Regarding purchase order creation using me21n

Hi,

I want to set default values for Purch. Org for a document type PO:Service-FREIGHT in me21n transsaction.

which userexit or badi can be used for this?

When a document type PO:Service-FREIGHT is entered, Purch. Org should have deafualt value set automatically..

Through 'Personal Settings' it is possible but it applies for all document type..& I need it for dot tytpe

PO:Service-FREIGHT .

Thanks in advance...