Good question. Model parameters are handled differently than model inputs and outputs. They are optimized for efficiently changing large numbers of parameters at the same time (in one clock cycle) without disrupting the execution of the model. Think of a PID controller as an example, where you need to update the P, I, and D parameters to tune the control algorithm, but you need to set them at exactly the same time so that they work with each other.
The channels in the system definition that represent the model parameters are read-only copies of the data. The model doesn't use these values for its calculations, so changing them would have no effect.
This is different than model inputs and outputs which are managed as channel values that are optimized to update continuously (every clock cycle).
The Stimulus Profile can change model parameters, because it runs on the host PC and uses a special function to change them in the background and apply those changes. A Real-Time Sequence runs in the control loop on the target. It doesn't have the same access to change model parameters in the background.
If there are variables you want to change dynamically in your model, you can consider using model inputs.
Jarrod S.
National Instruments
