Differential input is a input method in which the signal source is connected
by three signal lines.
The three signal lines are ground line, signal line(+) and signal line(-)
respectively.
The input data is the difference between the voltage (A) between the ground
line and the signal line(+) and the voltage (B) between the ground line
and the signal line(-), that is the value of A-B which is AD converted
as the input voltage.