The SAADC peripheral can use several reference voltages (VREF), which are controlled in the REFSEL field of the register CH[n].CONFIG.
The accepted VREF voltages are the following:
- Internal reference, VREF=1.35 V
- External reference (0.4 V up to VDD) , VREF provided by the EXTREF pin
- VDD
The input from AIN[0..7] cannot exceed VDD or be lower than VSS. The input ranges are also limited by the REFERENCE used.
The following condition must always hold true for valid measurements, otherwise SAADC will saturate and report the max value determined by the RESOLUTION.
[V(P) - V(N) ] * 1/REFERENCE ≤ 1