How to make display only a feild in the PAI event.

Dear Freinds

in Custom infotype i have two requiremenst as

frist requiremnt : > i have two radio buttons , if one radio button is selected a particular field should be made display only so i have tried as

if p9007-zradono eq l_c_x. ---radio button is being checked

loop at screen.

if screen-name = 'P9007-ZFREQNCY' .

screen-input = 0.

screen-output = 1.

modify screen.

endif.

endloop.

endif

The above code is not working ....can any one please correct me.

second requirement is when i create a record the currency field (USD) should be

display only.in my custom infotype........ so i have used the below code it is working

i was able to do in PBO

if psyst-iinit = yes and psyst-ioper = insert.

loop at screen.

if screen-name = 'P9007-ZCOST' .

screen-input = '0'.

screen-output = '1'.

modify screen.

endif.

endloop.

endif.

please can any one let me know why i cannot make display only the field after selecting the radio button

so i have written in PAI ........but my logic of first requiremnt is not working.

i have tried putting the same logic in Chain endchain.

still now working............. What i should do in the case of PAI.

Regards

shanti.