Interfacing Arduino Pro Mini with RFID and GSM

Hello
I have just started using arduino, so have a lot of doubts coming up.
I am interfacing pro mini with RFID ID-2 with external antenna...
I am using the Wire library.
I wanted to know how do I find out the
address of the RFID; the length ; the reset reader and checksum which is to be given in the code as follows :
eg:

Wire.beginTransmission(0x42); // the RFID reader's address is 42
Wire.send(0x01); // Length
Wire.send(0x80); // reset reader
Wire.send(0x81); // Checksum
Wire.endTransmission();
could you help me out.

I am interfacing pro mini with RFID ID-2 with external antenna...
I am using the Wire library.

Why? The reader is intended to be connected to a serial port. You can use NewSoftSerial and any pair of digital pins to read data from the device.

The checksum is output by the reader, based on the card presented. It is not an input value.