RFID Door lock

Hello, i bought a RFID door shield from Freetronics.com ( http://www.freetronics.com.au/products/dlock-rfid-door-lock-shield#.VNIcpCzqU9c ) and i bought also a compatible RFID reader from Priority1design.com.au ( http://www.priority1design.com.au/shopfront/index.php?main_page=product_info&cPath=1&products_id=37 ). I connected the reader to the door shield, and the door shield to my Arduino, but my RFID reader doesn’t read my RFID tag.

Now i was told by priority1design.com.au that the reader’s default is to read animal tag FDX-B or HDX. and if i’m using EM4100 (which i am) , i should send the command SD0 to the reader via the serial port. This set the default tag to EM4100.

My question is, how do i send this command? i’m completely stuck. HELP :’(

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