What is the primary purpose of the XIC instruction in PLC programming?

The primary purpose of the XIC instruction, which stands for "Examine If Closed," is to check the status of an input in PLC programming. This instruction evaluates the condition of a specified input or memory bit, determining whether it is in a closed (true) state or an open (false) state. When the input is in the closed state, the XIC instruction allows the program to continue executing the following instructions in the rung. This is fundamental in ladder logic design, as it is used to determine whether certain conditions are met in order to proceed with control logic, such as operating outputs or triggering timers.

The identification and evaluation of inputs are critical in automated systems, as they often dictate the machinery's response and operational flow. By using the XIC instruction, programmers can establish conditions that must be satisfied for processes to occur, ensuring that the system behaves predictably in response to inputs like sensor states or user commands.