Prior to an external mode run, you must specify the following for data to plot in a Simulink® Scope block:
Select Simulation > Mode > External.
Select one or more signals for capture (designated with "X") in the External Signal & Triggering dialog box from the External Mode Control Panel.
Set Duration * Fixed Step Size close to or less than the X range in the Scope block
Select required mode (one-shot or normal)
Configure signal levels to allow triggering
Set Y range on Simulink Scope block axes to large enough to span the signal amplitude
Set X range to large enough to provide required time resolution
Set Arm when connect to target in the External Signal & Triggering dialog box or Arm Trigger in the External Mode Control Panel.
Click the Run button on the toolbar.
If you cannot see signals plotted in your Simulink Scope blocks after carrying out these steps, your system might have too little CPU time available between sample intervals to transfer data back to MATLAB®, where the plotting is performed. To test for this condition, run one of the example models or run your model at a significantly slower sample rate.