Introduction

The ST editor is used for programming in structured text according to IEC 61131-3.

Representation

Representation of an ST section:

Objects

The ST programming language works with "Expressions".

Expressions are constructions consisting of operators and operands that return a value when executed.

Operators are symbols representing the operations to be executed.

Operators are used for operands. Operands are variables, literals, function and function block inputs/outputs etc.

Instructions are used to structure and control the expressions.

Input Aids

The ST editor offers the following input aids:

• Syntax and semantics are checked as the program is being written.

  • Keywords and comments are displayed in color

  • Unknown words (e.g. undeclared variables) or unsuitable data types are marked with a red wavy line

  • Brief description of errors in the Quickinfo (Tooltip)

• Tabular display of the functions and function blocks

• Input assistance for functions and function blocks

• Operands can be entered and displayed as symbols or topological addresses

• Display of inspection windows