The importance of DDC in HDMI，do you know？
Most of us, when we start to use one piece of HDMI cable, we are facing a risk, that is compatibility issue! No matter what kind of HDMI cables –Passive Copper HDMI Cable, Active Copper HDMI Cable, or Active Optical Fiber HDMI cable, all of them have similar potential risk.
What is the compatibility?
Simply speaking, one cable, worked on one HDMI device, but do not work at another HDMI device, that is compatibility. Why this situation happened? That is today what we are talking about. First of all, we should start from some concept — DDC,EDID, I2C. Following is HDMI working principle .
DDC is short of Display Data Channel, it is a channel used for the Display/Screen/Monitors to tell the PC side Display/Screen/Monitors information (These information including: Resolution、Scanning Frame ),these spec. is key purpose is realized Plug & Play function. Enhanced DDC is defined by VESA ENHANCED DISPLAY DATA CHANNEL STANDARD Version 1 (September 2, 1999). According to HDMI definition, all Receiver side must support these enhanced DDC . Technically, from the Timing sequence, must be meet I2C standard, which means Data must be synchronize with SCL.Generally speaking, HDMI source side use I2C interface to read and receive E-EDID.
E-EDID is Enhanced Extended Display Identification Data Standard，defined by VESA。All Sink side，E-EDID must be follow VESA E-EDID Standard Release A, Revision 1，E-EDID total have128 bytes，it not only support EDID 1.3，but also support EIA/CEA-861B.
HDMI have total 19pin, at Pin 19, it is HPD ( Hot Plug Detective), this function is identify when Monitor/Screen/Display plug in or plug out with Source side(PC, STB,DVD), and Source side start to send EDID , and TMDS signal. All action is trigged by the HPD.
HDMI HPD, at HDMI Receiver Side (Sink), when E-EDID not ready for reading, signal can not be driven by High-Voltage. Also must be identified that Source side +5V power signal, then start to drive. HDMI device use this signal Voltage to trigger the E-EDID reading or not. Any change at the HDMI Sink side E-EDID, this signal drive is low-level voltage time should be 100ms, and low-level output voltage within 0.4V. Check following Circuit for your reference.
What is EDID ?
EDID, Extended Display Identification Data is a VESA standard data format that contains basic information about a monitor and its capabilities, including vendor information, maximum image size, color characteristics, factory pre-set timings, frequency range limits, and character strings for the monitor name and serial number.
From this article, we can simply learned that DDC is a road, and EDID is the information walking on this road. HPD is the trigger for Signal starting. When Sink and Source finished this communication system, we have a name “Hand Shake” success . This HDMI cable start its job — HDMI signal transmission, the TV screen is lighting.
HDMI AOC is short of HDMI Active Optical Cable, also belong to HDMI cable, have to follow the HDMI standard, have same requirements on the signal transmission system, and more complex than common passive copper HDMI cable. Smartavlink start HDMI AOC develop 7 years ago, we have a lot DDC/EDID/I2C application experience on design HDMI AOC, we are the first generation of HDMI AOC development team, in the past 7 years, we provide OEM/ODM service worldwide, we design and manufacturing following :
HDMI 2.0 AOC
HDMI 2.1 AOC
DP AOC
USB AOC
Type C AOC
Medical used special AOC
Industrial camera used special AOC
HDMI AOC engine
DP AOC engine
USB AOC engine
Also have converting series products, including:
DP to HDMI AOC
USB A to USB C AOC
USB A to USB B AOC
USB A to USB A female
HMDI to DVI AOC
DVI to HDMI AOC
If you want to learn more information about the HDMI AOC, DP AOC, and others, please contact info@smartavlink.com, or visit www.smartavlink.com