ADC Single Conversion

The simplest mode of using the ADC is to make a single conversion. The ADC input pin needs to have the digital input buffer and the pull-up resistor disabled, in order to have the highest possible input impedance. Pin PD6/AIN6 is used for ADC input in this example.

ADC0.MUXPOS = ADC_MUXPOS_AIN6_gc;

The ADC Clock Prescaler can be used to divide the clock frequency. In this particular example, the clock is divided by 4. The ADC can use V_DD, external reference or internal reference for its positive reference. The internal reference is used in this example.

ADC0.CTRLC |= ADC_PRESC_DIV4_gc;
ADC0.CTRLC |= ADC_REFSEL_INTREF_gc;

The ADC resolution is set by the RESSEL bit in the ADC0.CTRLA register. The ADC is enabled by setting the ENABLE bit in the ADC0.CTRLA register.

ADC0.CTRLA |= ADC_RESSEL_10BIT_gc;
ADC0.CTRLA |= ADC_ENABLE_bm;

The ADC conversion is started by setting the STCONV bit in the ADC0.COMMAND register.

ADC0.COMMAND = ADC_STCONV_bm;

When the conversion is done, the RESRDY bit in the ADC0.INTFLAGS gets set by the hardware. The user must wait for that bit to get set before reading the ADC result.

while (!(ADC0.INTFLAGS & ADC_RESRDY_bm))
{
    ;
}

The user must clear the RESRDY bit by writing ‘1’ to it before starting another conversion.

ADC0.INTFLAGS = ADC_RESRDY_bm;

The conversion result can be read from the ADC0.RES register.

adcVal = ADC0.RES;