Structured Text

Structured Text (ST) is a high-level, text-based programming language defined in the IEC 61131-3 standard that brings the power and flexibility of traditional computer programming to industrial automation. Resembling Pascal or C in syntax, ST enables PLC programmers to implement complex algorithms, mathematical calculations, and data manipulation tasks that would be cumbersome or impossible to express in graphical languages like Ladder Logic or Function Block Diagrams. This powerful language has become increasingly important as modern automation systems require sophisticated control strategies, data processing capabilities, and integration with information technology systems.

The syntax and structure of Structured Text provide a rich set of programming constructs familiar to software developers while maintaining the deterministic execution required for industrial control. ST supports all standard data types including BOOL, INT, REAL, STRING, and complex structures, along with arrays and user-defined types for organizing data. Control flow statements such as IF-THEN-ELSE, CASE, FOR, WHILE, and REPEAT enable implementation of conditional logic and iterative processes. The language includes comprehensive operators for arithmetic, comparison, logical operations, and bit manipulation. Functions and function blocks can be defined and called with parameters, promoting code reuse and modular programming.

Structured Text excels in applications requiring complex mathematical processing, string manipulation, or algorithmic logic that would result in unwieldy ladder diagrams. Process control applications leverage ST for implementing advanced control algorithms like model predictive control, fuzzy logic, or custom PID variants. The integration of Structured Text within modern PLC programming environments has elevated it from a specialized tool to a mainstream development option. As automation systems increasingly incorporate IT technologies and require integration with enterprise systems, Structured Text serves as a bridge between operational technology and information technology.