Structured Text Programming in PLC

PLCs (Programmable Logic Controllers) provide a high-level text-based language for control logic programming called Structured Text (ST) programming. It provides an organized method for developing code, which facilitates the organization and maintaining of complex control systems.

Overview of PLC structured text programming:


The syntax of ST is similar to that of the Pascal programming language, with operators and keywords for functions, data types, and control structures.

Data Types

ST is capable of handling a wide range of data kinds, including character strings, INT, REAL, Boolean, and more.

Control Structures

For implementing decision-making and repeated operations, ST permits the use of control structures such as IF…THEN…ELSE, CASE, WHILE, REPEAT…UNTIL, & FOR loops.

Functions and Function Blocks

For code modularity and reusability, it facilitates the design of reusable functions & function blocks, that include particular logic or algorithms.

Mathematical Operations

Complex computations are made possible by ST’s built-in mathematical operators & functions for arithmetic, comparison, & logical operations.

Data Manipulation

ST provides robust data manipulation features, including as bitwise operations, string handling, assignments, and array operations.

Error Handling

PLC programs can be made robust and fault-tolerant by utilizing structured error handling with TRY…END_TRY & other error-handling components.

Real-Time Execution

Because ST programs run on PLCs in real-time, they are appropriate for time-sensitive control applications that need exact timing and responsiveness.

Debugging and Testing

PLC development environments facilitate code validation & troubleshooting by offering debugging tools for ST code, such as breakpoints, online monitoring, and diagnostic messages.


When combined with other PLC-supported programming languages like ladder logic (LD) (or) function block diagram (FBD), ST enables developers to select the best language for a given task inside a project.

Overall, structured text programming in PLCs provides flexibility, readability, and scalability, making it the preferred method for creating sophisticated control algorithms & applications in industrial automation.