– 18 – 61131-3 IEC:2003(E)
1.4.3 Programming model
The elements of programmable controller programming languages, and the subclauses in which they
appear in this part, are classified as follows:
Data types (2.3)
Variables (2.4)
Program organization units (2.5)
Functions (2.5.1)
Function blocks (2.5.2)
Programs (2.5.3)
Sequential Function Chart (SFC) elements (2.6)
Configuration elements (2.7)
Global variables (2.7.1)
Resources (2.7.1)
Access paths (2.7.1)
Tasks (2.7.2)
As shown in figure 3, the combination of these elements shall obey the following rules:
1) Derived
data types shall be declared as specified in 2.3.3, using the standard data types specified
in 2.3.1 and 2.3.2 and any previously derived data types.
2) Derived
functions can be declared as specified in 2.5.1.3, using standard or derived data types,
the standard functions defined in 2.5.1.5, and any previously derived functions. This declaration
shall use the mechanisms defined for the IL, ST, LD or FBD language.
3) Derived
function blocks can be declared as specified in 2.5.2.2, using standard or derived data
types and functions, the standard function blocks defined in 2.5.2.3, and any previously derived
function blocks. This declaration shall use the mechanisms defined for the IL, ST, LD, or FBD
language, and can include Sequential Function Chart (SFC) elements as defined in 2.6.
4) A
program shall be declared as specified in 2.5.3, using standard or derived data types, functions,
and function blocks. This declaration shall use the mechanisms defined for the IL, ST, LD, or FBD
language, and can include Sequential Function Chart (SFC) elements as defined in 2.6.
5)
Programs can be combined into configurations using the elements defined in 2.7, that is, global
variables, resources, tasks,
and access paths.
Reference to “previously derived” data types, functions, and function blocks in the above rules is
intended to imply that once such a derived element has been declared, its definition is available, for
example, in a “library” of derived elements, for use in further derivations. Therefore, the declaration of
a derived element type shall not be contained within the declaration of another derived element type.
A programming language other than one of those defined in this standard may be used in the
declaration of a
function or function block. The means by which a user program written in one of the
languages defined in this standard invokes the execution of, and accesses the data associated with,
such a derived function or function block shall be as defined in this standard.
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