Custom fields on SAP standard screen - how to make them mandatory

Hi,

I have added 2 new custom fields [say zz1 and zz2] in the SAP Document Management System whilst creating documents in program SAPLCV110.

I want to have these fields set to mandatory only when the document type is say ZZZ.

Can you please let me know where abouts I need to go to introduce the code.

Regards,

Satish