Outputs are split into two main groups:
- NPN outputs are open collector. In this case, an external supply and pull-up resistor must be supplied.
- PNP outputs are open-emitter. In this case, an external ground and pull-down resistor must be supplied.
The voltage supply and resistor value will depend on the current and voltage specification of the output.
An issue that users run into is that the voltage difference between the high and low state on the output is not high enough. This is due to the choice of the resistor value. Note that the voltage drop across the output will increase or decrease depending on the resistor (V=IR).