This article describes the difference between the X003 Invoke Exec Module
and the X004 Call Exec Module.
The X003 Invoke Exec Module command actually runs the external procedure.
You call this module after you have loaded the procedure and want it to
execute for the first time to initialize its structures and perform its
function.
The X004 Call Exec Module command passes data to an external procedure that
has already been run by the X003 command. The data is passed in the
"msgData" field of the TRMsg record that is sent to your external field.