dynamicaly setting SCREEN-INPUT field in TABLE CONTROL

hai guys,

in my table control i have REFNUM field and some other fields.

now my task is,

in every row,i have to enable the REFNUM field of table control for editing only if REFNUM is blank.

else i shud disable it.(when REFNUM is filled).

all other fields should be always disabled.

(right now,i am just able to either totaly enable the entire REFNUM coloumn or or totaly disable it for editing,irrespective of the values it is holding.)

shravan ramidi