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LP-MSPM0G3507: External LFCLK_IN reset & hang up

Loan Nguyen
Prodigy 25 points
Part Number: LP-MSPM0G3507

Hi,

I want to use the RTC with LFCLK_IN as the clock source for LFCLK, instead of the LFOSC as this internal oscillator has big tolerance.

So I removed the 32KHz Xtal on the board, and installed R11 with 50 Ohm resistor.

Here's the idea, the clock source for external LFCLK_IN is from one of the PWM pin.  Basically it is the 32MHz HFOSC divides down to 32.768KHz and output at pin PB15, then jumps back to pin PA4.

It's kind of running now and RTC calendar works fine, but whenever the RESET button S3 is pressed, the program hangs up.  The only thing can bring it back is to unplug the USB power and plug back in.

As I read somewhere, once the ext LFCLK is select the LFOSC can't be re-enabled unless we do a BOOTRST. 

But what is BOOTRST? Unplug power does same thing? Can we do it in SW?

Is this setup possible or it will hang up in the field and require a power recycle like that ?

Thanks   

  

  • 0
    TI__Prodigy 570 points

    Hi Loan,

    The BOOTRST stands for boot reset, one of the five reset levels, and you can find relevant explanation in BOOTRST chapter in MSP G-series Technical Reference Manual.  

    In fact, the RESET Button S3 triggers Power-on Reset (POR) in the same way as cold power-up (USB plug-in), so the issue described by you is not supposed to occur theoretically. 

    Here are two suggestions: 

    1. We recommend you use external active digital clock input instead of division from SYSOSC. 
    2. Conduct user calibration for LFOSC (up to ±240ppm total). And our SDK comprises corresponding example codes to accelerate self-serve process.

    Thank you.