A User Defined Function is a sequence of statements which may return an optional value.
A function that returns a value can be called from an Expression.
A function that does not return a value can be called through a Structured Text Function Call.
A Function uses the following syntax:
Function name [ : return-type ] variable-declarations statement; statement; ... statement; End_Function
Where:
A function to calculate the standard deviation of four values:
Function CalcStdDev : LREAL var_input v1,v2,v3,v4 : LREAL; end_var var SumOfSquares : LREAL; Mean : LREAL; end_var (* Calculate the mean *) Mean := (v1 + v2 + v3 + v4) / 4; (* Calculate the standard deviation *) SumOfSquares := (v1 - Mean) ** 2 + (v2 - Mean) ** 2 + (v3 - Mean) ** 2 + (v4 - Mean) ** 2; CalcStdDev := sqrt( SumOfSquares / 4 ); End_Function
Table 20a - IEC 61131-3 Second Edition.
Table 19 - IEC 61131-3 Third Edition.
To learn about other program units.
To learn about variable declarations.
Structured Text (ST) Statements
To learn about Structured Text (ST) Statements.
For the meaning of terms used in Fernhill SCADA.