This guidebook is a commentary written for those who will use the GX Developer version 8 software package (hereafter abbreviated to GX Developer) to create structured text (hereafter abbreviated to ST) programs for the first time.
"Chapter 1" introduces the overview of the ST language and the features of the ST language in the MELSEC-Q series.
"Chapter 2 to Chapter 6" introduce a series of basic operation methods, such as the methods of creating, debugging and saving programs in ST language through sample programs.
"Chapter 7" introduces useful functions available from GX Developer.
"Chapter 8" introduces the method of creating a program, which uses an ST-written function block (FB) in a ladder program from the main program created in ladder form, as an application program.
"Chapters 4, 5 and 8" use the PLC CPU for explanation
What Is ST Language ?
The ST language is defined in the International Standard IEC61131-3 that stipulates the logic description system in open controllers. The ST language supports operators, control syntaxes and functions to permit the following descriptions.
- Control syntaxes such as conditional sentence-dependent selective branch and repetitive sentence-based repetition
- Description of comments
- Expressions using operators (*, /, +, -, <, >, =, etc.)
- Call of user-defined function blocks (FB)
- Call of functions (MELSEC functions, IEC functions)
What Are the Features ?
The following introduces the main features of ST programs in the MELSEC-Q series.
Design efficiency improved by defining processings as parts.
With often used processings defined as parts in the form of function blocks (FB) in ST language, they can be used in necessary areas of each program.
This not only enhances the efficiency of program development but also reduces program mistakes, improving program quality.
Program change during system operation (online change).
Part of a running program can be changed without the PLC CPU being stopped.
Connection with other language programs.
Since other languages than the ST are also supported, the language adequate for processing can be used to increase the efficiency of program development. For example, write sequence control in a ladder program, and operation processing in ST language. Multiple languages support widespread application under optimum control.
A wealth of functions available.
The MELSEC functions compatible with various common instructions for the MELSEC-Q series and the IEC functions defined in IEC61131-3 are available for ST programs.
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