# OSDP and Wiegand

Wiegand and Open Supervised Device Protocol (OSDP) are technologies used in access control systems, including the access method (card, fob, and so on), reader, and controller.

## What is Wiegand?

Wiegand is a technology invented in the 1970s by [John Wiegand](https://en.wikipedia.org/wiki/John_R._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](https://en.wikipedia.org/wiki/Wiegand_effect), the [Wiegand wiring standard](https://en.wikipedia.org/wiki/Wiegand_interface#Physical_layer), and [Wiegand protocol](https://en.wikipedia.org/wiki/Wiegand_interface#Protocol)), this article focuses on the Wiegand wiring standard. This standard explains how an access control reader communicates with a door controller.

### How it works

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#### When an access card of a Wiegand format (for example, 26-bit, 37-bit, and so on) 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**.

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#### The reader then converts that series of 1s and 0s into electrical pulses per the [Wiegand interface](https://en.wikipedia.org/wiki/Wiegand_interface#Physical_layer) standard, which is made up of 3 wires: a common ground, DATA0 (aka Data Low) and DATA1 (aka Data High).

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#### 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.

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#### The controller detects these changes in voltage and reinterprets them as 1s and 0s in the firmware.

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## What is OSDP?

[As described by the Security Industry Association (SIA)](https://www.securityindustry.org/industry-standards/open-supervised-device-protocol/), "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](https://www.iec.ch/dyn/www/f?p=103:38:4892262727330::::FSP_ORG_ID,FSP_APEX_PAGE,FSP_PROJECT_ID:1269,23,23397) in July of 2020.

### How it works

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#### 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.

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#### The OSDP reader sends card data to the controller and 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.

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#### 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.

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The Verkada AC41 currently only supports the Verkada readers when using OSDP.
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## What is the difference?

![](https://134288481-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FaaHs5RfKqv9Z49mi02cC%2Fuploads%2Fgit-blob-15e4237ff2066fe9f7c3f83c4b6361c5b97e0d0a%2F5a9d0cdcffdc55ee47d54900591a3bf5753fc951.png?alt=media)

## Verkada Support for Wiegand and OSDP

The Verkada access door controllers supports both Wiegand readers and the Verkada AD31. As shown, each door cassette on the AC41 has connection points for Verkada Readers using OSDP and Wiegand readers.

![](https://134288481-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FaaHs5RfKqv9Z49mi02cC%2Fuploads%2Fgit-blob-17801dcfee11e1a0340173756241b58a61858326%2F83feaa90fc1c37976180b0cbfbc06d521585fb7a.png?alt=media)

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**Need more help?** Contact [Verkada Support](https://app.gitbook.com/s/NRq5qDDjsYNxwNzF1bcB/need-help/contact-verkada-support).
