56F8367 CW8.0 ADC Calibration does not work

[forkstapler]

Hi,

I'm trying to use the calibration code that is given in the peripheral user manual on page 71-74.

First I don't know how I'm supposed to insert the data sheet values into the code (CF1= 0,002289 and CF2 = -25.6).

And if I test the calibration without using both correction factors I get a totally wrong value. Is there some code available that actually works?

Thank you

[rceit]

This is the respònse of technical support about our question:

Yes, you are right there is a mistake on the manual, unfortunately.

The error is in evaluating parameter cal_b_0 in line

cal_b_0 = Ya - (UInt16) (( (UInt32) cal_m_0 * (UInt32) Xa_ADC0 ) >> 15

);

This equation uses parameter cal_m_0, which is corrected by

CF1_CORRECTION parameter.

So the cal_m_0 and cal_b_0 have to be calculated without correction

parameters and these use in a final value calculating as

Y = (cal_m_0 + CF1_CORRETION)*X + (cal_b_0 + CF2_CORRETION).

Please refer to my code example below:

#define Ya (1023 << 3) // =  8184

#define Yb (3071 << 3) // = 24568

#define DATA_SHEET_PARAMETER_CF1        0.010380

#define DATA_SHEET_PARAMETER_CF2        -31.7

//For "m" correction, need fractional representation of data sheet value

/ 2

#define CF1_CORRECTION (FRAC16(DATA_SHEET_PARAMETER_CF1) * 16384 / 32768 )

// For "b" correction, shift data sheet parameter by 3 bits to allign

with RESULT reg.

#define CF2_CORRECTION ( (INT) ( DATA_SHEET_PARAMETER_CF2 * 8 ) )

static void CalibrateADC_m_and_b(void)

{

        Int16 Xa_ADC0, Xb_ADC0, Xa_ADC1, Xb_ADC1;

        Xa_ADC0 = low_ADC_cal_0; // =  8304

        Xb_ADC0 = high_ADC_cal_0;// = 24600  values measured

        Xa_ADC1 = low_ADC_cal_1; // =  8312

        Xb_ADC1 = high_ADC_cal_1;// = 24576

        cal_m_0 = (UInt16) div_s( ( Yb - Ya) >> 1, ( Xb_ADC0 - Xa_ADC0 ); // = m/2 = 16472

        cal_b_0 = Ya - (UInt16) (( (UInt32) cal_m_0 * (UInt32) Xa_ADC0 )

>> 14 );

// =Ya - m*Xa  = (1023*8) - [(m/2 + CF1/2)*8304]/16384 = 8184 -  

[(16472*8304)/16384] = 8184 - 8348 = -164 //

}

static void CalibrateADCvalue( void )

{

       UInt16 ADC_Val_1, ADC_Val_2;

       ADC_Val = getReg( ADCA_ADRSLT0 ); // = 9448  value measured

       if ( cal_b_0 ) // Have we done calibration yet?

      {

            // First, multiply by m/2, and shift the result to give the

correct

            // bus position.

    ADC_Val_1 = (UInt16) ( ((UInt32) (cal_m_0 + CF1_CORRECTION) *

(UInt32) ADC_Val )  >> 14 );

      // = [(m/2 +CF1/2)* X]/16384 = (16472+170) * 9448/16384 = 9597

        // Then, add the expected offset.

        ADC_Val_2 = ( ADC_Val_1 + cal_b_0 + CF2_CORRECTION ) ; //

(9597-164-254) = 9178

        ADC_Val = (word) ADC_Val_2;

        }

}

This is the way how to obtain the right calibrated value

[rceit]

Correction:

#define CF1_CORRECTION ((DATA_SHEET_PARAMETER_CF1 / 2) * 32768 )

or

 #define CF1_CORRECTION (FRAC16(DATA_SHEET_PARAMETER_CF1 / 2))

both definitions are correct.

[rceit]

Hi, I am trying to calibrate the ADC's too and I think there could be some mistakes in the Peripheral User Manual.
In the figure 2.13 (page 73) I think it must appear:
cal_b_0 = Ya - (UInt16) (( (UInt32) cal_m_0 * (UInt32) Xa_ADC0 ) >> 14 );
instead of:
cal_b_0 = Ya - (UInt16) (( (UInt32) cal_m_0 * (UInt32) Xa_ADC0 ) >> 15 );
and:
cal_b_1 = Ya - (UInt16) (( (UInt32) cal_m_1 * (UInt32) Xa_ADC1 ) >> 14 );
instead of:
cal_b_1 = Ya - (UInt16) (( (UInt32) cal_m_1 * (UInt32) Xa_ADC1 ) >> 15 );

That is because the maximum value for cal_m_0 and cal_m_1 is 2^15, but they represent m/2 in both cases.

Then, in figure 2.14 (pag 74), it must appear:
ADC_Val_2 = ADC_Val_1 + cal_b_0;
instead of:
ADC_Val_2 = ( ADC_Val_1 + cal_b_0 ) << 1;

Is this correct??

I have another question:
I suppose we must consider CF1_CORRECTION as FRAC16(0.002289/2):
#define CF1_CORRECTION FRAC16(0.002289/2)
but how we must consider CF2_CORRECTION?? Is the following sentence correct??
#define CF2_CORRECTION ((Int16)(-25.6 * 8))
Thank you very much in advance.

[trytohelp]

Hi,

Your request requires some investigation.

Can I propose you to log this issue directly in the Technical support system ?
Please use Freescale on line support web page.
  - Go to following URL: http://www.freescale.com/TechSupport
  - Click on Submit a Service Request. You will come to a login page.
  - You can submit your request through the web from there.

Please provide us more details about the Tool version used.
To do that you must:
* CW:
Start the IDE and click on Help | About Metrowerks CodeWarrior.
Click on Installed Products 
Provide us all info displayed.
Or you can save them in a txt file.

Pascal

[trytohelp]

Hi,

Sorry for the delay.

Can I propose you to log this issue directly in the Technical support system.
Please use Freescale on line support web page.
  - Go to following URL: http://www.freescale.com/TechSupport
  - Click on Submit a Service Request. You will come to a login page.
  - You can submit your request through the web from there.

Please provide us more details about the Tool version used.
To do that you must:
* CW:
Start the IDE and click on Help | About Metrowerks CodeWarrior.
Click on Installed Products 
Provide us all info displayed.
Or you can save them in a txt file.

Pascal