If you have looked at an HDMI, DisplayPort or DVI extender spec, you would have come across the term "EDID". So what is it and why is it important?
EDID (Extended Display Identification Data) is a standard that source devices (PC, game console, etc.) use to communicate with display monitors. EDID data is often stored in displays using a serial PROM (Programmable Read Only Memory) or a serial EEPROM (Electrically Erasable PROM). The display sends EDID to the source using the Display Data Channel (DDC), which is an I2C bus based mode. An I2C bus consists of three wires: SDA (serial data), SCL (serial clock), and a logic +5V line.
What is an EDID Handshake?
Any time a source is connected to a display, they have a conversation referred to as a "handshake". During this conversation, the display sends out important information about its capabilities — image size, color and timing characteristics. This conversation ensures that images show up correctly on the display.
Here is a sample EDID dump from a 4K monitor:
A sample EDID dump from a 4K monitor — the hex values encode the display's supported resolutions, refresh rates, color characteristics, and manufacturer identification that the source reads during the handshake.
Troubleshooting EDID Issues
Sometimes when the handshake does not happen correctly, issues arise. Displayed images may be non-optimal or may not show up at all on the display.
Most of these issues can be resolved by following the manufacturer's guidelines for correct EDID management. For example, in the case of LightBolt DVI extenders (VSA-100), the EDID programming procedure is as follows:
- Power on the display and plug the AC/DC power adapter into VSA-100-TR. Make sure the Power LED and EDID LED is on.
- Insert a small PIN into the EDID hole and push the EDID button continuously. When the EDID LED flashes rapidly, connect the VSA-100-Tx (transmitter) to the display. When the contents of the display's EDID are recorded, this LED will stop flashing and light continuously.
- Disconnect the AC/DC power adapter and remove the DVI module from the display.
Of course, if the factory settings work for you, manual programming is not required.
- Always connect the display to the source before switching the source on. Some sources only check EDID when starting up. When a new display is connected after boot, the source may transmit a default resolution which could result in skewed images.
- Sometimes adding adapters to your setup could strip the EDID data causing problems. Connect the source directly to the device to isolate the troublemaker.
- Keep cable lengths as short as possible. In the case of Active Optical Cables, the source provides power. If the cable is too long and the source does not provide enough power, the EDID conversation would stall and cause display issues.
