Wiegand Interface Definition - Honeywell Access · Wiegand Interface Definition ELECTRICAL...

Specifications subject to change

TECHNICTECHNICTECHNICTECHNICTECHNICAL BULLETINAL BULLETINAL BULLETINAL BULLETINAL BULLETIN

Northern Computers, Inc.5007 S. Howell Ave.Milwaukee, WI 53207USA

Tel: (414) 769-5980 • Toll-Free: (800) 323-4576Fax: (414) 769-5989

Northern Computers – UKModule C, Jenner RoadManor Royal Industrial ParkCrawley, SussexEngland RH10 2GA

Tel: +44 (0) 1293 552599Fax: +44 (0) 1293 523061

Northern Computers – EuropeThe Blue Tower326 Avenue Louise, 6th FloorB-1050 BrusselsBelgium

Tel: +32 2 645 1694Fax: +32 2 646 9934

Systémes Ordinés Northern1250, boul. René-Lévesque O.Bureau 2250Montréal, PQCanada H3B 4W8

Tel: 1-800-323-4576 / 514-989-3114Fax: 1-800-495-7050 / 514-989-3116

January 1996; Rev. 1.0

Wiegand Interface Definition

ELECTRICAL CHARACTERISTICS

Wiegand card readers contain a digital buffering circuit in which the signals generated in the read headby the Wiegand wires are separated into discrete digital “1” and “0” data pulses.

Typically the data is buffered and then output on two separate electrical signal lines with a commonsignal ground line. The data is transmitted at a fixed rate independent of the speed that the card waspulled through the reader. Both data lines are normally held high (typically +5vDC referenced to logiccommon), and are pulled low (typically TTL logic levels) for the duration of each output pulse. A data“0” is represented by lowering the Data-0 output line while the Data-1 output line remains high. A “1” isrepresented by lowering the Data-1 output line while the Data-0 output line remains high. A typicalpulse width is 50 microseconds with an inter-pulse spacing of 1 millisecond (refer to the diagram below).The actual timing values and tolerances and output circuitry are determined by the card reader manufac-turer.

The data packets are separated by a short dwell time (i.e. 500 milliseconds between cards).“Wiegand” proximity tag readers emulate the data stream of a card containing Wiegand wires.

DATA PROTOCOL

There are several different protocols used for transmitting serial data in a “Wiegand” format.

One common format consists of a 26 bit long serial stream consisting of 24 data bits and leading andtrailing parity bits. The leading bit in the stream is set to generate an even parity for the first 13 bitstransmitted while the trailing bit is set to result in an odd parity for the final 13 bits transmitted. The 24bits of data is then divided into an 8 bit “site code” followed by a 16 bit “user code” with the most signifi-cant bit for each code transmitted first. In the following diagram P represents the parity bits and Drepresents the data bits.

Other “Wiegand” formats send different numbers of data bits (ranging from 4 to 44) with different (orno) parity and with possibly some of the bits set high or low at fixed locations in the serial stream. Thedata itself can be partitioned in to any form imaginable.

TD2058

D ata-0 line

D ata-1 line1 m sec

50 µsec w ide+5v

0v

P

1

D

2

D

3

D

4

D

5

D

6

D

7

D

8

D

9

D

10

D

11

D

12

D

13

D

14

D

1 5

D

16

D

17

D

18

D

19

D

2 0

D

21

D

22

D

23

D

24

D

2 5

P

26

“Site Code”

B it set to 1 or 0 such that the total instancesof “1”s is an numbereven

B it set to 1 or 0 such that the total instancesof “1”s is an numberodd

“User Code”