Interfacing EM-18 μRFID reader Wiegand26 with AT89S52

The communications protocol used on a Wiegand interface is known as the Wiegand protocol. The original Wiegand format had one parity bit, 8 bits of facility code, 16 bits of ID code, and a trailing parity bit for a total of 26 bits.

RFID is Radio Frequency Identification. An RFID reader is used to read RFID tags (which contain certain unique data stored in a chip). An RFID reader and an RFID tag, both have a coil surrounding them. When an RFID tag is shown near an RFID Reader, it collects the unique tag data (a combination of digits and characters) from the RFID tag. Power the μRFID reader; when an RFID tag is shown near the reader, electromagnetic induction will take place between the coils and this powers the chip inside tag. This chip will send data electromagnetically to the reader. The reader will receive this electromagnetically transferred data and output is in Wiegand format. We can collect the data by interfacing GPIO pins using AT89S52.

Wiegand26 communication can be enabled  by  giving low value to the SEL pin of the reader. The Wiegand interface uses two data transmission pins usually called DATA0 and DATA1, alternately labeled “D0″ and “D1″ or “Data Low” and “Data High”. When no data is being sent, both DATA0 and DATA1 are pulled up to the “high” voltage level usually, 3.3 – 5.5 VDC. When a 0 is sent the DATA0 wire is pulled to a low voltage while the DATA1 wire stays at a high voltage. When a 1 is sent the DATA1 wire is pulled to a low voltage while DATA0 stays at a high voltage.

The output in this mode is based on the table below-

Note:
E: Summed for even parity
O: Summed for odd parity
P: Parity(even or odd)
D: Data code for card

Interfacing μRFID reader Wiegand26 with AT89S52

A Wiegand format compatible output obtained by reading data pins connected directly to AT89S52. Make sure you connect Ground Pin of RFID reader to Ground Pin of AT89S52.

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Frequently Asked Questions(FAQ):

Q. What is the frequency range of μRFID reader?
Ans. The operating frequency range of RFID card is 125kHz.

Q. What are the protocols μRFID reader supported?
Ans. There are two supported protocols namely TTL Serial & Wiegand 26 as per the system design.

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