Iec 61131-3 Second edition 2003-01 Programmable controllers – Part 3: Programming languages

Figure 5 - Use of formal argument names
Features for the textual invocation of functions are defined in table 19 a). The textual invocation of a
function shall consist of the function name followed by a list of arguments. In the ST language defined
in subclause 3.3, the arguments shall be separated by commas and this list shall be delimited on the
left and right by parentheses.
In feature 1 of table 19 a) (formal invocation), the argument list has the form of a set of assignments of
actual values to the formal argument names (formal argument list), that is:
1) assignments of values to input and in-out variables using the ":=" operator, and
2) assignments of the values of output variables to variables using the "=>" operator.
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61131-3 
 IEC:2003(E)
– 49 –
The ordering of arguments in the list shall be insignificant. In feature 1 of table 19 a), any variable not
assigned a value in the list shall have the default value, if any, assigned in the function specification,
or the default value for the associated data type.
In feature 2 of table 19 a) (non-formal invocation), the argument list shall contain exactly the same
number of arguments, in exactly the same order and of the same data types as given in the function
definition, except the execution control arguments EN and ENO.
Table 19 a) - Textual invocation of functions for formal and non-formal argument list
Feature
Example
No.
Invocation
type
Variable
assignme
nt
Variable