PLC Programming Fundamentals - XIC Instruction

Introduction

The XIC, also known as Examine If Closed, instruction is one of the fundamental instructions used in ladder logic programming for Programmable Logic Controllers (PLCs). This instruction is always found on the left side of a ladder rung and will verify if the specified bit is in a logic HIGH state. If that’s the case, the instruction will evaluate to true and allow the rest of the rung to execute.

Example & Usage of XIC

Here’s a real-world scenario of an XIC instruction:

1. A Micrologix 1100 Allen Bradley PLC is used to control a process.
2. A normally open push button (“System Start”) is connected to Input 0 (I0/0 of the PLC).
3. An operator presses the button.
4. The XIC instruction is tied to I0/0.
5. The XIC instruction evaluates to TRUE while the button is pressed.
6. The XIC instruction evaluates to FALSE while the button is released.

Programming example in RSLogix 500:

Data Types Allowed for XIC

The XIC instruction will work with the following data types within the RSLogix 500 environment:

• Boolean – The XIC may only evaluate TRUE/FALSE or 1/0 or HIGH/LOW.

Important Notes

• Note 1 – The XIC instruction was initially used to evaluate the status of inputs landed on the PLC. However, it may be used on any boolean within the program. In other words, it can examine if any boolean within the program is energized. This makes the XIC instruction powerful and versatile.