condition for scrolling in table control

Hi ,

I have a module in PAI inside loop of table control in which one field of table control is getting modified . But I don't want that to be triggered on scroll down .

I Check Sy-ucomm that is blank for scrolling and table control field

V_SCROLL is also blank.

What condition I should apply for that?

PROCESS AFTER INPUT.
LOOP AT it_tc.
CHAIN.
FIELD it_tc -field01.
FIELD it_tc-field02.
FIELD it_tc-field03.
FIELD it_tc-field04.
MODULE modify_data.
ENDCHAIN.
ENDLOOP.