Wiegand Interface and Access Control Compatibility Guide

Are all Access Control card readers compatible with a Wiegand interface? How do I know if my access control system is compatible. This is not an easy question. The answer is driven by two aspects: (a) Data Signing, the electrical interface and (b) Data Format, the numeric content. To be compatible, both aspects (electrical and numeric content) need to impart specific requirements for the card reader. Before we answer the initial question (Are all Access Control readers compatible with a Wiegand interface), we first need to clarify the requirements to achieve compatibility.

The Wiegand interface is leading wiring standard which arose from the popularity of Wiegand effect card readers in the 1980s. The sensor in such a system is often a wire based on the electrical effect discovered by John R. Wiegand. The interface uses three wires, one of which is a common ground and two of which are data transmission wires usually called DATA0 and DATA1 but sometimes also labeled Data Low and Data High. When no data is being sent both DATA0 and DATA1 are at the high voltage (typically 5V). When a 0 is sent the Data Low wire (also called DATA0) is at a low voltage (typically 0V) while the Data High wire stays at a high voltage. When a 1 is sent Data High is at the low voltage while Data Low stays at the high voltage.

The data transmission method usually used by the Wiegand interface is a 26-bit data format. The picture below demonstrates a data stream for the binary value “01101″. Each change in the line or dip represents a change in electrical flow from 5V to 0V, thus communicating the bit.

A high voltage level of +5VDC is usually used to accommodate for long cable runs from the door readers to the controller. Most readers manufacturers publish a maximum of 500 feet.

The below figure demonstrates the use of a 26-bit data format. The 26-bit methodology is the most commonly used electrical data format. The data stream consists of a parity bit, 8-bit facility code, 16-bit user ID, and 1 parity bit for a total of 26 bits. [1 parity space + 8 facility code spaces + 16 user ID spaces + 1 parity space = 26 spaces (or bits)]

With a basic understanding of the 26-bit data format, a person can parse the methodology to decode the data stream for other less common formats. Once a person knows the distribution of the data fields, the facility code and user ID fields and by extracted.

Before you purchase an Access Control System visit the Wiegand Interface specialist at www.maglocks.com or call them toll free at (866) 500 – 5625

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