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4. DDC and EDID
DDC
(Display Data Channel)
and monitor. The DDC is used to pass EDID
the monitor and describes its characteristics (vendor name, serial number, frequency range, etc.). With
this information the CPU and video card can determine what resolutions the monitor is capable of.
The DDC bus can be unidirectional or bidirectional. A bidirectional bus supports content protection
(HDCP) and display calibration software. (High-bandwidth Digital Content Protection is a specification
used to encrypt and protect digital video and audio signals transmitted between two HDCP-enabled
devices.)
NOTE: Most DVI-D graphics adapters will not boot if a valid EDID table is not received at
power up.
4.1. Default DDC Modes
4.1.1. Remote Dynamic Mode
System-3:
2 fibers required, System-6: 3 fibers required
The unit acts as a direct connection between the RX and TX. In this mode DDC data is read at the RX
and sent to the TX. Once verified at the TX the information is written into a PROM on the TX and
provided to the CPU video card. The RX will not send DDC data to the TX unless a different display is
connected to the RX.
Advantages:
Allows CPU video card to boot when there is no fiber connection to the RX.
Limitations:
No communication link from the CPU to the display. Prevents the use of HDCP or monitor
configuration /color tuning.
NOTE: When switching between DDC modes (except Pass-Thru), you will need to press the
ACQUIRE button to activate the new mode.
4.1.2 Remote Static Mode
Sys-3: 2 fibers required to acquire DDC data, 1 fiber thereafter
Sys-6: 3 fibers required to acquire DDC data, 2 fibers thereafter
Remote Static Mode is a subset of Dynamic Mode in that once a transfer from the RX to the TX is
completed successfully no other transfer will be made unless specifically requested by using the
ACQUIRE Button. The DDC data stored in the TX PROM will not change regardless of display changes.
Advantages:
Allows the user to acquire and use an EDID table regardless of changes in connection at
the RX.
Limitations:
No communication link from the CPU to the display. Prevents the use of HDCP or monitor
configuration/color tuning.
subsequently connected.
4.1.3 Pass-Thru Mode
Sys-3: 2 fibers required, Sys-6: 3 fibers required
The units act as a direct connection between the TX and RX. This mode allows the CPU to communicate
directly with the monitor.
Advantages:
Allows monitor color tuning and HDCP.
Limitations:
If a monitor is not connected to the RX most video cards will not boot.
4.1.4 Local Static Mode
Sys-3: 1 fiber required, Sys-6: 2 fibers required
V e l o c i t y D V I E x t e n d e r P r o d u c t M a n u a l , R e v . A , J u n e ,
is a VESA standard transport medium between a CPU's graphics adapter
(Extended Display Identification
May not produce video if a display with lower resolution capability is
Data), which is stored in
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