Support For Ddc (Display Data Channel) - ADDER AdderLink AV100 series Manual

Support for DDC (Display Data Channel)

The Display Data Channel standard allows video monitors to define their
characteristics so that the source computers to which they are connected can
optimise their video outputs accordingly. By their nature, the AdderLink AV
extenders enable multiple video displays to be attached to a single source
computer. This causes a complication for handling the DDC standard, however,
in characteristic style we have devised an elegant solution, as detailed below.
Whenever an AdderLink AV transmitter is powered on, it checks its local video
port for a working display monitor with DDC information. The following strictly
ordered actions occur to automatically locate the most suitable DDC data:
• If a display monitor is discovered on the local video port of the transmitter,
the DDC data are cloned from it and stored within the transmitter.
• If no display monitor is discovered on the local video port of the transmitter,
the DDC data held within the transmitter will remain unchanged.
• If the DDC data or clock lines of the transmitter's local video port are
discovered to be connected to ground, then a default set of DDC data will
be reloaded and used.
After the initial search period, the stored DDC data are then presented to the
video port of the source computer. When transmitters are cascaded, only the
primary transmitter (the one connected to the source computer) will perform the
search for DDC data.
AdderLink AV transmitters hold two pages of DDC data in order to support the
most advanced display monitors. The DDC data are held within non-volatile
memory so that they are retained when power is removed.
The manner in which the transmitters search for suitable 'DDC donors'
could have an impact if your installation contains display units with differing
capabilities. Generally, you should arrange for the display monitor with the
most representative capabilities of your whole installation to be the one that
the transmitter locates on its local port, either initially (and temporarily) while
commissioning or permanently.
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