PLC inputs are easily represented in ladder logic. In below Figure there are three types of inputs shown.
Figure: Ladder Logic Inputs
The first two are normally open and normally closed inputs, discussed previously.
The IIT (Immediate InpuT) function allows inputs to be read after the input scan, while the ladder logic is being scanned.
This allows ladder logic to examine input values more often than once every cycle.
(Note: This instruction is not available on the ControlLogix processors, but is still available on older models.)