Specifications

RS-232 Synchronous Mode
2-9
4 In the Library window, double-click the RS-232 Synchronous mode group
block. The library window with blocks for RS-232 synchronous
communication opens.
Note This library contains two setup/receive blocks. The second block is
included for compatibility with xPC Target version 1.0.
5 Drag-and-drop an RS-232 Send/Receive block to your Simulink model.
6 Add a Signal Generator, and Constant block.
Your model should look similar to the figure shown below. Notice, the inputs
on the RS-232 Send/Receive block are not defined or visible. The inputs are
defined in a MATLAB message structure, and visible only after you load that
structure into the MATLAB workspace and update your Simulink model.