User`s guide

Introduction
4-3
External Mode
Simulink external mode is a mechanism that manages communication
between Simulink and stand-alone programs built with the Real-Time
Workshop. This mechanism allows you to use a Simulink block diagram as a
graphical front end to the corresponding program (i.e., the program built from
code generated for that block diagram).
In external mode, whenever you change parameters in the block diagram,
Simulink automatically downloads them to the executing program. This
feature lets you perform parameter tuning in your program without
recompiling.
External mode makes use of the client/server model of computing, where
Simulink is a client that sends a request to the server (the external program)
to install new parameter values.