Using Simulink

About Masks

A mask is a custom user interface for a subsystem that hides the subsystem's contents, making it apper to the user as an atomic block with its own icon and parameter dialog box. The Simulink Mask Editor enables you to create a mask for any subsystem. Masking a subsystem allows you to

• Replace the parameter dialogs of a subsystem and its contents with a single parameter dialog with its own block description, parameter prompts, and help text
• Replace a subsystem's standard icon with a custom icon that depicts its purpose
• Prevent unintended modification of subsystems by hiding their contents behind a mask
• Create a custom block by encapsulating a block diagram that defines the block's behavior in a masked subsystem and then placing the masked subsystem in a library

Mask Features

Masks can include any of the following features.

Mask Icon

The mask icon replaces a subsystem's standard icon, i.e., it appears in a block diagram in place of the standard icon for a subsystem block. Simulink uses MATLAB code that you supply to draw the custom icon. You can use any MATLAB drawing command in the icon code. This gives you great flexibility in designing an icon for a masked subsystem.

Mask Parameters

Simulink allows you to define a set of user-settable parameters for a masked subsystem. Simulink stores the value of a parameter in the mask workspace (see Mask Workspace) as the value of a variable whose name you specify. These associated variables allow you to link mask parameters to specific parameters of blocks inside a masked subsystem (internal parameters) such that setting a mask parameter sets the associated block parameter (see Linking Mask Parameters to Block Parameters).

Mask Parameter Dialog Box

The mask parameter dialog box contains controls that enable a user to set the values of the masks parameters and hence the values of any internal parameters linked to the mask parameters.

The mask parameter dialog box replaces the subsystem's standard parameter dialog box, i.e., clicking on the masked subsystem's icon causes the mask dialog box to appear instead of the standard parameter dialog box for a Subsystem block. You can customize every feature of the mask dialog box, including which parameters appear on the dialog box, the order in which they appear, parameter prompts, the controls used to edit the parameters, and the parameter callbacks (code used to process parameter values entered by the user).

Mask Initialization Code

The initialization code is MATLAB code that you specify and that Simulink runs to initialize the masked subsystem at the start of a simulation run. You can use the initialization code to set the initial values of the masked subsystem's mask parameters.

Mask Workspace

Simulink associates a MATLAB workspace with each masked subsystem that you create. Simulink stores the current values of the subsystem's parameters in the workspace as well as any variables created by the block's initialization code and parameter callbacks. You can use model and mask workspace variables to initialize a masked subsystem and to set the values of blocks inside the masked subsystem, subject to the following rules.

• A block parameter expression can refer only to variables defined in the subsystem or nested subsystems that contain the block or in the model's workspace.
• A valid reference to a variable defined on more than one level in the model hierarchy resolves to the most local definition.

• For example, suppose that model M contains masked subsystem A, which contains masked subsystem B. Further suppose that B refers to a variable x that exists in both A's and M's workspaces. In this case, the reference resolves to the value in A's workspace.

• A masked subsystem's initialization code can refer only to variables in its local workspace.

Creating Masks

See Masking a Subsystem for an overview of the process of creating a masked subsystem. See Masked Subsystem Example for an example of the process.

Creating Masked Subsystems

Masked Subsystem Example