BUS7:- This t-code used for Events in BDT.
create one Z function module and attach into corresponding events.Your Z fm will be triggered when the application calls.
Example DCHCK is the event for validation, create one Z fm and attach in this event it will be triggered and u can validate and show error messages.
You will not have any import and export parameteres for these FM.
U have to reterive the data from memory ( ex:- some BUT000GET function module)
Let me know if u need any more information on this!!!