Hi
These links might help you:
1.https://www.engineersgarage.com/contribution/expert/rfid-based-attendance-system-using-8051-microcontroller
2.https://www.engineersgarage.com/microcontroller/8051projects/simple-toll-plaza-rfid-interface-at89c51-circuit
3.https://www.engineersgarage.com/microcontroller/8051projects/interface-rfid-AT89C51-circuit