The Voltage Reference (VREF) peripheral provides control registers for the voltage reference sources used by several peripherals. The user can select the reference voltages for the ADC0, DAC0 and ACs by writing to the appropriate registers in the VREF peripheral.
A voltage reference source is enabled automatically when requested by a peripheral. The user can enable the reference voltage sources, and thus, override the automatic disabling of unused sources by writing to the respective ALWAYSON bit in VREF.ADC0REF, VREF.DAC0REF and VREF.ACREF. This will decrease the start-up time at the cost of increased power consumption.