User`s guide

4 External Mode
4-18
This picture shows the External Mode Control Panel with the batch
download option activated:
External Mode Operation
When external mode is enabled, Simulink does not simulate the system
represented by the block diagram. Instead, it performs an
Update Diagram
and downloads current values of all parameters as soon as you start external
mode. After the initial download, Simulink remains in a waiting mode until
you change parameters in the block diagram or until it receives data from the
target.
The Download Mechanism
When you change a parameter in the block diagram, Simulink calls the
external interface MEX-file, passing new parameter values (along with other
information) as arguments. (MEX-files are subroutines that are dynamically
linked to Simulink.)
The external interface MEX-file contains code that implements one side of the
interprocess communication (IPC) channel. This channel connects the
Simulink process (where the MEX-file executes) to the process that is executing
the external program.
The MEX-file transfers the new parameter values via this channel to the
external program. The other side of the communication channel is
implemented within the external program. This side writes the new parameter
values into the program’s
SimStruct (the data structure containing all data
relating to the model code).
“Parameter changes
pending” appears here if
you have unsent parameter
value changes
.