Why do I get an error when trying to feed enumerated data types through a 'Unit Delay' block?

In Simulink (R2021b), I have a signal that carries enumerated data into a 'Unit Delay' block. I then use the output of the 'Unit Delay' block elsewhere in my model. However, when I try to run my model, I get the following error:

'<my_model>/Unit Delay' cannot convert parameter InitialCondition from data type 'double' to data type '<MyEnumType>' because conversion of parameters with enumerated data types is not supported.

The documentation page for 'Unit Delay' says that enumerated data is supported, so what is causing this error and how can I resolve it?

Answer 1

[MathWorks Support Team]

Cause of the error:

This error is caused by the fact that the 'Initial Condition' parameter of the unit delay block is not of the same type as the inputted enumerated signal. When the model first runs, the value of the 'Initial Condition' parameter is passed through the model, so the 'Unit Delay' block expects data of the same type to be continuously fed into it. The next time step, when the enumerated data is fed in, the error is thrown since the data type of the input is different than the data type of the initial condition.

Resolution:

Change the initial condition of the 'Unit Delay' block to be an enumerated type value.

Examples:

Please see the model fails.slx for a demonstration of the issue, and the model works.slx for a solution to this issue.