How can you debug a PLC program in structured text?

2 Use breakpoints and watch variables

The second step to debug a PLC program in structured text is to use breakpoints and watch variables to monitor and control the execution of your code. Breakpoints are points in your code where you can pause the execution and inspect the values of the variables and the outputs of the functions. Watch variables are variables that you can select and display in a separate window to observe their changes during the execution. You can use breakpoints and watch variables to test the logic and the behavior of your code, to identify logical errors, and to verify the expected outcomes.

3 Use simulation and debugging modes

The third step to debug a PLC program in structured text is to use simulation and debugging modes to test your code without affecting the real PLC or the connected devices. Simulation mode is a mode where you can run your code on your computer without downloading it to the PLC. Debugging mode is a mode where you can run your code on the PLC and interact with it using your computer. You can use simulation and debugging modes to check the performance and the functionality of your code, to detect runtime errors, and to troubleshoot any issues.

4 Use comments and documentation

The fourth step to debug a PLC program in structured text is to use comments and documentation to explain and organize your code. Comments are lines of text that are ignored by the PLC software or compiler, but that can help you and others to understand the purpose and the logic of your code. Documentation is a separate file or document that describes the structure, the features, and the requirements of your code. You can use comments and documentation to make your code more readable, maintainable, and reusable, and to avoid confusion and ambiguity.

5 Use standard and consistent coding style

The fifth step to debug a PLC program in structured text is to use standard and consistent coding style to write your code. Coding style is a set of rules and conventions that define how to format, name, and structure your code. Using standard and consistent coding style can help you to avoid syntax and semantic errors, to improve the clarity and the quality of your code, and to follow the best practices and the recommendations of the IEC 61131-3 standard. You can use standard and consistent coding style to make your code easier to debug, modify, and share.

6 Use modular and testable code

The sixth and final step to debug a PLC program in structured text is to use modular and testable code to design your code. Modular code is code that is divided into smaller and independent units, such as functions, programs, or libraries, that can be reused and combined. Testable code is code that can be verified and validated using different methods, such as unit testing, integration testing, or system testing. You can use modular and testable code to reduce the complexity and the size of your code, to increase the reliability and the efficiency of your code, and to simplify the debugging process.