Create Data-Driven Events

To create data-driven events in Stateflow charts, use the change operator. When you change values in a chart, the chart generates internal signals, called implicit events, that cause the chart to transition between states or execute actions. Use the change operator to create state actions and transitions that react to these implicit events. For more information, see Control Chart Behavior by Using Implicit Events.

You can use the change operator to:

  • Monitor sensor readings and trigger transitions when values cross thresholds.

  • Create state machines that respond to signal values without using explicit event broadcasting.

  • Synchronize parallel states based on shared data changes.

  • Implement debouncing logic for noisy input signals.

When you use the change operator in transition conditions, the transition occurs when the specified data changes value.

When you use the change operator in on actions, the action executes when the chart detects a change in the specified data value.

To reference data in other states, use dot notation with the change operator. When multiple states or data objects share names, using dot notation prevents ambiguity.

Monitor a System by Using the change Operator

This example models a temperature monitoring system that uses the change operator in the state transitions. The system monitors the temperature and activates cooling when the temperature goes above the threshold. The parallel states, MonitoringSystem and CoolingSystem, handle monitoring and cooling functions separately but communicate through the coolingStatus data.

Stateflow chart that uses the change operator for data-driven events.

The MonitoringSystem starts in the Normal state and sets alarmCount to zero. The CoolingSystem state begins in the Off state and sets coolingStatus zero.

As the temperature rises and reaches WARNING_TEMP, the MonitoringSystem state transitions from the Normalstate to the Warning state due to changes with the temperature variable. This transition executes the entry action for Warning, which sets coolingStatus to 1.

The CoolingSystem state detects this change in coolingStatus and transitions from the Offstate to the On state. Once in the On state, the CoolingSystem executes its during action and decreases temperature by 0.5°C in each execution cycle.

When the temperature drops below WARNING_TEMP, the MonitoringSystem transitions back to the Normal state, but the CoolingSystem state remains in the On state until the temperature reaches RECOVERY_TEMP.

If the temperature continues to rise and reaches ALARM_TEMP, the MonitoringSystem state transitions from Warning to Alarm, and increments the alarmCount. The chart maintains this synchronized behavior by using the change operator to coordinate the parallel states.

Limitations

To avoid unexpected behavior:

  • Do not use the change operator with output data.

  • Use the change operator only with scalar variables, matrices, or structures.

  • Make sure that all instances of the change operator reference unique and valid data names.

See Also

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