EDID Management – Installment 028

This Installment dives into the Extended Display Identification Data (EDID) data structure, which is the way that a display device “describes” its capabilities to the source.  EDID is defined by a standard published by the Video Electronics Standards Association (VESA).  It is what allows the source to know what the sink is capable of doing.  EDID structures have been around for quite some time and also are a key component of how VGA-based displays have been identifying themselves to computers for the couple of decades (since about 1994).  Note, also, that there also is the E-EDID (Enhanced EDID) structure, which supports multiple extension blocks and additional data fields, which is actually is used more in the HDMI world than the original EDID structure because of the additional information that can be conveyed.



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If you recall some of our earlier Installments on HDMI (http://thedigitallifestyle.com/cs/blogs/custom/archive/2009/11/04/The-Custom-Integrator-Show-Installment-020.aspx), the exchange of EDID information is a key component to the initial handshaking process for HDMI.  It is the first thing that is exchanged after the Hot Plug Detect is inserted.  Think of it as 128 Bytes of data with each Byte and its position in the data structure providing specific information about the display.  The source interprets that information and uses it as the means to send the highest possible quality video and audio signal that both devices can support.

There is a lot more to it than that, and we do not delve too deeply into the specifics of the data itself in this installment.  However, if you refer to the Pre-Cursor to Installment 028 on the blog site (http://thedigitallifestyle.com/cs/blogs/custom/archive/2010/04/06/Pre_2D00_Cursor-to-Installment-028-_2D00_-EDID-Management.aspx), you can see actual interpretations of the EDID data.  I highly recommend you look that blog post over before listening to this Installment.  It is tough to explain verbally what can be shown a lot more easily in a few pictures.

The Pre-Cursor shows the basics of the EDID structure and how the bytes are interpreted.  With the capabilities of E-EDID, however, the data strings now can be up to 32 KBytes to handle the additional data.  Some of the EDID Extensions assigned by VESA include:

  • Timing Extension (00h)
  • Additional Timing Data Block (CEA EDID Timing Extension) (02h)
  • Video Timing Block Extension (VTB-EXT) (10h)
  • EDID 2.0 Extension (20h)
  • Display Information Extension (DI-EXT) (40h)
  • Localized String Extension (LS-EXT) (50h)
  • Microdisplay Interface Extension (MI-EXT) (60h)
  • Display Transfer Characteristics Data Block (DTCDB) (A7h, AFh, BFh)
  • Block Map (F0h)
  • Display Device Data Block (DDDB) (FFh)
  • Extension defined by monitor manufacturer (FFh).
  • Why is all of this important?  It is the root of how the interoperability between the source and sinks work, although it is a lot more complex than we get into here.  It all fits together because the CEA-861-D InfoFrames we discussed earlier correlate directly to the Vendor Specific Data Block (VSDB) extensions used by E-EDID.  It is not only how the display identifies its capabilities, but how the information concerning the capabilities to render lossless audio and 3-D playback is transmitted.

    For a single display, it is not overly critical that you understand the details because it all happens pretty much automagically.  However, it is an essential piece of the complex puzzle that comes into play when you start attaching multiple displays to something like an HDMI Matrix Switcher and you try to play content to several displays simultaneously – especially when each one may have different characteristics that it supports.  That is why some many of the modern HDMI Matrix Switchers now include EDID (and really E-EDID) management tools.  It also becomes the basis for key purchasing decisions when selecting HDMI Matrix Switchers and the associated components.

    Making all of this work correctly will require the next generation of Custom Integration Programmers – those that can manage the EDID data correctly.  Without having the correct data exposed to the source side of the chain, it will not know what capabilities the rendering devices have.  Additionally, troubleshooting issues become a huge quagmire if, once again, you do not understand what is being communicated on the wire.  That is why we have spent so much time on the details of EDID, CEA-861, and the 3D_Structures.  The interoperability of these components are extremely essential to a successful distributed audio and video infrastructure.

    Spend the time learning as much as you can about EDID management.  Without a good working base of knowledge, you will not be able to deliver reliable and trouble-free installations in the digital audio and video world.  I guess a cannot say it more succinctly than that.  It is the future.

    Next time we cover my experience at the Panasonic “Touch the Future” exhibit and what is meant by the elusive marketing term “Full 3-D.”  Thanks for listening.



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