Variables

All variables used in programs must be declared first in the variable editor.

Each variable belongs to a group and must be identified by a unique name in its group.

Groups

A group is a set of variables.

A group refers to a physical class of variables or identifies the variables local to a program or user-defined function block.

This table lists the possible groups:

Groups	Description
%I...	Channels of an input board. Variables with same data type are linked to a physical input device. See Variables.
%Q...	Channels of an output board. Variables with same data type are linked to a physical output device. See Variables.
GLOBAL	Internal variables known by all programs.
PROGRAMxxx	All internal variables local to a program. The name of the group is the name of the program.
Retain Variables	Non volatile internal variables known by all programs. The latest values from RETAIN variables are stored from the Runtime into a file on the hard disk drive (HDD). In case of a warm (re)start, or a cold start, the Runtime initializes the variables with these stored values. The Runtime stores these values periodically per default, triggered every 10ms in an own, lower priority thread. The storage can be configured using either: The menu tab entry Project/Settings.../Runtime/Cycle time. The function F_SAVERETAIN used in the program code. If a device with zenon does not have a robust HDD, it is recommended to deactivate the periodical storage and store seldom. This can be done via a manual function call.
UDFBxxx	All internal variables local to a User-Defined Function Block plus its IN and OUT parameters. The name of the group is the name of the program.

Data Type and Dimension

Each variable must have a valid data type.

• It can be either a basic data type or a function block.
  • In a function block, the variable is an instance of the function block.
• Physical I/Os must have a basic data type.
• Instances of function blocks can refer either to a standard block or to a User Defined Function Block.

If the selected data type is STRING, you must specify a maximum length.
This cannot exceed 255 characters.

• See the list of Data Types.
• See Call a Function Block about using a function instance.
• Specify dimensions for an internal variable to declare Arrays.

Name a Variable

A variable must be identified by a unique name within its parent group.

• The variable name cannot:
  • be a reserved keyword of the programming languages.
  • have the same name as a standard or C function or function block.
  • See the List of C Functions webpage.
• A variable must not have the same name as a program or a user-defined function block.
• The name of a variable must begin by a letter or an underscore (_), followed by letters, digits, or underscore marks.
  • Two consecutive underscores in a variable name is not allowed.
• Naming is case-insensitive.
  • Two names with different cases are considered as the same.

Variable Attributes

Physical I/Os are marked as either Input or Output.

• Each internal variable can be configured as Read / Write or Read-only.
  • See Attributes.
    • Read-only variables can be mapped to Outputs but not to Inputs.
    • Inputs can change state and a Read-only variable cannot change its value to match the input state.
• Parameters of User-Defined Function Blocks are marked as either INor OUT.