The purpose of the discrete input module is to read the status of field devices which have just two states:  On or off.

When a voltage is detected on the terminal of an input module with respect to common, the corresponding status light is energized, and during the processor scan, the value of 1 is placed into the controller tag for that module.  An example of a tag address for an input module would be:  Local:5:I.Data.0  (The Local Chassis (where the processor resides that this project is for)  Slot 5, Terminal 0)

Examples of input devices include switches, pushbuttons, or auxiliary contacts on a motor starter.

The Removable Terminal Block (RTB) can be detached from the module if the locking tab is pushed up (into the unlocked position) The enclosure of the RTB will also slide off the terminal block for easy access to the terminals.

A wide variety of Input Modules can be used such as AC or DC modules, Isolated or Non-Isolated, and Diagnostic modules which can detect an open circuit by placing a resistor across each switch wired to the input module.