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X100: Learning the Monitors EDID


Unlike digital video interfaces, analogue interfaces like VGA do not detect when the monitor has been changed.  They typically only detect the monitor and read the EDID on boot.  Therefore, a reboot would be required to ensure that the host is reading the expected EDID.  There are of course exceptions, particularly on some laptops where they do detect the presence of an external monitor.

Out of the box, each CATX-Module has a built-in EDID that supports a default set of resolutions. When the host computer boots, it reads the EDID directly from the CATX-Module, which determines which resolutions are available on its operating system.

To update the CATX-Module with the actual monitors EDID, which may offer different resolutions, the monitor, X100, CATX-Module and host need to be switched on in a particular order to pass the EDID down the chain.  The following instructions assume that the cables are physically connected between each of the components.


  1. Power up Monitor           
  2. Powered on X100.
  3. The X100 will read the EDID from the Monitor.
  4. Power on the host computer.
  5. The host computer will, in turn, provide power to the CATX-Module, either via the PS/2 connection or USB depending on the model.
  6. The CATX-Module will read the EDID from the X100 and store it locally.
  7. The host computer will then read the EDID directly from the CATX-Module.

The gif animation below, demonstrates how the EDID is passed from the monitor to the host computer, as each component is turned on.

X100 EDIDTransfer


Some host computers will power the CATX-Module whilst in standby. Check the CATX-Modules link lights to make sure that they are off until the host computer is powered on.  If you do find that the CATX-Module link lights are on when the host is in standby, you will need to re-connect the CATX module from the host when performing step 4 above.  You may also need to reboot the host afterwards if the available resolutions for the monitor have not changed.


Page last modified on Thursday September 17, 2020 06:51:49 GMT-0000