The XIO instruction is commonly abbreviated for which phrase?

• A. Examine If Open
• B. Examine If Opened
• C. Examine If Off
• D. Exit Input

Answer: (A)

In ladder logic, XIO is the shorthand for testing the OFF state of an input. It stands for “Examine If Open.” This means the rung is true when the input contact is open (not energised), which is the inverse of the XIC instruction, “Examine If Closed,” that tests for a closed (ON) input. Use XIO when you want an action to occur only if the sensor is not active. The other phrases don’t fit the standard naming convention—“Opened” is not used here, “Off” isn’t the term in this acronym, and “Exit Input” isn’t a PLC term.