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The Wiegand interface is a wiring standard used for interconnecting peripherals like fingerprint readers, card swipers or iris recognition devices. Initially created by HID Corporation, the Wiegand devices gained popularity thanks to the popularity of the Wiegand effect card readers of the 1980s. The Wiegand interface is considered a de facto wiring standard for card swipe mechanisms, especially for electronic data entry.
The Wiegand interface consists of three wires in the physical layer, the first wire is for ground and other two for data transmission, known as Data low/DATA0 and Data high/DATA1. The wires are composed of an alloy with magnetic properties. DATA0 and DATA1 are pulled up to high voltage, when no data is sent. When "0" is transmitted, the DATA0 wire is pulled to a low voltage while the DATA1 stays at high voltage. When "1" is transmitted, DATA0 stays at high voltage, whereas the DATA1 is pulled to a low voltage.
The communication protocol used in the Wiegand interface is called the Wiegand protocol. The initial Wiegand format was comprised of only one parity bit, eight bits of facility code, and trailing parity bit of twenty-six bits. Although many access control systems did adopt Wiegand technology, the limitations of having only eight bits for site codes and eighteen bits for card numbers resulted in having the formats redesigned with different complexities to accommodate the different needs. Hence, in addition to the basic Wiegand format, different implementations to the basic Wiegand format which are inconsistent also became prevalent. However in its initial days, the Wiegand signalling format gave the unique benefit of providing very long cable runs compared to other prevalent standards for interface existing at the time.