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Represent Operating Modes by Using States

A state describes an operating mode of a reactive system. In a Stateflow® chart, states are used for sequential design to create state transition diagrams.

States can be active or inactive. The activity or inactivity of a state can change depending on events and conditions. The occurrence of an event drives the execution of the state transition diagram by making states become active or inactive. For more information, see States.

Create a State

You create states by drawing them in the editor for a particular chart (block). Follow these steps:

  1. Select the State tool:

  2. Move your pointer into the drawing area.

    In the drawing area, the pointer becomes state-shaped (rectangular with oval corners).

  3. Click in a particular location to create a state.

    The created state appears with a question mark (?) label in its upper left-hand corner.

  4. Click the question mark.

    A text cursor appears in place of the question mark.

  5. Enter a name for the state and click outside of the state when finished.

The label for a state specifies its required name and optional actions. See Label States for more detail.

Move and Resize States

To move a state, do the following:

  1. Click and drag the state.

  2. Release it in a new position.

To resize a state, do the following:

  1. Place your pointer over a corner of the state.

    When your pointer is over a corner, it appears as a double-ended arrow (PC only; pointer appearance varies with other platforms).

  2. Click and drag the state's corner to resize the state and release the left mouse button.

Create Substates and Superstates

A substate is a state that can be active only when another state, called its parent, is active. States that have substates are known as superstates. To create a substate, click the State tool and drag a new state into the state you want to be the superstate. A Stateflow chart creates the substate in the specified parent state. You can nest states in this way to any depth. To change the parentage of a substate, drag it from its current parent in the chart and drop it in its new parent.

Note

A parent state must be graphically large enough to accommodate all its substates. You might need to resize a parent state before dragging a new substate into it. You can bypass the need for a state of large graphical size by declaring a superstate to be a subchart. See Encapsulate Modal Logic by Using Subcharts for details.

Group States

When to Group a State

Group a state to move all graphical objects inside a state together. When you group a state, the chart treats the state and its contents as a single graphical unit. This behavior simplifies editing of a chart. For example, moving a grouped state moves all substates and functions inside that state.

How to Group a State

You can group a state by right-clicking it and then selecting Group & Subchart > Group in the context menu. The state appears shaded in gray to indicate that it is now grouped.

When to Ungroup a State

You must ungroup a state before performing these actions:

  • Selecting objects inside the state

  • Moving other graphical objects into the state

    If you try to move objects such as states and graphical functions into a grouped state, you see an invalid intersection error message. Also, the objects with an invalid intersection have a red border.

How to Ungroup a State

You can ungroup a state by right-clicking it and then clearing Group & Subchart > Group in the context menu. The background of the state no longer appears gray.

Specify Substate Decomposition

You specify whether a superstate contains parallel (AND) states or exclusive (OR) states by setting its decomposition. A state whose substates are all active when it is active has parallel (AND) decomposition. A state in which only one substate is active when it is active has exclusive (OR) decomposition. An empty state's decomposition is exclusive.

To alter a state's decomposition, select the state, right-click to display the state's Decomposition context menu, and select OR (Exclusive) or AND (Parallel) from the menu.

You can also specify the state decomposition of a chart. In this case, the Stateflow chart treats its top-level states as substates. The chart creates states with exclusive decomposition. To specify a chart's decomposition, deselect any selected objects, right-click to display the chart's Decomposition context menu, and select OR (Exclusive) or AND (Parallel) from the menu.

The appearance of the substates indicates the decomposition of their superstate. Exclusive substates have solid borders, parallel substates, dashed borders. A parallel substate also contains a number in its upper right corner. The number indicates the activation order of the substate relative to its sibling substates.

Specify Activation Order for Parallel States

You can specify activation order by using one of two methods: explicit or implicit ordering.

  • By default, when you create a new Stateflow chart, explicit ordering applies. In this case, you specify the activation order on a state-by-state basis.

  • You can also override explicit ordering by letting the chart order parallel states based on location. This mode is known as implicit ordering.

For more information, see Explicit Ordering of Parallel States and Implicit Ordering of Parallel States.

Note

The activation order of a parallel state appears in its upper right corner.

Change State Properties

Use the State dialog box to view and change the properties for a state. To access the State dialog box:

  1. Right-click the state and select Properties.

    The State properties dialog box appears. For descriptions of properties, see Properties You Can Set in the General Pane and Properties You Can Set in the Logging Pane.

  2. Modify property settings and then click one of these buttons:

    • Apply to save the changes and keep the State dialog box open

    • Cancel to return to the previous settings

    • OK to save the changes and close the dialog box

    • Help to display the documentation in an HTML browser window

Properties You Can Set in the General Pane

The General pane of the State properties dialog box appears as shown.

You can set these properties in the General pane.

Property

Description

Name

Stateflow chart name; read-only; click this hypertext link to bring the state to the foreground.

Execution order

Set the execution order of a parallel (AND) state. This property does not appear for exclusive (OR) states. See Execution Order for Parallel States.

Create data for monitoring

Select this option to create state activity data. See Monitor State Activity Through Active State Data.

Function Inline Option

Select one of these options to control the inlining of state functions in generated code:

  • Auto

    Inlines state functions based on an internal heuristic.

  • Inline

    Always inlines state functions in the parent function, as long as the function is not part of a recursion. See Inline State Functions in Generated Code (Simulink Coder)

  • Function

    Creates separate static functions for each state.

Label

The label for the state, which includes the name of the state and its associated actions. See Label States.

Properties You Can Set in the Logging Pane

The Logging pane of the State properties dialog box appears as shown.

You can set these properties in the Logging pane.

Property

Description

Log self activity

Saves the self activity value to the MATLAB® workspace during simulation.

Test point

Designates the state as a test point that can be monitored with a floating scope during model simulation. You can also log test point values into MATLAB workspace objects. See Monitor Test Points in Stateflow Charts.

Logging name

Specifies the name associated with the logged self activity. Simulink® software uses the signal name as its logging name by default. To specify a custom logging name, select Custom from the list box and enter the new name in the adjacent edit field.

Limit data points to last

Limits the self activity logged to the most recent samples.

Decimation

Limits self activity logged by skipping samples. For example, a decimation factor of 2 saves every other sample.

Properties You Can Set in the Documentation Pane

The Documentation pane of the State properties dialog box appears as shown.

You can set these properties in the Documentation pane.

Property

Description

Description

Textual description or comment.

Document link

Enter a URL address or a general MATLAB command. Examples are www.mathworks.com, mailto:email_address, and edit /spec/data/speed.txt.

Label States

The label for a state specifies its required name for the state and the optional actions executed when the state is entered, exited, or receives an event while it is active.

State labels have the following general format.

name/
entry:entry actions
during:during actions
exit:exit actions
bind:data and events
on event_or_message_name:on event_or_message_name actions

The italicized entries in this format have the following meanings:

Keyword

Entry

Description

Not applicable

name

A unique reference to the state with optional slash

entry or en

entry actions

Actions executed when a particular state is entered as the result of a transition taken to that state

during or du

during actions

Actions that are executed when a state receives an event while it is active with no valid transition away from the state

exit or ex

exit actions

Actions executed when a state is exited as the result of a transition taken away from the state

bind

data or events

Binds the specified data or events to this state. Bound data can be changed only by this state or its children, but can be read by other states. Bound events can be broadcast only by this state or its children.

on

event_or_message_name

and

on event_name actions

A specified event or message

and

Actions executed when a state is active and the specified event occurs or message is present.

For more information, see Synchronize Model Components by Broadcasting Events and Communicate with Stateflow Charts by Sending Messages.

Enter the Name

Initially, a state's label is empty. The Stateflow chart indicates this by displaying a ? in the state's label position (upper left corner). Begin labeling the state by entering a name for the state with the following steps:

  1. Click the state.

    The state turns to its highlight color and a question mark character appears in the upper left-hand corner of the state.

  2. Click the ? to edit the label.

    An editing cursor appears. You are now free to type a label.

    Enter the state's name in the first line of the state's label. Names are case sensitive. To avoid naming conflicts, do not assign the same name to sibling states. However, you can assign the same name to states that do not share the same parent.

    After labeling the state, click outside it. Otherwise, continue entering actions. To reedit the label, click the label text near the character position you want to edit.

Enter Actions

After entering the name of the state in the label, you can enter actions for any of the following action types:

  • Entry Actions — begin on a new line with the keyword entry or en, followed by a colon, followed by one or more action statements on one or more lines. To separate multiple actions on the same line, use a comma or a semicolon.

    You can begin entry actions on the same line as the state's name. In this case, begin the entry action with a forward slash (/) instead of the entry keyword.

  • Exit Actions — begin on a new line with the keyword exit or ex, followed by a colon, followed by one or more action statements on one or more lines. To separate multiple actions on the same line, use a comma or a semicolon.

  • During Actions — begin on a new line with the keyword during or du, followed by a colon, followed by one or more action statements on one or more lines. To separate multiple actions on the same line, use a comma or a semicolon.

  • Bind Actions — begin on a new line with the keyword bind followed by a colon, followed by one or more data or events on one or more lines. To separate multiple actions on the same line, use a comma or a semicolon.

  • On Actions — begin with the keyword on, followed by a space and the name of an event or message, followed by a colon, followed by one or more action statements on one or more lines, for example

    on ev1: exit();
    

    To separate multiple actions on the same line, use a comma or a semicolon. If you want different events to trigger different actions, enter multiple on blocks in the state label. Each block specifies the action for a specific event or message, for example:

    on ev1: action1(); on ev2: action2();
    

The execution of the actions you enter for a state is dependent only on their action type, and not the order in which you enter actions in the label. If you do not specify the action type explicitly for a statement, the chart treats that statement as an entry action.

Tip

You can also edit the label in the properties dialog box for the state. See Change State Properties.

See Also

Related Topics