the ground, the digital output is about 6600, and if using multimeter to
measure V1-V1GND, the voltage is about 1.8V. Is this normal? Also, if V1 and
V1GND are both connected to GND, the ADC result is 0.
the input is floating then we cannot predict where the voltage level is at.
Floating inputs is not a condition we recommend. If the inputs are unused they
should be tied off to GND.