There are different options to create a new variable:

• Via a click on the Add variable context menu entry of the selected variable group. The variable is added at the end of the group.
• Via a click on the INSERT key, if a variable group is selected in the variable window. The variable is added at the end of the group.
  Hint: In both cases the variables are created with a default name. You can rename the new variable or change its attribute using the variable editing grid.
• Via the variable creation dialog. The dialog will be opened if you enter a new variable name for a variable, which does not exist.
  Example: Enter a name for a new variable in a function block input and click on OK. The variable creation dialog will be opened.

Variable creation dialog

The dialog allows to create a new variable and to define all relevant settings. The property Declare a new variable is preselected and cannot be changed.

The dialog view can be extended or collapsed.

Advanced

Navigation

You cannot insert a new variable in an I/O group.

In case of a group corresponding to local variables of a UDFB, pressing the INSERT key gives you the choice between:

• adding an IN (input) parameter.
• adding an OUT (output) parameter.
• adding a private variable.

IN and OUT parameters always appear at the beginning of a UDFB group.

Limitations

Specific variable types are stored in dedicated memory segments. Each segment is limited to 65534 variables. The error message at the end of compiling indicates an overflow (> 64534) in the segment:

XXX: Too many variables declared

where XXX indicates the segment. The following list shows the allocation of data types to the corresponding segments:

• FB: instances of C or standard function blocks
• BOOL/SINT: variables of type BOOL and 8 bits type: SINT, USINT and BYTE
• INT: 16 bits variables - type INT, UINT and WORD
• DINT/REAL: 32 bits variables - type DINT, UDINT, DWORD and REAL
• LINT/LREAL: 64 bits variables - type LINT, ULINT, LWORD and LREAL
• TIME: variables of type TIME
• STRING: variables of type STRING , regardless of the size of the STRING.

Each simple type variable counts for an item in the above mentioned segments. The segment-wise limits represent the total limit per project – regardless if the variable is declared for a POU (local), GLOBAL or RETAIN.

Hint: you can check the current quantities of variables and FB instances in all segments - in the configuration dialog of Online Change, when you (temporarily) enable it. This dialog is in menu Project - Settings... - General- Online Change: Enable; and after check you can disable it.

Limitations - Structures and Arrays

The effective limit for structures and arrays depends on the storage and handling of the related datapoints. These can either be managed in the basic segments (see limits above), or in a separate segment.

The related option is: Complex variables in separate segment

• Value = No:
  Structure- and array members are managed in basic memory segments. Limits are according to the above mentioned total number of variables per segment.
• Value = Yes:
  Structures and arrays are managed in a separate memory segment. The maximum number of variables in this segment is mainly limited by the available memory for this segment, as provided by the target Runtime Service. In any case, there is a total limit of approx. 4GB, based on 32-bit addressing in this segment.

In addition, there is a maximum array size of 10000000 elements.

Examples:

• 2 dimensions e.g. 256x255 = 65280 => OK
• 2 dimensions e.g. 256x100x1000 = 25600000 => ERROR

Created with the Personal Edition of HelpNDoc: Make Your PDFs More Secure with Encryption and Password Protection