When configuring a Simulink block, you usually use a graphical user interface (GUI).  In this post I’m going to investigate the basics of programming a dynamic GUI using the mask editor. The Saturation block features In <a href="https://blogs.mathworks.com/seth/2008/08/05/advanced-masking-concepts/">my last post, I introduced the example of a Saturation block that can use fixed limits set in the mask dialog or dynamic limits set via input signals. Here is an animation of the mask GUI that configures the block for these different modes. When the Upper and Lower Limit Sources are internal, the block has a single input port.  When the Upper/Lower Limit Source is set to external, the block grows additional ports to accept signals that provide those limits. Mask dialogs can associate actions with its components.  Most Simulink block GUIs have a standard row of buttons along the bottom. These four buttons provide a consistent interface for Simulink blocks, and when you use the mask editor, you get them free.

• OK – apply changes and dismiss the GUI
• Cancel – abandon changes made in the GUI and do not change the block
• Help – display documentation for the block
• Apply – apply changes made in the GUI

I added the other elements of the Saturation GUI through the parameters tab of the mask editor: Each parameter of the mask has a row in the Dialog Parameters table.  The Prompt (1) is the text displayed next to the widget that sets the value.  The Variable (2) is the name of the variable set in the mask workspace when the GUI is applied.  The Type (3) controls the widget used for the parameter.  You can choose edit, checkbox or popup.  I picked popup for the parameters Upper Limit Source and Lower Limit Source parameters.  I set the popups (4) to display internal or external. The Upper Limit and Lower Limit parameters use the edit type. Each of the parameters also has an Evaluate (5) and Tunable (6) setting.  I want uplim and lowlim to have the values that are entered into the dialog.  If a MATLAB expression (like 'sin(x)+1') is used to set the value of the Upper Limit, I want that to be evaluated.  I don’t want the variable to hold the string that was typed into the edit field.  Tunable means the value of the parameter can change during the simulation.  Upper and Lower Limits will be tunable through the dialog if internal limits are used.  The Limit Source parameters are not tunable because they change the configuration of the block. It is not possible to reconfigure the model structurally in mid simulation. Dialog Callbacks Dialog callbacks (7) are called when the parameter is changed in the mask.  Use dialog callback for error checking and controlling the visibility and enabled/disabled setting of other parameters in the mask dialog.  In the Saturation mask dialog, the Upper Limit Source and Lower Limit Source parameters fire a Dialog callback when you click on them.  This is the mechanism for enabling and disabling the Upper Limit and Lower Limit Edit fields in the GUI. Key Point: Just like a handle graphics GUI, the Dialog callbacks run in the MATLAB base workspace. Program the callback as if you are running it from the MATLAB command line. Here is the uplimsrc_cb called when the uplimsrc parameter changes:

% uplimsrc_cb Dialog Callback

function uplimsrc_cb(blk)

en = get_param(blk,'MaskEnables'<span style='font-size:12.0pt;font-family:"Courier New";color:black'>);

switch get_param(blk,'uplimsrc')

    case 'external'

        en{2} = 'off';

    case 'internal'

        en{2} = 'on';

    otherwise

        disp('Should never get here'<span style='font-size:12.0pt;font-family:"Courier New";color:black'>)

end

set_param(blk,'MaskEnables',en)

  When you click on the uplimsrc popup and change it, this callback fires.  The callback:

• Gets the MaskEnables, which is a cell array of on/off values, one for each parameter
• Assigns the second element (corresponding to uplim) to off if uplimsrc is external, on if uplimsrc is internal
• Sets the MaskEnables to use the updated on/off values

If the block uses an external limit source, the corresponding fixed limit is disabled. Mask Dialog Callback Confusion I have found callbacks that modify the block contents are a major source of problems. Key Point: The mask dialog callback is for modifying the mask dialog, not the system. The documentation on mask callbacks also discusses this subject.  If you need to modify the contents of your system, do that in the Mask Initialization, which runs when you click the Apply or OK button.  That will be the topic of my next post. Now it’s your turn Do you have dynamic masks? Leave a comment <a href="https://blogs.mathworks.com/seth/?p=26&#comment">here.