Screen fields of Standard Transaction

Hello All,

I need to get all the screen fields of standard transaction..

For example we have ME21N (Create Purchase Order), I need all the screen fields which are given by SAP in this transaction.

Basically I need to generate a report which will download all the fields/Datatypes/Fieldnames in to a file...

Can some one let me know is there any function module for the same...

Regards,

Kumar