The function of the XIO instruction is to:

The function of the XIO instruction is to examine the status of a certain condition or input point, specifically checking if it is closed. This means that when the XIO instruction is used in a ladder logic diagram, it evaluates whether an associated input is not active or is in an open state. If the input condition is met (meaning it is "open"), the instruction allows the logic to proceed.

This behavior is essential in programmable logic controllers (PLCs) for controlling processes based on whether specific inputs are true or false, allowing for branching paths in control logic. Thus, the XIO instruction plays a critical role in monitoring conditions that can define the operational flow of the control system.

By recognizing the correct functionality of the XIO instruction, you can effectively utilize it in scenarios where you need to check for non-active states in your control applications.