Hi,
Try like this,
In PBO,
loop at screen.
if screen-name = field_name.
screen-input = 0.
modify screen.
endif.
endloop.
For resetting the fields.
if sy-ucomm = 'RESET'.
if screen-name = field_name.
screen-input = 1.
modify screen.
endif.
endif.
Regards,
Riju Thomas.