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MSP430FR5962: Time measurement during the low power mode

Krams
Intellectual 560 points
Part Number: MSP430FR5962
Other Parts Discussed in Thread: MSP430FR5964

Hello, I am currently using a Msp430FR5962 controller. I put this in LPM3 mode (see code):

    // Clock System Setup
     CSCTL0_H = CSKEY_H; // Unlock CS registers
     CSCTL1 = DCOFSEL_0; // Set DCO to 1 MHz
     CSCTL2 = SELM__DCOCLK | SELS__DCOCLK | SELA__VLOCLK;
     CSCTL3 = DIVA__1 | DIVS__1 | DIVM__1; // Set all dividers to 1
     CSCTL4 = LFXTOFF | HFXTOFF;
     CSCTL0_H = 0; // Lock CS registers

     __bis_SR_register (LPM3_bits | GIE);

I would like to switch the MSP to low power mode and count (measure) the time until the MSP leaves the low power mode. The VLOCLK runs with the above code, but it is very imprecise and not temperature-stable.
What options do I have to put the MSP into a very low power mode and still measure a time with an approximate accuracy of + -1ms. Also over the temperature range from -40 ... + 85 ° C.

Furthermore, this clock generator must also start to oscillate relatively quickly, in a maximum of 5 to 10 ms.

What are my options?

  • 0
    TI__Expert 7365 points

    Hi Krams,

    Is using the LFXT an option?

    Srinivas

  • 0 in reply to Srinivas Lingam
    Intellectual 560 points

    I have to set the MSP430FR5964 to LPM3 mode and a clock source has supplied the ACLK.
    According to the data sheet, the clock source may have a maximum clock of 50 kHz.

    Therefore a 32kHz crystal would be a good solution, but unfortunately I need a clock source that is ready for use within 20ms.

    What other options are there for a clock source that is ready for use within 20ms and consumes very little power.

    Does Texas have any products that meet this requirement?

    E.g. astable multivibrator or RC oscillator or others?

  • 0 in reply to Krams
    Guru 88700 points

    I think the idea is that the crystal (LFXT) runs all the time, so startup time really only matters at power-up.

  • 0 in reply to Bruce McKenney47378
    Intellectual 560 points

    This is how you see it.

    I need a clock source that is ready and ticking within 20ms.

    After a maximum of 10s, Vcc is again 0 and the process starts again.

    Whatever. I need some kind of clock source that is ready within 20ms.

    Are there any Low Power RC oscillators or other ICs from Texas?

  • 0 in reply to Krams
    Guru 88700 points

    The external clocks I'm familiar with can give you the 100ppm you're looking for, but are rather high power and -- since they're based on crystals -- still take a long time to start up.

    The DCO and VLO both start up very fast. Have you considered calibrating the VLO using the DCO? Appnote SLAA340 suggests reasonable results in 3 ticks of the VLO, which is sub-millisecond. The accuracy won't be better than the DCO (more like 35000ppm than 100ppm), but temperature effects over 10 seconds should be small.

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