EDID

showstack / protocols / edid

Also called Extended Display Identification Data, E-EDID, DDC.

The block of data a display hands to a source describing what it can accept — resolutions, refresh rates, colour depths, audio formats. The source picks a format from that list, which makes EDID the thing that decides what your screen is actually being sent.

Video controlOpen, free sign-upVESAReported

Not a traffic flow

A description a display hands over once at connection. Not a stream of anything.

What goes wrong

A splitter, switcher, extender or scaler usually presents its own EDID rather than passing the display's through. The source then picks a format the middle box likes and the screen may not.

Testing source-direct-to-screen removes every device that was doing the negotiating, so a working direct test proves less than it appears to.

Managed EDID is a setting. Deciding what it says is part of the design; discovering what it says at 5pm is not.

A distribution amplifier feeding several different displays has to pick one EDID to present. The lowest common capability is usually the right answer and rarely the default.

Typical use

Negotiating the format between any source and any display
Managed or emulated in switchers and scalers to force a known format
Read by test gear to diagnose why a source chose what it chose

Sources

VESA Enhanced EDID Standard — VESA primary

Understand the mechanism

Why the picture is black

Something wrong, or missing?

Known gaps on this entry: default_ports, first_published, implementations. If you can source one of them, that is a ten minute pull request.

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