This article describes the editing operation for the structured text (ST) of the GX Developer Ver 8 software package.
What Is the ST Language?
The ST language is described in the IEC61131-3 International Standard that specifies the logic explanation system in open controllers. The ST language carries operators, control functions and syntaxes to allow the following explanations.
Control syntaxes for example conditional sentence-dependent discerning branch and recurring sentence-based recurrence. Expressions with operators (-, <, >, =, *, /, +, etc.)
• Call of user-described FB (function blocks)
• Functions Call (functions IEC, functions MELSEC)
The major features of the ST language are as explained as following.
1. Free explanation in format of text
The ST language lets the alphanumeric characters description, labels and comments in format of text.
2. Programming on the similar level as of the C language and other high level languages
Like the high level languages for example C, the ST language can explain control with syntaxes control such conditional sentence-dependent discerning branches and recurring sentence-based recurrences. Therefore, easy to read programs can be written temporarily.
3. Simplicity of telling operation processing
Accomplished of temporarily describing easy-to-read operation processing that are hard to explain in lists or ladders, the ST language has a program readability high level of and is appropriate for the fields where complicated comparison operations, arithmetic operations, etc. are carried out.
ST programs are explained in ST language. Making ST programs with GX Developer allows efficient programming to be executed in outstanding operation environment. The following offers the key features of ST programs in the series of MELSEC-Q.
1. Design effectiveness enhanced by defining processing as parts
With frequently used processing described as parts in the function blocks (FB) form in ST language, they can be utilized in required areas of every program. This not only improves the program development efficiency but also decreases program errors, improving quality of program.
2. Program modify during operation the system (online change)
A running program part can be adjusted with no the PLC CPU being stopped.
3. Link with other programs language
The language sufficient for processing can be utilized to enlarge the program development efficiency since the ser of as MELSEC-Q also supports languages other than the ST. The model QCPU and Process QCPU high performance permit implementation conditions to be set on a file basis, and multiple files of program to be written to a single PLC CPU. The multiple languages support extensive application under most favorable control.
4. available in a wealth of functions
The functions of MELSEC well-matched with a variety of common instructions for the series of MELSEC-Q and the IEC functions specified in IEC61131-3 are accessible for ST programs in the series of MELSEC-Q.