Table control in module pool program

Hi,

I have 2 screens 100 and 110 in my module pool program.

If I enter the hu_barcode value in the screen 100 and click enter control goes to screen 110 and appends the barcode value in the table control.Again if I enter a separate hu_barcode value in screen 110 and click enter that value also gets appended in table control of the same screen 110.

Now if I enter the hu_barcode value in screen 110 which I have entered for the first time in screen 100 that should not get appended in the table control as the value is already there in the table control.

How can I capture the values entered in table control?

I have given the following code in my program.But it is not working.

IF hu_barcode <> lv_exidv.

        APPEND wa_vekp TO tab_vekp.

      ENDIF.
      lv_exidv = wa_vekp-exidv.