The XIO, also known as Examine If Open, instruction perform the function opposite to the XIC (Examine if Closed). It’s a fundamental instruction for working with Programmable Logic Controllers (PLCs). This instruction can be found on the left side of a ladder logic rung and will evaluate to true if the specified bit is set to a LOW state. If that’s the case, the instruction will allow the rest of the rung to execute.
This is a companion discussion topic for the original entry at https://www.solisplc.com/tutorials/plc-programming-fundamentals-xio-instruction