Structured Text (ST), Extended Structured Text (ExST)

The ST editor is used for the programming of POUs in the IEC 61131-3 programming language Structured Text (ST) and Extended Structured Text. The Extended Structured Text offers some additional functions with regard to the IEC 61131-3 standard.

Structured Text is a programming language, comparable with other high-level languages such as C or PASCAL, which permits the development of complex algorithms. The program code consists of a combination of expressions and statements, which can also be executed conditionally (IF…THEN…ELSE) or in loops (WHILE…DO).

An expression is a construct that returns a value following its evaluation. Expressions are also operators and operands together. You can also use assignments as expressions. An operand can be a constant, variable, function call, or another expression.

Instructions control how the expressions are to be processed.

For this text editor you can make various settings with regard to behavior, appearance and menus in the dialogs Options and Adapt in the Tools menu. The familiar Windows functions (for example IntelliMouse) are also available for this editor.

For more information, see: Programming in Structured Text (ST)

ExST – Extended Structured Text

Extended Structured Text (ExST) is a CODESYS-specific extension based on the IEC 61131-3 standard for Structured Text (ST).

For more information, see: Assignments