#include <p32xxxx.h>
#include <plib.h>
//#include <xc.h>
// configuration bit settings, Fcy=72 MHz, Fpb=36 MHz
#pragma config POSCMOD=XT, FNOSC=PRIPLL
#pragma config FPLLIDIV=DIV_2, FPLLMUL=MUL_18, FPLLODIV=DIV_1
#pragma config FPBDIV=DIV_2, FWDTEN=OFF, CP=OFF, BWP=OFF
#define POT 8 // 10 k potentiometer
#define AINPUTS 0xff7f // Analog inputs POT, TSENS
void initADC( int amask)
{
AD1PCFG = amask; // select analog input pins
AD1CON1 = 0x00E0; // automatic conversion after sampling
AD1CSSL = 0; // no scanning required
AD1CON2 = 0; // use MUXA, use AVdd &AVss as Vref+/-
AD1CON3 = 0x1F3F; // Tsamp = 32 x Tad;
AD1CON1bits.ADON = 1; // turn on the ADC
} //initADC
int readADC( int ch)
{
AD1CHSbits.CH0SA = ch; // 1. select input channel
AD1CON1bits.SAMP = 1; // 2. start sampling
while (!AD1CON1bits.DONE); // 3. wait conversion complete
return ADC1BUF0; // 4. read conversion result
} // readADC
void DelayMs(unsigned int msec)
{
unsigned int tWait, tStart;
tWait=(80000000/2000)*msec;
tStart=ReadCoreTimer();
while((ReadCoreTimer()-tStart)<tWait); // wait for the time to pass
}
main ()
{
int i, a;
// initializations
initADC( AINPUTS); // initialize the ADC
// main loop
while( 1)
{
a = readADC(8); // select the POT input and convert
} // main loop
} // main
In addition, you are perhaps not providing enough time to internal A/D capacitance to hold sampled value.
int analogRead(char analogPIN)
{
AD1CON1 = 0x000000E0;
AD1CHS = 0;
AD1CSSL = 0;
AD1CON2 = 0x00000000;
AD1CON3 = 0x00001F00;
AD1CON1bits.ADON = 1;
AD1CHS = analogPIN << 16; // AD1CHS<16:19> controls which analog pin goes to the ADC
//AD1CON1bits.SAMP = 0;
AD1CON1bits.ASAM = 1;
delay_ms(500);
while (!IFS0bits.AD1IF);
IFS0bits.AD1IF = 0;
//AD1CON1bits.SAMP = 1;
AD1CON1bits.DONE = 0; // wait until conversion done
return ADC1BUF0; // result stored in ADC1BUF0
}