Stateflow

History Junctions

History junctions record the previously active state of the state in which they are resident. See the following sections for information on history junctions:

• What Is a History Junction? -- Presents a defining description and example of a history junction.
• History Junctions and Inner Transitions -- Shows how an inner transition to a history junction can immediately exit and reenter a state as a special behavior.

What Is a History Junction?

A history junction is used to represent historical decision points in the Stateflow diagram. The decision points are based on historical data relative to state activity. Placing a history junction in a superstate indicates that historical state activity information is used to determine the next state to become active. The history junction applies only to the level of the hierarchy in which it appears.

Use of History Junctions Example

The following example uses a history junction:

Superstate Power_on has a history junction and contains two substates. If state Power_off is active and event switch_on occurs, the system could enter either Power_on.Low or Power_on.High. The first time superstate Power_on is entered, substate Power_on.Low is entered because it has a default transition. At some point afterward, if state Power_on.High is active and event switch_off occurs, superstate Power_on is exited and state Power_off becomes active. Then event switch_on occurs. Since Power_on.High was the last active state, it becomes active again. After the first time Power_on becomes active, the choice between entering Power_on.Low or Power_on.High is determined by the history junction.

See Default Transition and a History Junction Example for more information on the semantics of this notation.

Flow Diagram Notation with Connective Junctions

History Junctions and Inner Transitions