ADC: The argument of vref=num is an integer. Values for num are:
SAMD21:
0 INT1V 1.0V voltage reference
1 INTVCC0 1/1.48 Analog voltage supply
2 INTVCC1 1/2 Analog voltage supply (only for VDDANA > 2.0V)
3 VREFA External reference
4 VREFB External reference
SAMD51:
0 INTREF internal bandgap reference
1 INTVCC1 Analog voltage supply
2 INTVCC0 1/2 Analog voltage supply (only for VDDANA > 2.0v)
3 AREFA External reference A
4 AREFB External reference B
5 AREFC External reference C (ADC1 only)
DAC: The argument of vref=num is an integer. Suitable values:
SAMD21:
0 INT1V Internal voltage reference
1 VDDANA Analog voltage supply
2 VREFA External reference
SAMD51:
0 INTREF Internal bandgap reference
1 VDDANA Analog voltage supply
2 VREFAU Unbuffered external voltage reference (not buffered in DAC)
4 VREFAB Buffered external voltage reference (buffered in DAC).
