How to Use Stateflow for Control Logic in Simulink

Use Stateflow in Simulink to create state machines and flow charts that control system behavior. Define states, transitions, and actions visually to implement control logic that reacts to inputs and events.

Syntax

In Stateflow, control logic is built using states, transitions, and actions. Each state can have entry, during, and exit actions. Transitions define conditions to move between states.

• state StateName: Defines a state.
• entry: action;: Action when entering a state.
• during: action;: Action while in a state.
• exit: action;: Action when exiting a state.
• transition [condition]: Moves to another state when condition is true.

stateflow

chart ControlLogic {
    state Idle {
        entry: disp("Entering Idle");
        during: disp("Idle state running");
        exit: disp("Exiting Idle");
    }
    state Active {
        entry: disp("Entering Active");
        during: disp("Active state running");
        exit: disp("Exiting Active");
    }
    transition Idle -> Active [inputSignal == 1];
    transition Active -> Idle [inputSignal == 0];
}

Example

This example shows a simple control logic with two states: Idle and Active. The system switches to Active when inputSignal is 1 and returns to Idle when inputSignal is 0.

stateflow

chart SimpleControl {
    input int inputSignal;
    state Idle {
        entry: disp("Entering Idle state");
        during: disp("Waiting in Idle");
        exit: disp("Leaving Idle state");
    }
    state Active {
        entry: disp("Entering Active state");
        during: disp("Running Active state");
        exit: disp("Leaving Active state");
    }
    transition Idle -> Active [inputSignal == 1];
    transition Active -> Idle [inputSignal == 0];
}

Output

Entering Idle state
Waiting in Idle
Leaving Idle state
Entering Active state
Running Active state
Leaving Active state
Entering Idle state

Common Pitfalls

• Not defining clear transition conditions can cause the state machine to get stuck.
• Forgetting to initialize inputs or outputs leads to unexpected behavior.
• Using complex conditions inside transitions can make debugging hard.
• Not using entry and exit actions properly may cause missed operations.

Always test transitions with simple conditions first and add complexity gradually.

stateflow

chart FaultyControl {
    state Start {
        // Missing transition condition
    }
    state Stop {
    }
    transition Start -> Stop; // No condition, causes immediate transition
}

// Corrected version
chart FixedControl {
    input bool go;
    state Start {
    }
    state Stop {
    }
    transition Start -> Stop [go == true];
}

Quick Reference

Concept	Description
State	Defines a mode or condition of the system
Transition	Condition to move from one state to another
Entry Action	Code executed when entering a state
During Action	Code executed while in a state
Exit Action	Code executed when leaving a state
Input	External signals that affect transitions

Key Takeaways

Use Stateflow to visually design control logic with states and transitions.

Define clear transition conditions to avoid unexpected behavior.

Use entry, during, and exit actions to control what happens in each state.

Test your state machine with simple inputs before adding complexity.

Initialize inputs and outputs properly to ensure correct operation.