call a routine in a dynamic action.

Hi Experts,

i want to write a routine in which i can give the error msg while saving the infotype 0002 incase the given condition is not fulfilled.

Can you tell me where i can write this routine and how to call it in a dynamic action.

i hav written other types of dynamic actions before but never called any routine before

Plz give me the detailed info regarding writing a routine.

regards

TS