16.5.1 Gain Error Calibration

Gain Error Calibration Example

#include <xc.h>
int32_t result = 0; 			// ADC conversion result output.
int32_t coefficient; 			// Gain compensation coefficient.
void OscillatorInitialization(); 	// Oscillator initialization procedure.

int main() {
    OscillatorInitialization(); 	// Initialize the oscillator.
    // Enable ADC.
    AD1CONbits.ON = 1;
    // Wait when ADC will be ready/calibrated.
    while (AD1CONbits.ADRDY == 0);
    ////////////////////////////////////////////////////////////////////
    // GET A COEFFICIENT FOR THE GAIN ERROR COMPENSATION
    ////////////////////////////////////////////////////////////////////
    // Select oversampling mode.
    AD1CH0CON1bits.MODE = 3;
    // 256 conversions
    AD1CH0CON1bits.ACCNUM = 3;
    // Software trigger will start a conversion.
    AD1CH0CON1bits.TRG1SRC = 1;
    // Back-to-back conversions
    AD1CH0CON1bits.TRG2SRC = 2;
    // Select the AN6 input which is connected to 15/16 of AVDD
    AD1CH0CON1bits.PINSEL = 6;
    // Select signal sampling time (6.5 TADs = 81nS @ 80MHZ ADC clock).
    AD1CH0CON1bits.SAMC = 3;
    // Average 256 results of the reference voltage
    AD1SWTRGbits.CH0TRG = 1;
    // Wait when the result is ready
    while (AD1STATbits.CH0RDY == 0);
    // Oversampling result is 16 Bit (has additional 4 bits).
    // Calculate the gain compensation coefficient.
    // The coefficient is in fixed-point format (18 bits before point).
    coefficient = (long) (3840.0 * 16.0 * (1 << 18) / AD1CH0DATA);
    
    ////////////////////////////////////////////////////////////////////
    // CONVERT AND COMPENSATE THE GAIN ERROR
    ////////////////////////////////////////////////////////////////////
    // Clean channel register for new settings.
    AD1CH0CON1 = 0;
    // Select single conversion mode.
    AD1CH0CON1bits.MODE = 0;
    // Software trigger will start a conversion.
    AD1CH0CON1bits.TRG1SRC = 1;
    // Select the AN0 input for conversions
    AD1CH0CON1bits.PINSEL = 0;
    // Select signal sampling time = 0b11111 = 62.5Tad
    AD1CH0CON1bits.SAMC = 0b11111;

    while (1) {
        // Trigger channel # 0.
        AD1SWTRGbits.CH0TRG = 1;
        // Wait for a conversion ready flag.
        while (AD1STATbits.CH0RDY == 0);
        // Read result. It will clear the conversion ready flag.
        // The gain error correction coefficient is in fixed-point format
        // (18 bits before point).
        result = ((long long)coefficient * AD1CH0DATA) >> 18;
    }
    return 1;
}

void OscillatorInitialization(){
    PLL1CONbits.ON = 1;
    OSCCTRLbits.PLL1EN = 1;
    while(OSCCTRLbits.PLL1RDY == 0);
    PLL1CONbits.FSCMEN = 0; // disable clock fail monitor
    VCO1DIVbits.INTDIV = 1; // 1:2 = 320MHz
    PLL1DIVbits.PLLFBDIV = 80; // VCO = 640 MHz
    PLL1DIVbits.PLLPRE = 1;
    PLL1DIVbits.POSTDIV1 = 4;
    PLL1DIVbits.POSTDIV2 = 1;
    PLL1CONbits.DIVSWEN = 1;
    while(PLL1CONbits.DIVSWEN == 1);
    PLL1CONbits.NOSC = 1; // FRC
    PLL1CONbits.OSWEN = 1;
    while(PLL1CONbits.OSWEN == 1);
    PLL1CONbits.FOUTSWEN = 1;
    while(PLL1CONbits.FOUTSWEN == 1);
    PLL1CONbits.PLLSWEN = 1;
    while(PLL1CONbits.PLLSWEN == 1);
    while(PLL1CONbits.CLKRDY == 0);
    CLK1CONbits.NOSC = 5; // PLL1
    CLK1CONbits.OSWEN = 1;
    while(CLK1CONbits.OSWEN == 1);
    while(CLK1CONbits.CLKRDY == 0);
    // ADC high speed clock (Generator 6), should be 320 MHz for 80MHz operation
    CLK6CONbits.ON = 1;
    CLK6CONbits.NOSC = 7; // PLL1 VCO divider
    CLK6CONbits.OSWEN = 1;
    while(CLK6CONbits.OSWEN == 1);
    while(CLK6CONbits.CLKRDY == 0);
}