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ADC - Analog to Digital Conversion

The Analog-to-Digital (A/D) Converter module has five inputs for the 28-pin devices and eight for the 40/44-pin devices. The conversion of an analog input signal results in a corresponding 10-bit digital number. The A/D module has high and low-voltage reference input that is software selectable to some combination of VDD, VSS, RA2 or RA3. The A/D converter has a unique feature of being able to operate while the device is in Sleep mode. To operate in Sleep, the A/D clock must be derived from the A/D’s internal RC oscillator.

The A/D module has four registers. These registers are: - A/D Result High Register (ADRESH) - A/D Result Low Register (ADRESL) - A/D Control Register 0 (ADCON0) - A/D Control Register 1 (ADCON1)

Steps in A/D Conversion - Configure ADCON0 register to set the clock frequency, set up channels and powering up the A/D module. 

      ADCON0bits.ADCS = 0b00; // set A/D conversion clock = fosc/2
      ADCON0bits.CHS = 0b000; // set all adc channels off
      ADCON0bits.ADON = 0; // a/d module is powered off
- Configure ADCON1 to set the justification of 10bit output (Ouptut is stored in both ADRESH and ADRESL), clock frequency and data direction of analog input pins. 
      ADCON1bits.ADFM = 1; // set right justification for ADRESH
      ADCON1bits.ADCS2 = 0; // set A/D conversion clock = fosc/2
      ADCON1bits.PCFG = 0b0000; // set all pins as adc input
- Read analog input value 
      int __adc_read(int adc_channel) {
          ADCON0bits.ADON = 1; // turn on a/d module
          ADCON0bits.CHS = adc_channel; // turn on adc channel
          __delay_ms(10); // wait for capacitors to charge up
          ADCON0bits.GO = 1; // begin conversion
          while(ADCON0bits.GO_DONE == 1) {
              // wait for conversion to finish
          }
          int adc_value = (ADRESH << 8) + (ADRESL);
          return adc_value;
      }

Circuit Diagram

License

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This work is licensed under GNU General Public License v3.0.