SELECTION SCREEN f4 help on vbeln and description will come automatically

hi i got on eissue with requirement

i have i nput parameters , i need to get description automatically

i want to provide f4 help for vbeln

SELECTION-SCREEN : BEGIN OF BLOCK b1 WITH FRAME TITLE text-001.

PARAMETERS : p_matnr LIKE mara-matnr OBLIGATORY ,

p_charg LIKE mchb-charg OBLIGATORY,

p_werks LIKE marc-werks OBLIGATORY,

p_vbeln LIKE lips-vbeln ,

p_maktx LIKE LIPS-ARKTX .

here i need to provide f4 help for p_vbeln

and i need get description material and populate description automatically on the screen(same screen)

AT SELECTION-SCREEN ON VALUE-REQUEST FOR p_vbeln.

SELECT * FROM lips INTO CORRESPONDING FIELDS OF TABLE p_it_values

WHERE werks = p_werks

AND matnr = p_matnr

AND charg = p_charg

and vbeln = p_vbeln.

CALL FUNCTION 'F4IF_INT_TABLE_VALUE_REQUEST'

EXPORTING

• ddic_structure = 'WA_IT_VALUES'

retfield = 'VBELN'

• PVALKEY = ' '

dynpprog = sy-repid

dynpnr = sy-dynnr

dynprofield = 'VBELN'

TABLES

value_tab = p_it_values

• FIELD_TAB =

• RETURN_TAB =

• DYNPFLD_MAPPING =

EXCEPTIONS

parameter_error = 1

no_values_found = 2

OTHERS = 3

.

IF sy-subrc <> 0.

• MESSAGE ID SY-MSGID TYPE SY-MSGTY NUMBER SY-MSGNO

• WITH SY-MSGV1 SY-MSGV2 SY-MSGV3 SY-MSGV .

ENDIF.

but it's not working for f4 help and autoamtically description will come on

pls help regading this

suma