Wiegand Technology: An Overview
When you say wiegand interface, do you really know what you are saying? Many people ask the question of whether or not Mercury Security readers support wiegand? This question cannot be directly answered until until the question is clarified. Wiegand compatibility has two distinct aspects: data signaling (electrical), and data format (numeric content). Both impart specific requirements for the card reader to be compatible.
Due to the wide use of the wiegand interface in the 1980's, most access control systems accept readers that utilize the wiegand interface, both at a signaling level and for card data formatting. Therefore, in order for a product to be compatible with the "wiegand interface", it must be compatible with both the signaling standard, as well as the data formatting standard.
Many controllers in use today support wiegand signaling. The wiegand signaling standard utilizes two data lines to carry card data to the controller. They are named data1 and data0. As the names impart, the data1 line carries the "1" bits of the data stream to the controller, and the data0 line carries the "0" bits. The picture below is a graphical representation of a wiegand data stream for the binary value "01101". Each dip in the line represents a change from 5V to 0V, thus communicating the bit.
This wiegand format consists of a parity bit, 8-bit facility code, 16-bit user ID, and parity bit, for a total of 26 (1+8+16+1=26) bits.
With this basic understanding of how to parse the information in the 26-bit wiegand format, you can apply a similar convention to decode the data in other wiegand formats. Once you know the distribution of the data fields, you can extract the facility code and user ID fields.
(c) 2001 Mercury Security Corp. Information subject to change without notice.