ADC p16F917

[mircea1981]

Hi.

I am a beginer in pic microcontroller and i need some help. I have a development board from Microchip, PICDEM Mechatronics with a pic16f917 microcontroller.
I use MPLAB IDE v8.70 and HI-TECH ANSI C Compiler.
In code if the current provided from a potentiometer is less than a threshold (2.5 V) the diode D0 must be ON, else OFF.

When i run the code in debug mode i receive the next error :
ADC-W0001: Tad time is less than 1.60us
ADC-W0008: No stimulus file attached to ADRESL for A/D.

I do not understand why i receive this error since the Fosc is 8MHz, AD conversion clock is 16.
So, with this setings i computed the
Tad = 2 microsec.

The code :

#include<pic.h>

__CONFIG(FCMEN_ON & IESO_OFF & CP_OFF & WDTE_OFF & BOREN_OFF & MCLRE_ON & PWRTE_OFF);

#define ZERO        0
#define ONE            1

unsigned int ADC_result;
unsigned char ADC_channel;

void Clock_Init(void)
{
   // Internal Oscillator Frequency Select bits - 8 MHz
    OSCCONbits.IRCF2 = ONE;
    OSCCONbits.IRCF1 = ONE;
    OSCCONbits.IRCF0 = ONE;
    // Set the ADC clock frequency Fosc/16 = 500 KHz
    ADCON1bits.ADCS2 = ONE;
    ADCON1bits.ADCS1 = ZERO;
    ADCON1bits.ADCS0 = ONE;
}

void Comparators_Init(void)
{
    // Comparators Off
    CMCON0bits.CM2 = ONE;
    CMCON0bits.CM1 = ONE;
    CMCON0bits.CM0 = ONE;
}

void Port_Init(void)
{
  // Pin RA3/AN3 is set input
    TRISAbits.TRISA3 = ONE;
    // Set RA3/AN3 to analog mode
    ANSELbits.ANS3 = ONE;

   // Set RD7 as an output
    TRISD = ZERO;
    PORTD = ZERO;
}

void ADC_Init(void)
{
    // A/D result left justified
    ADCON0bits.ADFM = ZERO;
    // +/- Vref.
    ADCON0bits.VCFG1 = ZERO;
    ADCON0bits.VCFG0 = ZERO;
    // Analog channel 3 selected
    ADCON0bits.CHS2 = ZERO;
    ADCON0bits.CHS1 = ONE;
    ADCON0bits.CHS0 = ONE;
    // Select ADC Channel
      ADC_channel = ADCON0bits.CHS;
    // Switch on the adc module
      ADCON0bits.ADON = ONE;
}

unsigned int ADCRead(void)
{
    // Start conversion
      ADCON0bits.GO = ONE;
    // Wait for the conversion to finish
      while(ADCON0bits.GO == ONE);
    ADC_result = (ADRESH<<8) + ADRESL;
    // Switch off adc
      ADCON0bits.ADON = ZERO;
 
      return ADC_result;
}

void main (void)
{
    Clock_Init();
 
    Comparators_Init();

    // Init port pins
    Port_Init();

      // Init ADC
      ADC_Init();

    // code will run in for loop forever
    for( ; ; )
    {
      // Read Channel 3
        ADC_result = ADCRead();
        if(ADC_result < 2.5)
        {
            PORTDbits.RD0 = ONE;
        }
        else
        {
            PORTDbits.RD0 = ZERO;
        }
    }
 
}

 

[Ian Rogers]

TAD timings will cause a warning.. Not an error..

The main issue here is... At the end of the ADC read you turn off the module.... Then never turn it back on..

ADCON0.ADON = 1; .. Then wait over 100nS... then ADCON0.GO = 1;