User exit variable with ready to input process type

Hi,

I am trying to create a user exit variable that will calculate the previous period based on sysdate using standard funciton module DATE_TO_PERIOD_CONVERT. The variable should also work if user inputs a particular period it should only report on that particular period.

In other words, default to previous period with user input ready. I know the sap standard variable 0P_PRFP1 will give me previous period. If i make that variable user input enabled and user inputs period does it report on the user inputted period.

Is this possibule with one single varaible. Any other options?

Regards,

Reddy.