Variables: Replacing and Editing
Further information on IEC 61131-3 variables is contained in the topic "IEC 61131 Implementation - Variables".
Replacing variables
You can replace the variables used in the code even if they are already associated to an LD object or connected to an FU/FB input or an output.
NOTE:
Safety-related and standard variables can be mixed in FBD/LD networks. In such mixed networks, leading safety-related signal paths are visually distinguished. Some rules and restrictions must be observed.
How to replace a variable by a new variable
With the following procedure, a new variable is inserted and declared at the same time.
Double-click on the variable to be replaced.
The 'Variable' dialog appears.
Select the 'Scope' of the variable:
To declare a new local variable, select the 'Local' radio button.
To declare a new global symbolic variable, select the 'Global' radio button.
Keep in mind that only global symbolic variables can be created this way but no global I/O variables. I/O variables are created automatically when dragging a process data item (device terminal) from the 'Devices' window and dropping it in a code worksheet. See topic "Declaration rules" for further information.
Enter a new variable name in the 'Name' field.
The remaining dialog fields are now activated and can be edited.
Naming conventions: EcoStruxure Machine Expert - Safety allows to use DIN qualifiers in IEC 61131 variable names.
Rules for using DIN qualifiers
According to the IEC 61131 standard, variable names can consist of letters, digits, and underscores. The identifier has to begin with a letter or an underscore. The use of any other character causes the compiler error "Illegal identifier".
This naming convention has been expanded in EcoStruxure Machine Expert - Safety in a way that IEC 61131 variable names may also contain DIN qualifiers:
The characters - + < > can be used at any position in the name and as last character. However, they cannot be used as first character of a variable name.
The DIN qualifiers / * # and the numbers 0 to 9 can be used at any position in the variable name.
Rules for using DIN qualifiers in IEC 61131 variable names
Variable names must at least contain one alphabetical character.
Variables must not have the name of an IEC 61131 data type, such as BOOL, INT, WORD, REAL, etc.
Variable names must not be defined as they are for literal values. Literals are used in the code by first specifying the literal data type, followed by a hash sign: <literal_prefix>#<value>. For example, SAFEINT#5 and WORD#32767 are literals. Therefore, a variable declaration such as safeint#MyVar would be invalid.
Literal prefixes are not case-sensitive and include the following keywords:
BOOL, REAL, LREAL, SINT, USINT, INT, UINT, DINT, UDINT, LINT, ULINT, BYTE, WORD, DWORD, LWORD, TIME, T, DATE, D, TIME_OF_DAY, TOD, DATE_AND_TIME, DT, STRING, TIMEDATE48, WEIGHT, ANALOG, UNIFRACT, BIFRACT200, FIXED, BOOLEAN2, BCD4, ENUM4, SAFEBOOL, SAFEBYTE, SAFEDWORD, SAFEINT, SAFEDINT, SAFETIME, SAFEWORD
In the dialog, specify the variable to be inserted by filling in the dialog fields.
In the combo box 'Data type' only data types can be selected that are allowed in the present context, i.e., the available entries depend on the selected formal parameter or object.
When declaring a global symbolic variable, no 'Usage' can be selected because the declaration keyword VAR_GLOBAL automatically applies to the global variables.
Finally press 'OK' to insert the variable into the code and the declaration into the corresponding variables worksheet.
How to replace a variable by a variable which is already declared
Double-click on the variable to be replaced.
The 'Variable' dialog appears.
Select the 'Scope', i.e., the variables worksheet where the declaration is contained by marking the corresponding radio button.
Select the 'Group' where the declaration is located in the variables worksheet (specified by the 'Scope').
Open the 'Name' combo box and select the variable to be inserted.
Click 'OK' to close the dialog and insert the variable.
Modifying properties of variables used in a code worksheet
In order to modify the declaration of a variable already used in a code worksheet, proceed as follows:
Right-click on the variable to be edited and select 'Go to definition of variable_name' from the context menu.
The variables worksheet is opened and the declaration line is marked.
Modify the variables properties by editing the columns in the variables worksheet.
Save the variables worksheet.
Verify the use of the modified variable in the code. Make certain that it is used correctly even if you have modified its data type or initial value.
NOTE:
Modifying the name of an already used variable means inserting a new variable. Verify the code carefully after such modifications.
