection isn't triggered and the driving capacity of the oscillator driver isn't exceeded.

    I'm a bit surprised that 90kHz are no problem when the datasheet lists 50kHz as maximum frequency for a digital input signal.
    But experiments on the G2 series (which do not have HF crystal support) revealed that the digital input takes even 16MHz.
    So the '50kHz max' entry has been proven much too low :)

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