Naming - References - SIMATIC AX - Support documentation - ST Style Guide, Cheat sheet

For a unique look, identifier should be named consistently in the project.

Rule:

Don't add prefixes to your identifier (Hungarian notation). Structured text is a strongly typed language, so they are not needed. Do not mark temporary values or internal values either.

wStw1       : WORD    //Not OK
Stw1        : WORD    //OK
r32SetPoint : REAL    //Not OK
SetPoint    : REAL    //OK

Exception: Interfaces should start with the capital letter I. The following letter of the identifier is capital.

Rule:

Abbreviations in names should be handled like a word and not written in capital letters, except the abbreviation consists of two characters. In this case, both letters may be capital.

VAR_GLOBAL
    IceTrainNumber  : INT;          //OK
    ICETrainNumber  : INT;          //Not OK
    DrivePNName     : STRING;       //OK
END_VAR

INTERFACE IHmiDeviceTemplate //OK

Rule:

Use PascalCasing for naming your PROGRAM, CLASS, METHOD, FUNCTION_BLOCK, FUNCTION, ENUM, STRUCT, VAR_GLOBAL and VAR_PUBLIC: First letter of every word in the name with a capital letter, the rest of the word in lower case. Do not use any separation characters like underscores _ or hyphens -

VAR_GLOBAL
    ActualSpeed     : REAL;         //OK
    Actual_Speed    : REAL;         //Not OK
    _actualSpeed    : REAL;         //Not OK
END_VAR
FUNCTION    CalcRotorSpeed          //OK
CLASS       binarySignal            //Not OK

Rule:

Use _camelCasing with a leading underscore _ for private variables in the sections VAR PRIVATE, VAR PROTECTED and VAR: Do not use any separation characters like hyphens - and do not use underscores _ inside the name.

Variables inside the VAR section in methods and functions behave like VAR_TEMP. In those sections, the rule for VAR_TEMP applies instead.

VAR
    _actualSpeed     : REAL;         //OK
    _actual_Speed    : REAL;         //Not OK
    actualSpeed      : REAL;         //Not OK
END_VAR

Rule: Use camelCasing for your IO variables and temporary variables in the sections VAR_INPUT, VAR_OUTPUT, VAR_IN_OUT and VAR_TEMP: Do not use any separation characters like underscores _ or hyphens -

VAR_INPUT
    actualSpeed     : REAL;         //OK
    ActualSpeed     : REAL;         //Not OK
END_VAR

Rule:

Use SNAKE_CASING (All capital letters with underscores dividing words) in symbolic constants and for enumeration values.

VAR CONSTANT
    NUMBER_OF_DRIVES : INT := 5; //constant definition
END_VAR
TYPE
    ModeType : (
        BUSY,
        FREE,
        RUN
    ); //enumeration definition
END_TYPE

Recommendation:

The name of an identifier indicates its meaning and purpose. Avoid names like i or j. For identifiers consisting of several words, the sequence of the words should be selected like that in spoken language.

Recommendation:

Avoid using very long identifier names. 32 characters should not be exceeded.

Recommendation:

The name in the identifiers should be in English.

Recommendation:

The name of an array is always in the plural.

VAR
    AxesPos : Array[0..5] OF AxisPosition //OK
    AxisPos : Array[0..5] OF AxisPosition //Not OK
END_VAR

Recommendation:

Avoid a name for the identifier that is similar to keywords of ST.(e.g. 'Classes', 'FunctionBlock', 'Functions').

Recommendation:

Avoid a name for the identifier that is equal to a keyword of another widely used programming language. (e.g. C#: 'foreach', 'void').

Recommendation:

Use abbreviations only for common words. If you use an abbreviation, its meaning should never be ambiguous.

Here are some common abbreviations you should use: