which micro controller you using to interface RFID… let us know where excatly you got struct……..
here are some links which might help you out going through RFID
What is rfid? how it works? basics of RFID…
how to interface RFID with 8051??
interacing of RFID with 8051 using interrupt concepts
A small project with RFID security system…
toll plaza system using RFID