The Voltage Reference peripheral (VREF) provides control registers for the voltage reference sources used by several peripherals. The user can select the reference voltages for the ADC0 by writing to the ADC0 Reference Select bit field (ADC0REFSEL) in the Control A register (VREF.CTRLA), and for both AC0 and DAC0 by writing to the DAC0 and AC0 Reference Select bit field DAC0REFSEL in VREF.CTRLA.

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 Force Enable bit (ADC0REFEN, DAC0REFEN) in the Control B register (VREF.CTRLB). This may be desirable to decrease start-up time, at the cost of increased power consumption.