Hi,
1. Please use google search, you may get useful information.
2.Have you used breakpoint statement in your filter routine code? if yes then you may get other wise its take more time to see your code.
use break point statement in your logic and debug your dtp.
I think you know how to debug dtp.
at dtp, execute tab, processing mode - Serially in the Dialog Process (for Debugging) and excute your dtp.
Thanks