What is the difference between OSDP and Wiegand?

Wiegand and OSDP are technologies used in access control systems- including the access method (card, fob, etc.), reader, and controller.

What is Wiegand?

Wiegand is a technology invented in the 1970s by John Wiegand that became an integral part of access control systems in the 1980s. While the term “Wiegand” actually refers to a variety of things (the Wiegand effect, the Wiegand wiring standard, and Wiegand protocol), this article will focus mainly on the Wiegand wiring standard which makes up how an access control reader communicates with a door controller.

When an access card of a Wiegand format (i.e. 26-bit, 37-bit, etc) is held near a compatible reader, the reader receives the information encoded on the card’s tiny integrated circuit. This is typically a facility code and a card serial number. This data on the card (a series of 1s and 0s) is permanently written onto the card and cannot be changed.

The reader then converts that series of 1s and 0s into electrical pulses per the Wiegand interface standard which is made up of 3 wires: a common ground, DATA0 (aka Data Low) and DATA1 (aka Data High). In order to send the 1s and 0s to the controller, the reader will drop the voltage on the respective DATA wire in rapid succession; 1s over DATA1 and 0s over DATA0. The controller detects these changes in voltage and reinterprets them as 1s and 0s in the firmware.

What is OSDP?

As described by the Security Industry Association (SIA), “Open Supervised Device Protocol (OSDP) is an access control communications standard developed by the [SIA] to improve interoperability among access control and security products.” While OSDP has been under development for some time, it was just published as an IEC standard in July of 2020.

In contrast to a Wiegand reader which is essentially a basic one-way communication device, an OSDP reader is a “smart” device that can both communicate to the controller and receive communication from the controller. Not only does the OSDP reader send card data to the controller, but the controller can also communicate with the reader to monitor the state of the OSDP reader and to detect if the reader wiring has been tampered with. Furthermore, OSDP version 2 is able to communicate with the controller securely using AES 128-bit encryption eliminating the possibility of an attacker “sniffing” card data while it is being sent to the controller.