Make fields active on radiobutton selection

Hello all,

I have two radiobuttons and two fields.When I select first radiobutton, field1 should be active and when I select second radiobutton field2 should be active.I am able to achieve this using at selection screen output event.But the problem is that when I select first radiobutton, field1 should be mandatory and if I switch to second radiobutton from the first one, field2 should be mandatory. When I switch from radiobutton 1 to radiobutton 2, the validation for the field2 is kicked off even before the field is avaiable for input.How to achieve this?

Thanks

Sandeep