Functions

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Introduction

A function is a section of code that can be called by another part of a program or script.

In the Fernhill SCADA implementation of IEC 61131-3 there are three groups of functions:

Standard Functions - functions that are built in to the language that return a single value.
Extension Functions - functions that are built in but are an extension to the IEC 61131-3 standard.
User Defined - functions declared by the user that can return no value, a single value, or multiple values.

EN and ENO

In IEC 61131-3, all functions have the following two variables implicitly declared:

VAR_INPUT EN : BOOL := TRUE; END_VAR
VAR_OUTPUT ENO : BOOL; END_VAR

If the EN parameter is FALSE, the function body is skipped and ENO is set to FALSE.

If the EN parameter is TRUE, the function body is executed. If the function executes without error, the ENO parameter is set to TRUE. If there is an error in the execution of the function, the ENO parameter is set to FALSE.

Informal Function Calls

In an informal function call, parameters are provided in the declared order. For example:

SEL( G, IN0, IN1 )

In an informal function call you cannot map variables to the implicitly declared EN and ENO parameters.

In an informal call, a runtime error in the function call will cause the program to halt.

Formal Function Calls

In a formal function call, parameters are declared by name. For example:

SEL( G:=expression, IN0:=expression, IN1:=expression )

In a formal function call you can map variables to the implicitly declared EN and ENO parameters. For example:

SEL( G:=expression, IN0:=expression, IN1:=expression, ENO=>Result )

The way IEC 61131-3 code handles errors in function calls changes depending on whether ENO is present or absent:

ENO Parameter	Effect of error
Absent	Causes the program to halt.
Present	The rest of the function is skipped. The ENO output is set to FALSE. Execution of the program continues.

Standard Functions

This table lists the common standard functions supported by Fernhill SCADA:

Function Type	Example
Conversion Functions	ANY_TO_STRING( 5 )
Mathematical Functions	SQRT( 5 )
Arithmetic Functions and Operators	ADD( A, 5 )
Bit Shift Functions	SHR( A, 4 )
Bitwise Boolean Functions	A AND 16#0F
Conversion Functions	QUALITY_TO_STRING( 192, TRUE )
Selection Functions	SEL( InputValue, 'Off', 'On' )
Comparison Functions	A > B
String Functions	FIND( 'The quick brown fox', 'quick' )
Date and time Functions	ADD_DT_TIME( DT#2013-01-07-16:46:00.000, T#4h30m)
Validation Functions	IS_VALID( %"Tag Reference" )
Type Information Functions	IsTypeOf( A, ANY_INT )

Extension Functions

This table lists the common functions supported by Fernhill SCADA:

Function Type	Example
System Functions	SysGetDateAndTime()
Operator Action Functions	OpenGraphic()

Further Information

IEC 61131-3 Common Elements

To learn about common elements of IEC 61131-3 scripts.

IEC 61131-3 Scripts

To learn about using scripts in Fernhill SCADA.

Glossary

For the meaning of terms used in Fernhill SCADA.