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Detect falling edge in data since last time step in Stateflow chart

Since R2021b



tf = falling(expression) returns 1 (true) if:

  • The previous value of expression was positive and its current value is zero or negative.

  • The previous value of expression was zero and its current value is negative.

Otherwise, the operator returns 0 (false). If expression changes value from positive to zero to negative at three consecutive time steps, the operator detects a single edge when the value of expression becomes zero.

The argument expression:

  • Must be a scalar-valued expression

  • Can combine chart input data, constants, nontunable parameters, continuous-time local data, and state data from Simulink® based states

  • Can include addition, subtraction, and multiplication of scalar variables, elements of a matrix, fields in a structure, or any valid combination of structure fields and matrix elements

Index elements of a matrix by using numbers or expressions that evaluate to a constant integer.


Edge detection is supported only in Stateflow® charts in Simulink models.


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Transition out of state if the value of the input data signal falls below a threshold of 2.5.


Stateflow chart that uses the falling operator in a transition.

The falling edge is detected when the value of the expression signal-2.5 becomes zero or negative.


  • The operator falling imitates the behavior of a Trigger (Simulink) block with Trigger Type set to falling.

  • Edge detection for continuous-time local data and state data from Simulink based states is supported only in transition conditions.

  • In atomic subcharts, map all input data that you use in edge detection expressions to input data or nontunable parameters in the main chart. Mapping these input data to output data, local data, or tunable parameters can result in undefined behavior.

Version History

Introduced in R2021b