Creating Conditionally Executed Subsystems :: Creating a Model (Using Simulink)

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 the following 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 subsystem executes one or more times at the current time step when enabled by a control flow block that implements control logic similar to that expressed by programming language control flow statements (e.g., if-then, while, do, and for. See Modeling with Control Flow Blocks for more information.

Note Simulink displays an error if you connect a Constant, Model, or S-Function block with constant sample time (see Constant Sample Time) to the output port of a conditionally executed subsystem. To avoid the error, either change the sample time of the block to a nonconstant sample time or insert a Signal Conversion block between the block with constant sample time and the output port.

Controlling Access to Subsystems Enabled Subsystems