Extended display identification data
Extended display identification data (EDID) is a data structure provided by a computer display to describe its capabilities to a graphics card. It is what enables a modern personal computer to know what kind of monitor is connected. EDID is defined by a standard published by the Video Electronics Standards Association (VESA). Version 3.0 of the standard (1997) defines a 256-byte structure, but there are older versions with only 128 bytes. The EDID includes manufacturer name, product type, phosphor or filter type, timings supported by the display, display size, luminance data and pixel mapping data (for digital displays only).
The channel for transmitting the EDID from the display to the graphics card is usually the I²C bus. The combination of EDID and I²C is called the display data channel version 2, or DDC2. The 2 distinguishes it from VESA's original DDC, which used a different serial format.
Before DDC and EDID were defined, there was no standard way for a graphics card to know what kind of display device it was connected to. Some VGA connectors in personal computers provided a basic form of identification by connecting one, two or three pins to ground, but this coding was not standardized.
The EDID is often stored in the monitor in a memory device called a serial PROM (programmable read-only memory) or EEPROM (electrically erasable PROM) that is compatible with the I²C bus.
|
