topic Re: Hardware averaging of internal temperature sensor gives random values. in Kinetis Microcontrollers

Hardware averaging of internal temperature sensor gives random values.

larsl — Tue, 19 Nov 2013 14:48:34 GMT

Hi!

I'm currently running a set of prototypes on the MKL04Z32xxx4 MCU. I've written some code for the ADC in order to be able to read a set of different channels. All used channels are working fine when hardware averaging is turned on, except the internal chip temperature one. The code is set up to use 12-bit measurements, and looks does this after calibration:

	ADC0_SC1A \|= ADC_SC1_AIEN_MASK; //Enable interrupt
	ADC0_CFG1 \|= ADC_CFG1_MODE(1); // Set 12 bit mode


	//ADC0_SC3 &= (uint8_t)(~ADC_SC3_AVGE_MASK); //Averaging disabled when this line is run.
	ADC0_SC3 = ADC_SC3_AVGE_MASK \| ADC_SC3_AVGS(0); //4 samples enabled with this.

I can get a proper reading on the chip temp when hardware averaging is turned off (un-commented line above), but not when the code runs as above. I've recorded twenty samples over a period of 20 seconds. As you can see the one with HW averaging acts in a random fashion...

//4 HW samples:

array[0] uint16_t 1216

array[1] uint16_t 941

array[2] uint16_t 783

array[3] uint16_t 850

array[4] uint16_t 822

array[5] uint16_t 928

array[6] uint16_t 903

array[7] uint16_t 980

array[8] uint16_t 958

array[9] uint16_t 807

array[10] uint16_t 717

array[11] uint16_t 906

array[12] uint16_t 821

array[13] uint16_t 793

array[14] uint16_t 821

array[15] uint16_t 806

array[16] uint16_t 1102

array[17] uint16_t 822

array[18] uint16_t 906

array[19] uint16_t 643

//With averaging disabled:

array[0] uint16_t 1412

array[1] uint16_t 1412

array[2] uint16_t 1412

array[3] uint16_t 1412

array[4] uint16_t 1412

array[5] uint16_t 1412

array[6] uint16_t 1412

array[7] uint16_t 1412

array[8] uint16_t 1412

array[9] uint16_t 1412

array[10] uint16_t 1412

array[11] uint16_t 1412

array[12] uint16_t 1412

array[13] uint16_t 1412

array[14] uint16_t 1412

array[15] uint16_t 1412

array[16] uint16_t 1412

array[17] uint16_t 1412

array[18] uint16_t 1412

array[19] uint16_t 1412

Does anybody know what might be going on? This problem is driving me nuts..

Thanks!

/Lars

Re: Hardware averaging of internal temperature sensor gives random values.

Paul_Tian — Wed, 20 Nov 2013 03:00:55 GMT

Hi, Larsl

Would you please help to show your complete ADC initial code? I would like to check it for you. Thanks a lot. Have a nice day.

Best Regards

Paul

Re: Hardware averaging of internal temperature sensor gives random values.

larsl — Wed, 20 Nov 2013 07:22:01 GMT

Hi Paul,

Thanks for the fast reply. My calibration function looks like this:

static uint32_t adc_calibrate(void)

{

uint32_t ad_calib = 0;

irq_disableInt(irq_ADC); //Disable the interrupt while calibrating

ADC0_SC3 &= ~ADC_SC2_ADTRG_MASK; // Enable Software Conversion Trigger for Calibration Process

ADC0_SC3 &= (~ADC_SC3_ADCO_MASK & ~ADC_SC3_AVGS_MASK); // set single conversion, clear avgs bitfield for next writing

ADC0_SC3 |= (ADC_SC3_AVGE_MASK | ADC_SC3_AVGS(3)); // Turn averaging ON and set at max value ( 32 )

ADC0_SC3 |= ADC_SC3_CAL_MASK; // Start CAL

while ((ADC0_SC1A & ADC_SC1_COCO_MASK) != ADC_SC1_COCO_MASK)

; // Wait until calibration ends

if ((ADC_SC3_REG(ADC0_BASE_PTR) & ADC_SC3_CALF_MASK) == ADC_SC3_CALF_MASK)

{

return(FALSE); //Calibration failed.

}

ad_calib = ADC0_CLP0; // Add results

ad_calib += ADC0_CLP1; // Add results

ad_calib += ADC0_CLP2; // Add results

ad_calib += ADC0_CLP3; // Add results

ad_calib += ADC0_CLP4; // Add results

ad_calib += ADC0_CLPS; // Add results

ad_calib /= 2; // divide by 2

ad_calib |= 0x8000; // Set MSB

ADC0_PG = ad_calib;

ADC_SC3_REG(ADC0_BASE_PTR) &= ~ADC_SC3_CAL_MASK; /* Clear CAL bit */

return(TRUE); //Calibration successful

}

The remaining setup code calls this calibration function as below:

if(adc_calibrate()) //If we have a successful calibration

{

ADC0_SC1A |= ADC_SC1_AIEN_MASK; //Enable interrupt

ADC0_CFG1 |= ADC_CFG1_MODE(1); // Set 12 bit mode

ADC0_SC3 &= (uint8_t)(~ADC_SC3_AVGE_MASK); //Disable averaging

//ADC0_SC3 = ADC_SC3_AVGE_MASK | ADC_SC3_AVGS(0); //4 samples

}

After this the conversion is started with:

ADC0_SC1A = ( CHANNEL_TO_MEASURE & ADC_SC1_ADCH_MASK) | ADC_SC1_AIEN_MASK; //Start next conversion!

The result is extracted from the interrupt with

value = ADC0_RA;

I hope this was what you were looking for. In case it makes any difference, the MCU runs on 3.3V, and the analog reference voltage is 2.048V.

Thanks for the help!

Kind regards

Lars