What's a Parameter?

IEC 61499-1 uses the ISO 2382 definition of parameter as "A variable that is given a constant value for a specified application and that may denote the application." In the IEC 61499 world, the only variables that can be treated this way are input variables of function blocks, devices and resources.

Editing Parameters

You can set the value of a parameter from the popup menu of an unconnected input variable of a function block, device or resource. This menu will show a Connect item with sub-items corresponding to other variables that can be connected to it, as well as a default value for the variable if it is to be treated as a parameter.

• The value for a parameter of BOOL type can be chosen from the two possible values 1 and 0 .
• The value for a parameter of WSTRING type does not need to have leading and trailing double quotes (") unless:
  • The unquoted string would conflict with a possible connection source, e.g., an input variable name; or
  • it is the empty string (""); or
  • it has significant leading or trailing blanks (these are trimmed off of unquoted strings before saving the parameter).

Once an initial parameter value has been set, you can edit the parameter value by double-clicking on the parameter value or using the Edit item of its pop-up menu. This will open a dialog box with a text field for entering the modified parameter value. You can set the new parameter value by pressing the OK button or using the Enter key while typing. If the format of the entered data is incorrect, the data will not be entered and an INVALID_OBJECT error message will be displayed in the status line under the dialog box's title.

Viewing Parameters

IEC 61499-1, as published in January 2005, adopts the IEC 61131-3 style for representation of parameters as a list of name/value pairs associated with the declaration of an instance of an element instead of "constant" connections in a connection list. The FBDK now supports this style of representation in the src text view.

Saving Parameters

IEC 61499-2,as published in January 2005, also defines the representation of parameter lists rather than "constant connections" in its XML DTD. The FBDK now supports this style of representation in the XML text view and the File Save as XML format.

Hiding Parameters

Some variables can be identified a priori as being parameters, namely:

• Parameters of network segments and links
• The input variables of resources and devices
• Those input variables of function blocks which are associated with no event inputs, or only the INIT input, in the function block type declaration.

This information can be used by software tools to suppress the display of parameters as an option to remove clutter from the display of function block networks. In the FBDK Worksheet, parameter hiding is controlled from a Parameters checkbox item in a popup menu.