Wiegand protocol

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Wiegand protocol is a name for a system of sending data from a sensor such as a card reader or proximity sensor. It is commonly used to connect a card swipe mechanism to the rest of an electronic entry system. The sensor in such a system is often a Wiegand wire based on the Wiegand effect discovered by John R. Wiegand.

The Wiegand protocol is apparently not formally defined in any one place.

The Wiegand protocol consists of three wires, one of which is a common ground, and two data transmission wires, usually called DATA0 and DATA1, but sometimes also labeled Data High and Data Low. When no data is being sent both DATA0 and DATA1 are at the high voltage. When a 0 is sent, the Data Low wire (also called DATA0) is at a low voltage while the Data High wire (also called DATA1) stays at the high voltage. When a 1 is sent, Data High is at the low voltage while Data Low stays at the high voltage.

The high and low voltage levels are usually the TTL (transistor-transistor logic) voltage levels.

A series of bits are sent, followed by a parity bit or bits. The number of bits sent at once varies according to the device, with 26 bits being common.

[edit] Reference

A Wiegand protocol reader and converter

A very simple description of the Wiegand protocol

Another description of the Wiegand protocol (timing diagram on page 5)