Pic18f4520 a/d

[yohanevindra]

In setting the A/D converter, its required to set ADCON2. In that register there are two sets of bits, namely the A/D acquisition time select bits and the A/D conversion clock select bits.

At the moment I'm using only one analog input, but later on my plan is to have about 3 analog inputs which would need to communicated with the computer. what are the ideal settings?

Also, what does "20Tad" mean in terms of acquisition time?

 

[be80be]

20Tad = 20 instruction cycles to acquisition

Here some sample In C for 18fX chips

unsigned int ADCResult=0;
float voltage=0;

void main(void)
{        

        unsigned char channel=0x00,config1=0x00,config2=0x00,config3=0x00,portconfig=0x00,i=0;

//----- clear adc interrupt and turn off adc if in case was on prerviously---------------                
        CloseADC();        

//-------------------------initialize adc---------------------------------------------------------------
/**** ADC configured for:
        * FOSC/2 as conversion clock
        * Result is right justified
        * Aquisition time of 2 AD
        * Channel 1 for sampling
        * ADC interrupt on
        * ADC reference voltage from VDD & VSS
*/
        config1 = ADC_FOSC_2 | ADC_RIGHT_JUST | ADC_2_TAD ;
        config2 = ADC_CH0 | ADC_INT_ON | ADC_REF_VDD_VSS ;
        portconfig = ADC_15ANA ;
        OpenADC(config1,config2,portconfig);


//------------------------------initialize the adc interrupt and enable them-------------------------------------        
        ADC_INT_ENABLE(); 

//-----------------------sample and convert-------------------------------- -------------------------
        for(i=0;i<16;i++)
        {
        ConvertADC();
    while(BusyADC());        
        ADCResult += (unsigned int) ReadADC();
        }
        ADCResult /= 16;
        voltage = (ADCResult*5.0)/1024; // convert ADC count into voltage
        
//----------------------------------------------------------------------------------------------------------- 
    CloseADC();                 //turn off ADC
        
        while(1);                                                //End of program 
}

 

[Wond3rboy]

Tad Stands for Acquisition time for the Analog to Digitla Converter. If you want to get familiar with the terminology, check this tutorial about ADCs by Microchip.

https://www.electro-tech-online.com/custompdfs/2010/11/adc-1.pdf