7
Technical manual
7.1
DVI routing
VSDxx is build to route DVI video signals (and their implicit display info) from inputs to outputs. It approves
DVI1.0 standard, having the maximum transfer rate of 1.65GBit/s on every video data differential line. With
that, you can have video resolutions of up to 1920x1200 Pixels (at 60Hz repetition rate) on each of the in-
puts and outputs.
Transporting that high data rates over copper cables will lead to signal (and content) degradation, the mo-
re the longer the cables become and the higher the resolutions are. To compensate that “cable loss”, VSDxx
has adaptive cable equalizers on every input port. As the equalisation is adjusted permanentely and auto-
matically, no user interaction is required. Using this equalizers will extend the cable length at each input to
more than 35m at maximum DVI resolution, high quality cables assumed.
After the signal improvement the video signal of each input is routed to a dedicated, special crosspoint
routing chip. This chip is able to route the video signal to one or many of its outputs. When routing only to
one output, this will set up a point-to-point interconnection, if it routes one signal to many outputs, this
makes a point-to-multipoint connection (diversity function).
The routing chip is a non-blocking switch, i.e. existing routings do not block / prevent new routings of
other inputs or outputs. Only one major rule will apply: one output can only show maximum one input. If
you select a new input for an output, the existing routing will break before making the new connection.
If you add a new output to a already routed input (i.e. already leads to another output port, too), the exist-
ing routing will not show any interrupt or signal errors.
All output signals leaving the routing chip are buffered with line drivers before going the the port’s DVI
connector. This will allow maximum cable length with good signal integrity at each output.
7.2
EDID handling
The DVI standard defines, that every DVI video source has to be able to find out the video features of a DVI
compliant displaying device. The idea behind is, that the source will find out, what resolutions (in size and
timing) are supported by the display, and then only send out “supported” timings and signals, so that the
display will always show best possible content.
To find out the display’s information dataset, there has to be a so called “DDC” (display data channel),
which is implemented between source and sink of a DVI video system. Technically speaking, there is a I²C-
Interface between source and sink, and a protocoll specification, how the source can read and interpret
display’s information data. Many publications call this dataset “EDID”, an acronym for “extended display
information data”. This manual will follow this definition.
As mentioned above, every displaying device has to provide EDID information when it is compliant to DVI
standard. As VSDxx acts as display device, seen from any video sources (like PCs), VSDxx must provide EDID
info compliant to DVI standards at any time. Even if VSDxx is de-energized, it has to provide that info! To
fullfill these requirements, a sophisticated EDID handling is built into VSDxx.
EDID handling is required for every input separately, so setup of EDID behaviour is available for each of the
inputs present separately. You can set up these modes of operation:
A)
EDID emulation („STATIC“):
The DVI input has a valid, static EDID information, that never changes automatically. The EDID
content can be a factory default or any EDID information that is read back from an attached
displaying device (which MUST provide an EDID). The static information on each DVI input port
is available for a video source even if VSDxx is de-energized; the video source provides a small
supply voltage through the DVI cable.
B)
EDID follow („FOLLOW“):
Having that mode, the DVI input holds a copy of the currently assigned output display’s EDID
info. If the input is routed to two or more outputs (point-to-multipoint configuration) , the
output with the lowest channel number will be the one used as source of EDID. If a change in
routing occurs (with respect to the input), the new EDID is copied to that input and the source
will receive a hotplug event to read the new EDID data.
If the input is unused (i.e. not routed to ANY output), then consequently there is no EDID avail-
able at that input, and the presence signal (hotplug) is removed for that input.
