DDC (Display Data Channel)
Defined Standard by VESA
DDC ( Display Data Channel) is a defined Standard by VESA. While DDC is just the description of the interface, the true data that is exchanged between graphic adapter card and monitor is called EDID (Extended Display Information Data). This data exchange is for identification of the attached screens and to read their video specifications mainly. Optimum resolutions and maximum resolutions as well as Gamma values part of this protocol. If a monitor is directly attached to a graphic adapter card the only concern is to have a connection cable that supports DDC transmission ( VGA: pins 12 an 15 need to be connected).
An extender or a switch in between?
But what happens if there is an extender or a switch in between? A lot of them do not support DDC at all or only with certain limitations. This may cause PCs not to boot up at all or show no video. Sometimes only a standard resolution can be displayed with no chance to change it anymore. Black Box has a variety of ServSwitches and ServSwitch Extenders that do support DDC. For other trouble causing applications the Ghost emulators can be used. They read the true DDC information from a monitor and store it in their non-volatile memory. If then being connected directly to the graphic adapter card DDC problems will never appear.