What is Examine if open (XIO) Instruction in PLC?

Use the Examine if open (XIO) instruction in your ladder program to determine if a bit is off.

  • When the XIO instruction is executed, if the bit addressed is on (1), then the instruction is evaluated as FALSE.

  • When the XIO instruction is executed, if the bit addressed is off (0), then the instruction is evaluated as TRUE.

Alternate name: Normally closed contact.

Examine if open (XIO) instruction

An XIO instruction inverts the state of the bit it references.

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