Sample ABAP Program to DIALOGUE FLOW LOGIC

PROCESS BEFORE OUTPUT.
MODULE STATUS_0100.
*
PROCESS AFTER INPUT.
MODULE EXIT_COMMAND AT EXIT-COMMAND.
* Data is not in the screen fields until after the field stateme
CHAIN.
FIELD:
S_TANUM,
S_TAPOS MODULE VAL_TANUM.
ENDCHAIN.
* chain ensures all fields are open after an error

CHAIN.
FIELD: S_ZZTRACKING,
S_EXIDV,
S_TANUM,
S_TAPOS MODULE VAL_ZZTRACKING.
ENDCHAIN.
* process data entered
MODULE USER_COMMAND_0100.