dsPIC30f ADC problem

[mshrestha789]

Hello friends,

Recently I've been working on dspic30f2010. I've written a code and displayed it in Terminal. But I am not getting the correct value. Even when I give 0v at the adc input pin, I get digital value around 10 instead of 0. Please help me regarding this.

I am posting initialization code of ADC. Here I have configure ADC for 1MSPS.

void ADC_Init(void){
		unsigned char val=0;
        ADCON1bits.FORM = 0x0;//signed fractional format
        ADCON1bits.SSRC = 0x7;//enable auto convert option
        ADCON1bits.ASAM = 0x1;//enable automatic sampling
        ADCON1bits.SIMSAM = 0;//enabble sequential sampling
        ADCON2bits.SMPI = 0x01;//Interrupts at the completion of conversion for each 2nd sample/convert sequence
        ADCON2bits.CHPS = 0x01;//sample on 2 S/H channels - CH0 and CH1
	
        ADCON3bits.SAMC = 0;//no Tad between start of sampling and start of conversion
        val = (unsigned char)(ADCS_VAL + 0.5);//Here 0.5 is added to get the rounding number
        ADCON3bits.ADCS = val;//configure A/D clock period

        ADCHS = 0x0023;//Set up A/D Channel Select Register to convert AN3 on Mux A input of CH0 and CH1 S/H amplifiers
        ADCSSL = 0x0000;//Channel Scanning is disabled. All bits left to their default state

        ADPCFG = 0xFFFF;
        TRISB |= (1<<3);//To set up AN3 as input
        ADPCFGbits.PCFG3 = 0;//Set up channels AN3 as analog input and configure rest as digital

        IFS0bits.ADIF = 0;//Clear the A/D interrupt flag bit
        IEC0bits.ADIE = 1;//Set the A/D interrupt enable bit
        ADCON1bits.ADON = 1;//Turn on the A/D converter
}

Any help regarding this will be highly appreciated.

 

[FvM]

To start with a simple thing, read the data sheet! Tad is specified with 12 minimum at 1 MS/s.

 

[mshrestha789]

Thanks for the reply.

Actually I forgot to add these lines in above code

_FOSC(CSW_FSCM_OFF & XT_PLL16);  //16x multiplier mode//XTAL = 7.3728 MHz
								//7.3728e+6*16/4 = 29.4 MIPS(Fcy)
                                
_FWDT(WDT_OFF);                 //Turn off the Watch-Dog Timer.
_FBORPOR(MCLR_EN & PWRT_OFF);   //Enable MCLR reset pin and turn off the power-up timers.
_FGS(CODE_PROT_OFF);            //Disable Code Protection

#define XTAL_OSC		7372800
#define FCY			(XTAL_OSC/4) * 16
#define TAD (float)1/((float)12 * (float)1000000)
#define ADCS_VAL		2 * TAD * FCY - 1

I have checked this in Mplab sim, it enters ADC's isr at desired time that is around 2us. It's the value of ADC (which i get in terminal) is not correct.

Please help me regarding this.

 

[Golden Electronics]

I think u select
ADCON2bits.CHPS = 0x01;//sample on 2 S/H channels - CH0 and CH1
so check setting & channel & required input for the setting is for both channel or Only for CH0 & Ch1 internally ground .....

 

[mshrestha789]

Actually I am setting up ADC for interrupting after 2 samples get filled in the buffer, for that I need to set up to sample on 2 S/H amplifiers. Also in their code example (form microchip), they are using the same configuration. So, ADCON2bits.CHPS = 0x01;
shouldn't be the problem.