Conditionally Executed Subsystems (Using Simulink)

Using Simulink

Creating a Triggered Subsystem

You create a triggered subsystem by copying the Trigger block from the Signals & Systems library into a subsystem. Simulink adds a trigger symbol and a trigger control input port to the Subsystem block icon:

To select the trigger type, open the Trigger block dialog box and select one of the choices for the Trigger type parameter, as shown in the dialog box below:

rising forces a trigger whenever the trigger signal crosses zero in a positive direction.
falling forces a trigger whenever the trigger signal crosses zero in a negative direction.
either forces a trigger whenever the trigger signal crosses zero in either direction.

Simulink uses different symbols on the Trigger and Subsystem blocks to indicate rising and falling triggers (or either). This figure shows the trigger symbols on Subsystem blocks:

Outputs and States Between Trigger Events

Unlike enabled subsystems, triggered subsystems always hold their outputs at the last value between triggering events. Also, triggered subsystems cannot reset their states when triggered; states of any discrete blocks are held between trigger events.

Outputting the Trigger Control Signal

An option on the Trigger block dialog box lets you output the trigger control signal. To output the control signal, select the Show output port check box.

The Output data type field allows you to specify the data type of the output signal as auto, int8, or double. The auto option causes the data type of the output signal to be set to the data type (either int8 or double) of the port to which the signal is connected.

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