Passing values from transaction to Smartform

Hello Experts,

I have to develop a smartform. which will be attached to transaction VL02N thru NACE.

My query is how do I pass the values from transaction to my smartform.

if it was an report program I would have had selection screen and I would pass the values thru function module which is generated by the smartform.

Since I am attahing the smartform to the Tcode. Please help .

Regards,

Vinu...