How to fix "? ? ?" display error in Simulink Model

I created a model with Z^-1 blocks, all blocks display in [z^-1] fine, however, after I built a subsystem with these blocks or copied them to another model, all Z^-1 blocks became ? ? ? instead of [z^-1]?

[Kaustubha Govind]

I'm assuming that you mean the "Integer Delay" block - what do you enter as "Number of delays"?

[Raymond Le]

the delay bock only -1 for each [Z^-1]

Answer 1

[Arnaud Miege]

The number of delays must be positive, you can't have a number of de lays equal to -1. Change it to a positive number. If I misunderstood your question and subsequent comment, please clarify what you mean.

HTH,

Arnaud