Automatic control function programming manual ladder language

16.4 Programming in C
16.4.1 Concept of Module
Programming in C Language
A module is a separate executable entity. All the objects defined in a module (data or functions) are internal and can
be made available to external entities (C modules, ladder modules or monitor).
To be valid, a module must have a single «main()» function.
A module is the result of compiling and link editing of one or more source files in C. It is visible and accessible under
PLCTOOL as a «*.XCX» type file.
An application can include one or more C modules. It is strongly recommended to split large applications into several
modules.
16.4.2 Interface between C Modules
Applications written in C can be very large (several hundred Kbytes).
After editing the application, it is necessary to compile, link edit and load the entire module. The time required for these
operations can rapidly become very long.
To optimise the processing times, it is necessary to split large modules into several independent smaller modules that
can exchange all types of data (functions, tables, structures, variables).
In this way, a module works on pointers to the objects to be transferred and the pointers are initialised when the links
are edited.
Below we use the following terms:
- «imported object» to denote the objects used in a module and defined in another,
- «exported object» to denote objects defined in a module and made available to other modules.
An object can be any type of global data:
- Structure,
- Function,
- Global variable,
- Array,
- etc.
Two functions, IMPORT() and EXPORT(), are available for processing imported and exported objects.
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