Asynchronous Signal Message
You define a Message as an asynchronous signal message by displaying the Message Properties dialog and setting the Synch field to Asynchronous and the Kind field to Signal. A synchronous message cannot be used to convey signals, so setting the Synch field to Synchronous disables the Kind field.
Return Value, Assign To and the Operations button, which are not applicable to asynchronous signals, are disabled.
The Operations button changes to a Signal button, which you click on to associate the asynchronous signal message with a Signal element in the model. You can type the arguments corresponding to the Signal attributes into the Argument(s) field.
When you click on the Signal button, the Select Signal dialog displays, through which you locate and select the required Signal element. (The Select Signal dialog is a variation of the Select <Item> dialog.)