Hi Vinay,
Hope i understand you requirement.
After giving your Input you are pressing Enter Key.
So in Module pool->Flow Logic.
Declare.
CHAIN.
Module Calculatet3.
ENDCHAIN.
Double click on Module Calculatet3 it will go ABAP Editor
Add your PBO Logic inside the Module Calculatet3.
OR
You created a Customized push button for Enter.
Then you should enter your logic At PAI
Regards,
Venkat.