Press Release
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Managing EDID Part 2:
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In the previous installment published May 14, 2008, we covered the basics of EDID and Hot Plug events as they relate to switching and distribution of DVI video.
A complete EDID management system provides a choice between dynamic or fixed EDID. This offers the flexibility to deal with the variety of issues that can arise in a complex distribution system.
Fixed EDID can be selected from a menu of previously stored or user created EDID. Dynamic EDID includes either a direct pass through mode from the display to the graphics card or a previously stored or user created EDID assigned to a specific output channel of the switcher.
Fixed vs. Emulation
With Fixed EDID, when a graphics card is connected to the input of switch, a user-selected EDID will be present at that input. The graphics card will not "see" any activity of the switch beyond the input and will continue to behave as if it were connected directly to a monitor with that specific EDID. An analogy is the high-tech heist movie where the thieves create a video loop of the empty hallway showing on the security guards' video monitors. Meanwhile, the invaders are escaping with the goods through that same hallway and the guards are none-the-wiser. This is also referred to as "spoofing."
RGB Spectrum refers to a specific user-selected EDID associated with an output as an Emulated EDID. An Emulated EDID presents a continuous EDID to the graphics card, even if the display is disconnected, while still maintaining a dynamic profile.
When a switch changes configuration and an input source is routed to a different output, the graphics card will receive the emulated EDID of that output. So while more dynamic than a Fixed EDID, the graphics card still never "sees" the real-time EDID of the monitor. This function is useful in cases where the EDID from the monitor is not available, perhaps due to lack of a DDC channel; or where a user wants to provide a specific resolution to the display without allowing it to negotiate with the graphics adapter. Some fiber optic transport systems do not have a bi-directional capability to bring the EDID back to the graphics adapter.
Although rare, there are some display devices that do not supply an EDID. For some graphics adapters this presents a dilemma...what pixel format to send the monitor? Either Fixed or Emulated EDID configurations would work for this situation.
These two choices serve different purposes, but can be used simultaneously along with Pass Through, as needed for different channels, in a properly equipped matrix switch.
Some switchers allow the user to capture the EDID, allowing subsequent export to a PC for analysis, storage or editing. If two different displays are incompatible with each other's EDID, a new EDID that is compatible with both can be created in a third party EDID editor application. This EDID can then be imported back into the switch and supplied to the graphics card.
Arbitration
There is still the question about what happens to the EDID of multiple displays connected to a common source. When a
single source is connected to multiple outputs and the displays have different resolutions, there are generally two methods
of arbitration available:
1) Use the resolution of the lowest numbered output of the group
2) Use the resolution of the lowest resolution display in the group.
This solution applies when a dynamic EDID is used. A fixed EDID will obviate the need for arbitration, as the graphics card will only see the EDID associated with the input of the switcher to which it's connected and not see the EDID of the display devices.
EDID Configuration Choices
When making choices for a channel's EDID configuration in a multi-source to multi-display set-up, consider the following:
In a switcher with a proper EDID management system, the user is provided with the necessary tools to optimize matching resolutions between graphics cards and displays, avoid the need for computer reboots after a Hot-Plug event and replace a device's EDID with one selected by the user.
RGB Spectrum® is a leading designer and manufacturer of videographic and multimedia hardware subsystems. Products include the View™ family of video windowing systems, the RGB/Videolink® line of scan converters, The Linx® DVI Matrix Switcher, the DGy™ digital recording system, and SuperWall™, ComputerWall® and MediaWall® multi-screen display controllers. RGB Spectrum is based in Alameda, California, and can be reached at 510-814-7000 and on the internet at http://www.rgb.com.