SAM C21 Xplained Pro has a 6-pin header labeled VREF on the board. This header can be used to select / apply a voltage reference to the ADC, DAC, and SDADC. Jumpers can be used to tie SADC VREF and ADC/DAC VREFT to the kit target voltage from pin 1-3 and 2-4, or external voltages can be applied across pin 3-5 and 4-6.
| VREF header pin | Pin / Net | Function |
|---|---|---|
| 1 | VCC_AREF_P3V3_P5V0 | Filtered kit target voltage |
| 2 | VCC_AREF_P3V3_P5V0 | Filtered kit target voltage |
| 3 | PA04 | SDADC voltage reference |
| 4 | PA03 | ADC / DAC voltage reference |
| 5 | GND | Ground |
| 6 | GND | Ground |