ME21/22/23N (user exit) PBO

Hi Experts,

I have created a new tab with custom field for ME21/22/23N and I need to enable/disable parameter based on the tcode entered.

I found same problems in the internet and tried the solutions given but I cant figure out what I am missing.

I have entered my code in PBO and tried not to use validation first but still it does not disable the parameters.

Here is my code:

SAPMM06E      0111

PROCESS BEFORE OUTPUT.

* MODULE STATUS_0111.

MODULE modify_screen.

PROCESS AFTER INPUT.

* MODULE USER_COMMAND_0111.

MODULE MODIFY_SCREEN OUTPUT.

LOOP AT SCREEN.

     screen-input = '0'.

     MODIFY SCREEN.

ENDLOOP.

ENDMODULE.