USB-I/O Interface Adapter GPIO-24. Programmer's Reference Manual.
Chapter 7. Analog Inputs (ADC Module)
USB-I/O interface adapter ADC module allows conversion of an analog input signal to the corresponding 10-bit digital number. The result is generated via successive approximation. The analog-to-digital conversion can be represented mathematically as:
where:
ADCCode – ADC digital output code;
VIn – analog input voltage;
VRefHi – upper reference voltage;
VRefLow – lower reference voltage.
For more detailed information about the reference voltage see Section 7.3, “Analog Reference Voltage”.
We get much simpler expression when VRefLow is equal to zero:
If VRefHi = 5V and VRefLow = 0, analog-to-digital conversion can be illustrated by the following diagram:
