Wiegand interface
{{Short description|De facto wiring standard}}
{{more citations needed|date=January 2021}}
The Wiegand interface is a de facto wiring standard which arose from the popularity of Wiegand effect card readers in the 1980s. It is commonly used to connect a card swipe mechanism to the rest of an access control system. The sensor in such a system is often a "Wiegand wire", based on the Wiegand effect, discovered by John R. Wiegand. A Wiegand-compatible reader is normally connected to a Wiegand-compatible security panel.
Physical layer
The Wiegand interface uses three wires, one of which is a common ground and two of which are data transmission wires usually called DATA0 and DATA1, alternatively labeled "D0" and "D1" or "Data Low" and "Data High".{{cite web
| title = Wiegand Interface
| date = June 2017
| publisher = Techopedia
| url = https://www.techopedia.com/definition/15326/wiegand-interface
| access-date = 2019-09-26
}} When no data is being sent, both DATA0 and DATA1 are pulled up to the "high" voltage level — usually +5 VDC. When a 0 is sent the DATA0 wire is pulled to a low voltage while the DATA1 wire stays at a high voltage. When a 1 is sent the DATA1 wire is pulled to a low voltage while DATA0 stays at a high voltage.{{cite web |title=Micro RWD EM4001 "Mag swipe" Decimal Output Version Data Sheet |url=https://eccel.co.uk/wp-content/downloads/magswipe_dec.pdf |publisher=ib technology |access-date=8 February 2021 |date=5 March 2005}}
The high signaling level of 5 VDC is used to accommodate long cable runs from card readers to the associated access control panel, typically located in a secure closet. Most card reader manufacturers publish a maximum cable run of {{convert|500|ft}}. An advantage of the Wiegand signalling format is that it allows very long cable runs, far longer than other interface standards of its day allowed.
Protocol
The communications protocol used on a Wiegand interface is known as the Wiegand protocol. The original Wiegand format had one parity bit, 8 bits of facility code, 16 bits of ID code, and a trailing parity bit for a total of 26 bits. The first parity bit is calculated from the first 12 bits of the code and the trailing parity bit from the last 12 bits.{{cite web |title=Understanding Card Data Formats - Technology Basics White Paper |url=https://www.idesco.com/files/articles/HID%20-%20Understanding%20card%20formats.pdf |publisher=HID Technology |access-date=14 February 2023 |date=2006}} However, many inconsistent implementations and extensions to the basic format exist.
Many access control system manufacturers adopted Wiegand technology, but were unhappy with the limitations of only 8 bits for site codes (0-255) and 16 bits for card numbers (0-65535), so they designed their own formats with varying complexity of field numbers and lengths and parity checking.{{cite web |title=What Is Wiegand? A Brief History |url=https://www.kerisys.com/2017/07/27/what-wiegand-brief-history/ |website=Keri Systems |date=27 July 2017 |access-date=8 February 2021}}
The physical size limitations of the card dictated that a maximum of 37 Wiegand wire filaments could be placed in a standard credit card, as dictated by CR80 or ISO/IEC 7810 standards, before misreads would affect reliability. Therefore, most Wiegand formats used in physical access control are less than 37 bits in length.
See also
References
{{reflist}}
External links
- [http://blog.opensecurityresearch.com/2012/12/hacking-wiegand-serial-protocol.html Open Security Research - Hacking the Wiegand Serial Protocol]
- [https://siamembers.siaonline.org/eweb/DynamicPage.aspx?Action=Add&ObjectKeyFrom=1A83491A-9853-4C87-86A4-F7D95601C2E2&WebCode=prDetail&DoNotSave=yes&ParentObject=CentralizedOrderEntry&ParentDataObject=Invoice%20Detail&ivd_prc_key=E08B09B6-BBB4-4EB1-A9E2-4BC7746267E0 SIA Standard, AC-01-1996.10 - Access Control - Wiegand]
- [https://www.youtube.com/watch?v=MHNJoHc_XDY LayerOne 2007 - Zac Franken - Wiegand Hacked (Video on Youtube)]
- [http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6988203.PN.&OS=PN/6988203&RS=PN/6988203 US Patent, System and Method of Extending Communications With the Wiegand Protocol]
- [http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=/netahtml/PTO/srchnum.html&r=1&f=G&l=50&s1=20070046424.PGNR.&OS=DN/20070046424 US Patent, Device Authentication Using a Unidirectional Protocol]
- [http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=/netahtml/PTO/srchnum.html&r=1&f=G&l=50&s1=%2220100034375%22.PGNR.&OS=DN/20100034375&RS=DN/20100034375 US Patent, Secure Wiegand Communications]