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Unified Display Interface
Computer network protocol

Unified Display Interface (UDI) was a digital video interface specification released in 2006 which was based on Digital Visual Interface (DVI). It was intended to be a lower cost implementation while providing compatibility with existing High-Definition Multimedia Interface (HDMI) and DVI displays. Unlike HDMI, which is aimed at high-definition multimedia consumer electronics devices such as television monitors and DVD players, UDI was specifically targeted towards computer monitor and video card manufacturers and did not support the transfer of audio data. A contemporary rival standard, DisplayPort, gained significant industry support starting in 2007 and the UDI specification was abandoned shortly thereafter without having released any products.

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Development

On December 20, 2005, the UDI Special Interest Group (UDI SIG) was announced, along with a tentative specification called version 0.8.12 The group, which worked on refining the specification and promoting the interface, was led by Intel3 and included Apple Computer, Intel, LG, NVIDIA, Samsung, and Silicon Image Inc.4

The announcement of UDI lagged the DisplayPort standard by a few months, which had been unveiled by the Video Electronics Standards Association (VESA) in May 2005. DisplayPort was being developed by a rival consortium including ATI Technologies, Samsung, NVIDIA, Dell, Hewlett-Packard, and Molex.5 Fundamentally, DisplayPort transmits video in packets of data, while the preceding DVI and HDMI standards transmit raw video as a digital signal; UDI took an approach closer to DVI/HDMI.6 The UDI specification 1.0 was finalized and released in July 2006. The differences between UDI and HDMI were kept to a minimum since both specifications were designed for long-term compatibility.7 Again, UDI lagged DisplayPort by a few months, which had released its finalized version 1.0 specification in May 2006.8

The group changed its title in late 2006 from "special interest group" to "working group"9 and contemporary press coverage noted that "UDI is weak when it comes to industry support", accurately predicting the future DisplayPort/HDMI duopoly.10 In early 2007 Intel started supporting the rival DisplayPort standard; anonymous sources stated the licensing fees associated with HDMI and incorporation of HDCP into DisplayPort swayed Intel's support.1112 Other vendors started to use HDMI version 1.3,13 and both Intel and Samsung withdrew their support from UDI. There have been no announcements made about UDI since early 2007 and the UDI website became no longer operational after 2007,14 and it appears the UDI standard was abandoned before products were released.

Technical

There were two UDI implementations: "external profile" (for desktop computers and displays) and "embedded profile" (for the internal display of a laptop computer).15: §1.9 

Under the external profile, data was transmitted using three differential data pairs and one differential clock pair using the TMDS encoding scheme.16: §1.9.1  The external profile is considered an extension of HDMI and is backwards-compatible with HDMI Rev. 1.2 displays; however, UDI does not carry audio information as it is targeted towards high-resolution computer monitors instead.17: §1.10.1  As HDMI is itself an extension of DVI with HDCP, UDI external profile is compatible with these standards as well.18: §1.10.2, 1.10.3 

The embedded profile was slightly different, using either one or three differential pairs, each of which carried both data and clock information. The embedded profile uses an ANSI 8b/10b encoding scheme instead.19: §1.9.2, 3.3.1, 3.3.2 

UDI provided higher bandwidth than its predecessors (up to 16 Gbit/s in its first version, compared to 4.95 Gbit/s for HDMI 1.0)20 and incorporated a form of digital rights management known as HDCP.21

Connector

The external and embedded connector implementations were electrically compatible and physically similar, each with a single row of contacts, but they had different form factors and contact counts. The "embedded" implementation was only specified for the display panel interface and had a single row of 26 contacts, while the "external" implementation had a single row of 22 contacts inside a metal shield with a physically keyed rectangular cross-section, resembling the USB Type A connectors.22: §7.2.2, 7.3.2  The contacts were spaced on a pitch of 0.6 mm (0.024 in) (external)23: §7.2.2  and 1.0 mm (0.039 in) (embedded).24: §7.3.2 

Three of the contacts were reserved for future upgrade possibilities.25: §7.2.1, 7.3.1  Transmit and receive plugs and receptacles were different physically, similar to peripheral cables with USB-A and USB-B on each end, requiring the UDI cable to be plugged in one way only.26: §7.2.2, 7.3.2  Bidirectional communication worked at a much lower data rate than that available for the single direction video datastream.

UDI external connector pinout27: Table 7-1 
PinSignalDescription
1RSVDReserved; second mate
2RSVDReserved; second mate
3RSVDReserved; second mate
4GndUDI Data2 shield; second mate
5UDI Data2+UDI differential data pair 2: +; second mate
6UDI Data2-UDI differential data pair 2: -; second mate
7GndUDI Data1 shield; second mate
8UDI Data1+UDI differential data pair 1: +; second mate
9UDI Data1-UDI differential data pair 1: -; second mate
10GndUDI Data0 shield; second mate
11UDI Data0+UDI differential data pair 0: +; second mate
12UDI Data0-UDI differential data pair 0: -; second mate
13GndUDI Clk shield; second mate
14UDI Clk+UDI differential reference clock: +; second mate
15UDI Clk-UDI differential reference clock: -; second mate
16GndGround; discrete wire; second mate
17CEC28Consumer Electronics Control (optional); second mate
18UDI APwr29UDI auxiliary power; second mate
19UDI CtrlClkUDI control clock; second mate
20UDI CtrlDataUDI control data; second mate
21UDI EPwr30UDI power: +5V; third mate
22UDI HPDUDI hot-plug detect; third mate
—Connector shellfirst mate
UDI embedded connector pinout31: Table 7-7 
PinSignalDescription
1VDD UDLSupply voltage for data link circuitry
2VDD UDL
3VDD UDL
4VDD UDL
5VSSSupply return for control and data link power
6VSS
7VSS
8VSS
9UDI Data0+UDI lane 0 data; only used for ×3 lane width
10UDI Data0+
11GNDShield for UDI Data0
12UDI Data1+UDI lane 1 data; used for ×1 and ×3 lane widths
13UDI Data1-
14GNDShield for UDI Data1
15UDI Data2+UDI lane 2 data; only used for ×3 lane width
16UDI Data2-
17GNDShield for UDI Data2
18RSVDReserved
19RSVD
20RSVD
21(Test pin)
22GNDGround return
23UDI EPwrSupply voltage for control link signals
24UDI CtrlClkUDI control link clock
25UDI CtrlDataUDI control link data
26UDI HPDUDI link hot-plug detect
Notes

References

  1. "Proposed New Interface to Bring Next-Generation Connectivity to PC Monitors and CE Devices" (Press release). Silicon Image, Inc. December 20, 2005. Archived from the original on December 24, 2005. Retrieved September 7, 2021. https://web.archive.org/web/20051224043737/http://biz.yahoo.com/prnews/051220/sftu056.html ↩

  2. "Next-gen display standard emerges for PC, HDTVs". EETimes. December 20, 2005. Retrieved August 15, 2006.[dead link] http://eetuk.com/tech/news/showArticle.jhtml?articleID=175007227 ↩

  3. George Hayek. "Unified Display Interface (UDI) Technical Overview" (PDF). Intel. Archived from the original (PDF) on April 9, 2006. Retrieved September 7, 2021. https://web.archive.org/web/20060409220321/http://www.udisig.org/news_events/idf_s06_udisig.pdf ↩

  4. Wolfgang Gruener (December 20, 2005). "Industry group promotes UDI as successor of VGA graphical interface". TG Daily. Archived from the original on December 23, 2005. Retrieved September 7, 2021. https://web.archive.org/web/20051223153922/http://www.tgdaily.com/2005/12/20/udisig_formation/ ↩

  5. Smith, Tony (21 December 2005). "PC, CE firms to develop 'unified' display connector". The Register. Retrieved 2 February 2023. https://www.theregister.com/2005/12/21/unified_display_interface/ ↩

  6. Dipert, Brian (January 4, 2007). "Connecting systems to displays with DVI, HDMI, DisplayPort: What we got here is failure to communicate". EDN. Retrieved 3 February 2023. https://www.edn.com/connecting-systems-to-displays-with-dvi-hdmi-displayport-what-we-got-here-is-failure-to-communicate/ ↩

  7. Tuan Nguyen (July 3, 2006). "Unified Display Interface Nears Release". DailyTech. Archived from the original on July 13, 2006. Retrieved September 7, 2021. https://web.archive.org/web/20060713025905/http://www.dailytech.com/article.aspx?newsid=3098 ↩

  8. Smith, Tony (4 May 2006). "VESA completes DVI successor". The Register. Retrieved 2 February 2023. https://www.theregister.com/2006/05/04/vesa_completes_displayport/ ↩

  9. "Unified Display Interface Work Group". Official web site. Archived from the original on November 19, 2007. Retrieved September 7, 2021. https://web.archive.org/web/20071119024856/http://www.udiwg.org:80/home ↩

  10. Smith, Tony (28 May 2007). "Any port in a storm: the display tech battle". The Register. Retrieved 2 February 2023. What we have then is a re-run of the old USB vs Firewire debate: two standards [DisplayPort and HDMI] that do, give or take a plus point or two, the same job largely as well as each other. In each case, sufficiently large industry camps have formed around each to ensure neither will vanish, and vested intellectual property and licensing interests means there's little chance of the two coming together into a single standard. https://www.theregister.com/Print/2007/05/28/display_technologies/ ↩

  11. Dipert, Brian (January 4, 2007). "Connecting systems to displays with DVI, HDMI, DisplayPort: What we got here is failure to communicate". EDN. Retrieved 3 February 2023. https://www.edn.com/connecting-systems-to-displays-with-dvi-hdmi-displayport-what-we-got-here-is-failure-to-communicate/ ↩

  12. O'Donnell, Bob (September 5, 2007). "HDMI: The digital display link". EE Times. Retrieved 3 February 2023. https://www.eetimes.com/hdmi-the-digital-display-link/ ↩

  13. Tuan Nguyen (February 19, 2007). "The Future of HDMI". DailyTech. Archived from the original on June 10, 2007. Retrieved September 7, 2021. https://web.archive.org/web/20070610101554/http://www.dailytech.com/The+Future+of+HDMI/article6098.htm ↩

  14. "Unified Display Interface Work Group". Official web site. Archived from the original on November 19, 2007. Retrieved September 7, 2021. https://web.archive.org/web/20071119024856/http://www.udiwg.org:80/home ↩

  15. "Unified Display Interface Specification, Revision 1.0a Final" (PDF). Unified Display Interface Working Group. July 12, 2006. Archived from the original (PDF) on September 28, 2007. https://web.archive.org/web/20070928062555/http://www.udiwg.org:80/udi_spec/UDI_1_0.pdf ↩

  16. "Unified Display Interface Specification, Revision 1.0a Final" (PDF). Unified Display Interface Working Group. July 12, 2006. Archived from the original (PDF) on September 28, 2007. https://web.archive.org/web/20070928062555/http://www.udiwg.org:80/udi_spec/UDI_1_0.pdf ↩

  17. "Unified Display Interface Specification, Revision 1.0a Final" (PDF). Unified Display Interface Working Group. July 12, 2006. Archived from the original (PDF) on September 28, 2007. https://web.archive.org/web/20070928062555/http://www.udiwg.org:80/udi_spec/UDI_1_0.pdf ↩

  18. "Unified Display Interface Specification, Revision 1.0a Final" (PDF). Unified Display Interface Working Group. July 12, 2006. Archived from the original (PDF) on September 28, 2007. https://web.archive.org/web/20070928062555/http://www.udiwg.org:80/udi_spec/UDI_1_0.pdf ↩

  19. "Unified Display Interface Specification, Revision 1.0a Final" (PDF). Unified Display Interface Working Group. July 12, 2006. Archived from the original (PDF) on September 28, 2007. https://web.archive.org/web/20070928062555/http://www.udiwg.org:80/udi_spec/UDI_1_0.pdf ↩

  20. O'Donnell, Bob (September 5, 2007). "HDMI: The digital display link". EE Times. Retrieved 3 February 2023. https://www.eetimes.com/hdmi-the-digital-display-link/ ↩

  21. Tuan Nguyen (February 19, 2007). "The Future of HDMI". DailyTech. Archived from the original on June 10, 2007. Retrieved September 7, 2021. https://web.archive.org/web/20070610101554/http://www.dailytech.com/The+Future+of+HDMI/article6098.htm ↩

  22. "Unified Display Interface Specification, Revision 1.0a Final" (PDF). Unified Display Interface Working Group. July 12, 2006. Archived from the original (PDF) on September 28, 2007. https://web.archive.org/web/20070928062555/http://www.udiwg.org:80/udi_spec/UDI_1_0.pdf ↩

  23. "Unified Display Interface Specification, Revision 1.0a Final" (PDF). Unified Display Interface Working Group. July 12, 2006. Archived from the original (PDF) on September 28, 2007. https://web.archive.org/web/20070928062555/http://www.udiwg.org:80/udi_spec/UDI_1_0.pdf ↩

  24. "Unified Display Interface Specification, Revision 1.0a Final" (PDF). Unified Display Interface Working Group. July 12, 2006. Archived from the original (PDF) on September 28, 2007. https://web.archive.org/web/20070928062555/http://www.udiwg.org:80/udi_spec/UDI_1_0.pdf ↩

  25. "Unified Display Interface Specification, Revision 1.0a Final" (PDF). Unified Display Interface Working Group. July 12, 2006. Archived from the original (PDF) on September 28, 2007. https://web.archive.org/web/20070928062555/http://www.udiwg.org:80/udi_spec/UDI_1_0.pdf ↩

  26. "Unified Display Interface Specification, Revision 1.0a Final" (PDF). Unified Display Interface Working Group. July 12, 2006. Archived from the original (PDF) on September 28, 2007. https://web.archive.org/web/20070928062555/http://www.udiwg.org:80/udi_spec/UDI_1_0.pdf ↩

  27. "Unified Display Interface Specification, Revision 1.0a Final" (PDF). Unified Display Interface Working Group. July 12, 2006. Archived from the original (PDF) on September 28, 2007. https://web.archive.org/web/20070928062555/http://www.udiwg.org:80/udi_spec/UDI_1_0.pdf ↩

  28. Only applicable for UDI to HDMI ↩

  29. Required for both source and sink, for active adapters or repeaters ↩

  30. Only applicable for UDI to HDMI ↩

  31. "Unified Display Interface Specification, Revision 1.0a Final" (PDF). Unified Display Interface Working Group. July 12, 2006. Archived from the original (PDF) on September 28, 2007. https://web.archive.org/web/20070928062555/http://www.udiwg.org:80/udi_spec/UDI_1_0.pdf ↩