The reader typically transmits a signal of 125 KHz.The smart card of the person is read by the RFID reader or wiegand reader near the door. The reader typically transmits a signal of 125 KHz. The card is a passive component with no power source. When it comes in proximity of the reader, the reader induces some voltage and hence the card transmits a unique 16 bit card number to the reader. The reader then transmits this card number to the microcontroller via the two data pins(D0,D1). Wiegand protocol is used for transmission. The 26 bit wiegand format is shown below.In the figure 3, the 1st bit is the even parity bit. This even parity is for the first 13 bits. This bit is followed by the 8 bit facility code(0-255). The facility code provides on more layer of security. This code is used in cases where the employees of 2 companies have the same card number. But they can be differentiated with the help of the facility code. The 8 bit facility code is followed by a 16 bit card number (0-65535). The last bit is the odd parity bit. The odd parity bit accounts for bits 14-26.