Alias

A data type alias is the declaration of a user-defined data type that can be used to create an alternative name for a data type or a function block.

You declare an alias in a DUT object that you create using the command Add > DUT in the context menu of the PLC project tree in the project.

Syntax:

TYPE <DUT name> : <type name>;
END_TYPE

Permitted types

Sample:

PLC variable of type T_Message is always a string with 50 characters.

TYPE T_Message : STRING[50];
END_TYPE

Declaration:

sMessageA : T_Message;

Program:

sMessageA := 'This is a message';

Sample:

Alias data type for variables of type STRING or ARRAY if they require a specific length.

Declaration

TYPE FRAME : ARRAY[0..1499] OF BYTE; END_TYPE

TYPE SYMBOL : STRING(512); END_TYPE

Call

PROGRAM MAIN
VAR
    aFrame  : FRAME;
    sSymbol : SYMBOL;
END_VAR

PLC variable of type T_Message is always a string with 50 characters

Sample:

Alias data type for variables that require a different start value than the one provided by the compiler.

TYPE INDEX : DINT := -1; END_TYPE

Sample:

Alias data type for variables of a specific type that are only to contain a specific subrange of values of the original type.

{attribute 'qualified_only'}
VAR_GLOBAL CONSTANT
    cMaxRune : DINT := DINT#16#0010FFFF;
END_VAR

TYPE RUNE : DINT(0..GVL.cMaxRune); END_TYPE

See also:

• Object DUT