When an atomic subsystem or function-call subsystem has event-based input signals, the subsystem has a restricted set of possible contents. The subsystem can contain:
Blocks having a Sample time parameter of -1, which indicates that the sample time is inherited from the driving block.
Blocks that always inherit a sample time from the driving block, such as the Bias block. To determine whether a block in one of the Simulink® libraries inherits its sample time from the driving block, see the "Characteristics" table near the end of the block online reference page.
Blocks whose outputs cannot change from their initial values during a simulation. For more information, see Constant Sample Time in the Simulink documentation.
The subsystem cannot contain:
Discrete-time blocks with a Sample time parameter value that is positive and finite.
In some cases, you can work around these restrictions by entering a Sample time parameter value of -1 or by finding a discrete-time analogue of a continuous-time block. For example, instead of using the continuous-time Clock block, use the discrete-time Digital Clock block with a Sample time parameter value of -1.