Syntax for accessing variables

This chapter explains the syntax for accessing variables, field and structure elements and bits from integer variables.

This syntax is used both when specifying property values and at the programmatic level. The variable selection dialogue provides simple support when specifying property values. All linkable PLC values, i.e. the individual variables and the field and structure elements, are listed here for selection. Individual bits can also be selected from the selected identifier. The result is provided as a character string for transfer. So if, for example, you are writing a generator that compiles variable identifiers and problems arise with this at runtime, it is a good idea to select the variables addressed once in the variable selection dialogue and compare the character strings with your own result.

<Ch><VarAlias><element resolution>

with

<Ch>

The name of the channel ends with a dot (e.g. Ch1.). This part is omitted for internal variables.

<VarAlias>

The alias of the variable definition.

<element resolution>

Partially nested specification of field index, structure element name or bit number enclosed by curly brackets ({}).

The following rules apply to element resolution:

• A field element is specified using the 0-based index. The field element index is enclosed in square brackets ([]).
• A structure element is specified via the structure element name. The structure element name is identified by a leading dot and is not numerical.
• A bit number is specified via the 0-based bit index. The bit index is identified by a leading dot and is purely numerical.
• A bit range is specified via the 0-based bit indices of the start and end bit. The start bit is expected first, characterised by a leading dot, followed by the end bit, characterised by two leading dots.

Examples

The syntax examples shown below are interpreted from left to right:

MyInternalVar

Access to the internal variable MyInternalVar.

Ch1.MyVar

Variable MyVar in communication channel Ch1. See notes below.

Ch1.Simulation.MyVar

Variable Simulation.MyVar in communication channel Ch1.

Note: The variable name may contain dots that allow it to be divided into namespaces. The communication channel name must not contain a dot.

Ch1..Simulation.Variable1

Variable .Simulation.MyVar in communication channel Ch1.

By specifying a dot at the beginning of the variable alias, an empty namespace is created. This is used with some PLC types to designate global variables.

Ch1.Simulation.MyVar{.7}

Variable Simulation.MyVar in communication channel Ch1, access to bit 7.

Used for Boolean logic (e.g.: set a bit at the push of a button).

Ch1.Simulation.MyVar{.0..3}

Variable Simulation.MyVar in communication channel Ch1, access to bit group 0. .3 (4 bits).

Ch1.Simulation.MyVar{[2]}

Variable Simulation.MyVar defined as field in communication channel Ch1 (field size <> 0), access to field element 2.

Ch1.Simulation.MyVar{[2].7}

Variable Simulation.MyVar defined as a field in communication channel Ch1 (field size <> 0), access to field element 2, bit 7.

Used for Boolean logic (e.g.: set a bit at the push of a button).

Ch1.MyStructVar{.Var1}

Variable MyStructVar in communication channel Ch1, access to structure element Var1.

A structure is specified as the data type in MyStructVar.

Ch1.MyStructVar{.Var1.5}

Variable MyStructVar in communication channel Ch1, access to bit 5 in structure element Var1.

A structure is specified as the data type in MyStructVar.

Ch1.MyStructVar{.Var1[2].5}

Variable MyStructVar in communication channel Ch1, access to structure element Var1, here access to field element 2 and in turn access to bit 5.

A structure is specified as the data type in MyStructVar. A structure element can be a field or a structure itself.

Ch1.MyStructVar{.Var1.SubVar1}

Variable MyStructVar in communication channel Ch1, access to structure element Var1 and therein to structure element SubVar1.

A structure is specified as the data type in MyStructVar. A structure element can be a field or a structure itself.

Ch1.MyStructVar{.SS3[0].SubS2[10].15}

Variable MyStructVar in communication channel Ch1, access to structure element SS3 therein to field element 0, therein to structure element SubS2, therein to field element 10, therein to bit 15.

A structure is specified as the data type in MyStructVar. A structure element can be a field or a structure itself.

MyStructVar{.SS3[2].SubS2[22].0..8}

Variable MyStructVar in communication channel Ch1, access to structure element SS3 therein to field element 2, therein to structure element SubS2, therein to field element 22, therein to bit range 0..8 .

A structure is specified as the data type in MyStructVar. A structure element can be a field or a structure itself.