Real-Time Workshop

Limitations of External Mode

In general, you cannot change a parameter if doing so results in a change in the structure of the model. For example, you cannot change:

• The number of states, inputs, or outputs of any block
• The sample time or the number of sample times
• The integration algorithm for continuous systems
• The name of the model or of any block
• The parameters to the Fcn block

If you cause any of these changes to the block diagram, then you must rebuild the program with newly generated code.

However, parameters in transfer function and state space representation blocks can be changed in specific ways:

• The parameters (numerator and denominator polynomials) for the Transfer Fcn (continuous and discrete) and Discrete Filter blocks can be changed (as long as the number of states does not change).
• Zero entries in the State Space and Zero Pole (both continuous and discrete) blocks in the user-specified or computed parameters (i.e., the A, B, C, and D matrices obtained by a zero-pole to state-space transformation) cannot be changed once external simulation is started.
• In the State Space blocks, if you specify the matrices in the controllable canonical realization, then all changes to the A, B, C, D matrices that preserve this realization and the dimensions of the matrices are allowed.

Note    Opening a dialog box for a source block causes Simulink to pause. While Simulink is paused, you can edit the parameter values. You must close the dialog box to have the changes take effect and allow Simulink to continue.

Error Conditions

If the Simulink block diagram does not match the external program, Simulink displays an error box informing you that the checksums do not match (i.e., the model has changed since you generated code). This means you must rebuild the program from the new block diagram (or reload the correct one) in order to use external mode.

If the external program is not running, Simulink displays an error informing you that it cannot connect to the external program.

Running the External Program

Program Architecture