ADC Conversion Procedure

This is an example procedure for using the ADC to perform an analog-to-digital conversion:

1.Configure port:
1. a.Disable the pin output driver (refer to the TRISx register)
2. b.Configure the pin as analog (refer to the ANSELx register)
2.Configure the ADC module:
1. a.Select the ADC conversion clock
2. b.Configure the voltage reference
3. c.Select the ADC input channel
4. d.Configure result format
5. e.Turn on the ADC module
3.Configure ADC interrupt (optional):
1. a.Clear the ADC interrupt flag
2. b.Enable the ADC interrupt
3. c.Enable the peripheral interrupt (PEIE bit)
4. d.Enable the global interrupt (GIE bit)⁽¹⁾
4.Wait the required acquisition time⁽²⁾
5.Start conversion by setting the GO bit
6.Wait for ADC conversion to complete by one of the following:
- Polling the GO bit
- Waiting for the ADC interrupt (if interrupt is enabled)
7.Read ADC Result
8.Clear the ADC interrupt flag (if interrupt is enabled)

Notes:

1.With global interrupts disabled (GIE = 0), the device will wake from Sleep but will not enter an Interrupt Service Routine.
2.Refer to ADC Acquisition Requirements for more details.

ADC Conversion (assembly)

; This code block configures the ADC for polling,
; V_DD and V_SS references,
; ADCRC oscillator, and AN0 input.
; Conversion start & polling for completion are included.

    BANKSEL TRISA
    BSF     TRISA,0     ; Set RA0 to input
    BANKSEL ANSEL
    BSF     ANSEL,0     ; Set RA0 to analog
    BANKSEL ADCON0
    CLRF    ADCON0
    CLRF    ADCON1
    CLRF    ADACT       ; Auto-conversion disabled
    BSF     ADCON0,0    ; CHS = RA0, ADC ON
    MOVLW   B’11110000’ ; FM = Right-justified, CS = ADCRC, PREF = VDD
    MOVWF   ADCON1
    CALL    SampleTime  ; Acquisition delay
    BANKSEL ADCON0
    BSF     ADCON0,GO   ; Start conversion
    BTFSC   ADCON0,GO   ; Is conversion done?
    GOTO    $-1         ; No, test again
    BANKSEL ADRESH
    MOVF    ADRESH,W    ; Read upper byte
    MOVWF   RESULTHI    ; Store in GPR space
    MOVF    ADRESL,W    ; Read lower byte
    MOVWF   RESULTLO    ; Store in GPR space

ADC Conversion (C)

/*This code block configures the ADC
for polling, V_DD and V_SS references,
ADCRC oscillator and AN0 input.
Conversion start & polling for completion
are included.
  */
    void main() {
        //System Initialize
        initializeSystem();

        // Configure Port
        TRISAbits.TRISA0 = 1;      // Set RA0 to input
        ANSELAbits.ANSELA0 = 1;    // Set RA0 to analog

        // Configure ADC
        ADCON1bits.CS = 1;         // ADCRC Clock
        ADCON1bits.PREF = ‘b11;    // V_DD
        ADCON0bits.CHS = ‘b000000; // RA0
        ADCON1bits.FM = 1;         // Right justify
        ADCON0bits.ON = 1;         // Turn ADC On

    while (1) {
        ADCON0bits.GO = 1;         // Start conversion
        while (ADCON0bits.GO);     // Wait for conversion done
        resultHigh = ADRESH;       // Read result
        resultLow = ADRESL;        // Read result
    }
 }