Checking value in field
Hi sap gurus
My problem is
In T code JHA2n there is a screen field RJHA3001-Rabi_betr . this field is used to give discount.when user enters value into this field the value has to be checked in ztable and if value entered is wrong there should be an error message and he should be able to change the value in same field.
Can we check screen logic in exits. I mean can we give chain end chain statement in exits to check this.
Plese guide me how to use exits to accomplish this.