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MSP430FR5739 RTC Calibration Problem

Murat Celebi
Prodigy 50 points
Other Parts Discussed in Thread: MSP430FR5739

Hi;

I am using MSP430FR5739 Experimenter's Board.   RTCCLK is configured to output at a frequency of 1 Hz . I measured   RTCCLK is 1.0000279 Hz.   This frequency error is approximately 27.9 ppm too high.  To decrease the frequency by 27.9 ppm, RTCCALS is cleared, and RTCCAL is set to  13 (27.9 /2.17). 

My code is :

RTCCTL23 |=  RTCCALF_3;             

RTCCTL23 |=   RTCCAL3 + RTCCAL2 + RTCCAL0;       

P1DIR  |= BIT0;        

P1SEL1 |= BIT0;  

I calibrated RTCCLK, measured RTCCLCK again.  RTCCLK result is 1.0000279 Hz. 

My questions is :

Can  I see effect of the calibration  in the period of 1 sec?   or  Can  I see effect of the calibration  in 1 hour? 

MSP430FR5739  user guide says;

"""Each RTCCALx calibration bit causes either 256 LF crystal clock cycles to be added every 60 minutes or 512 LF crystal clock cycles to be subtracted every 60 minutes, giving a frequency adjustment of approximately -2 ppm or +4 ppm, respectively. """

What exactly is described in the above sentence. How the calibrated signal is observe at the end of the calibration

Thanks and greetings,

Murat Çelebi

 

  • 0
    Guru 227245 points

    Murat Celebi said:
    Can  I see effect of the calibration  in the period of 1 sec?   or  Can  I see effect of the calibration  in 1 hour? 

    Murat Celebi said:
    ""Each RTCCALx calibration bit causes either 256 LF crystal clock cycles to be added every 60 minutes or 512 LF crystal clock cycles to be subtracted every 60 minutes,

    So each hour, there will be a shorter or longer second. Once.

    Internally, I guess (though I do not know), the hardware will add the calibration to the prescaler when the minutes roll over (for a shorter second) or something like this.

  • 0
    Prodigy 20 points
    Hi Murat!
    I'm trying to calibrate my FR59969, I managed to set P1_0 as RTCCLK.
    But what did you do exactly to calibrate it?

    Would I have to count how many times within an hour did it pulse?

    How did you measure your frequency? I'm using an osciloscope, but I wanted to periodically calibrate my FR5969.

    Thanks...

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