Introduction to Structured Text Programming in RSLogix and Studio 5000 Allen Bradley

Introduction

As you develop your skillset in PLC programming, you’ll realize that there are many ways to accomplish the same task. However, certain approaches would be much more applicable in certain cases and less so in others. Through ladder logic, you can create programs that are easy to maintain, understand, and augment over time. That being said, most PLCs, including Allen Bradley ones, offer other ways of implementing logic. These different ways of programming are as follows: Structured Text [ST], Function Block Diagrams [FBD], and Sequential Function Charts [SFC].

The advantage of using structured text over ladder logic isn’t always apparent. It’s typically hard to transition into structured text after investing time in learning ladder logic. In contrast, those who are coming into PLC programming with a background in software engineering may found it easier to understand than ladder logic. In fact, the structure in ST is much closer to a traditional programming language such as C, C++, Java, or Python than it is to ladder logic.

An implementation in structured text allows the programmer to create complex routines and flows that may not always be as easily implemented in ladder logic. For example, a FOR loop would take a single line of code to implement in ST while it requires a separate routine in ladder logic. Furthermore, it’s also possible to leverage string manipulation through Excel in order to…