Using Simulink

Creating Conditionally Executed Subsystems

A conditionally executed subsystem is a subsystem whose execution depends on the value of an input signal. The signal that controls whether a subsystem executes is called the control signal. The signal enters the Subsystem block at the control input.

Conditionally executed subsystems can be very useful when you are building complex models that contain components whose execution depends on other components.

Simulink supports three types of conditionally executed subsystems:

• An enabled subsystem executes while the control signal is positive. It starts execution at the time step where the control signal crosses zero (from the negative to the positive direction) and continues execution while the control signal remains positive. Enabled subsystems are described in more detail in Enabled Subsystems.
• A triggered subsystem executes once each time a trigger event occurs. A trigger event can occur on the rising or falling edge of a trigger signal, which can be continuous or discrete. Triggered subsystems are described in more detail in Triggered Subsystems.
• A triggered and enabled subsystem executes once on the time step when a trigger event occurs if the enable control signal has a positive value at that step. See Triggered and Enabled Subsystems for more information.
• A control flow statement executes C-like control flow logic under the supervision of a control flow block. In all cases, the blocks executed reside in a controlled subsystem. In the case of if-else and switch control flow, the control block resides outside the controlled subsystem and issues a control signal to an Action Port block residing inside the controlled subsystem. In the case of while, do-while, and for control flow, a block with iterative control resides inside the subsystem, which it controls without an apparent control signal. See Control Flow Blocks for more information.

Controlling Access to Subsystems

Enabled Subsystems