Inside an HDMI cable
There are nineteen pins in an HDMI connector, as seen in the following illustration:
Pins 1 through 9 carry the three TMDS data channels (Transition Minimized Differential Signaling – the technology that allows DVI and HDMI to send high-speed digital data), three pins per channel. TMDS data includes both video and audio information, and each channel has three separate lines for + values, – values, and a ground or data shield.
Pins 10 through 12 carry data for the TMDS clock channel, which helps keep the signals in synchronization. As with the TMDS data channels, there are separate lines for + values, – values, and a data shield.
Pin 13 is carries the CEC (Consumer Electronics Control) channel, used for sending command and control data between connected devices.
Pin 14 is reserved for future use.
Pins 15 and 16 are dedicated to the DDC (Display Data Channel), used for communicating EDID (Extended Display Identification Channel) information between devices.
Pin 17 is a data shield for the CEC and DDC channels.
Pin 18 carries a low-voltage (+5V) power supply.
Pin 19 is the Hot Plug Detect, dedicated to monitoring power up/down and plug/unplug events.
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Running Long Cable Lengths
Like all HDMI-enabled components, cables must be tested to meet the Compliance Test Standards set by the HDMI Licensing, LLC. Cables must successfully pass a signal of a certain strength (Standard cable must deliver a signal of 17Mhz; High Speed must deliver a signal of 340Mhz) to pass compliance.
The HDMI specification does not dictate cable length requirements. Different cables can successfully send HDMI signals various distances, depending on the quality of the design and construction. As well, HDMI compliance testing assumes “worst case” scenarios – testing with components who have minimally performing HDMI electronics. That is why you may see cables in the market that claim to successfully pass an HDMI signal at very long lengths. This may be true using certain quality CE components on each end, but may not work in every case. It is best to test entire systems before installing.
Active Cables & Boosters
Using active electronics to boost and clean up the signal can effectively double the range of a standard twisted-copper HDMI cable. Cable runs of up to 30 meters are the norm for this type of solution, which may be deployed as either a standalone signal management device, i.e., a repeater or booster box, or incorporated into the manufacture of the cable itself. Boxes are available in many configurations, usually incorporating both booster and equalization functions, and may also serve as repeaters or switchers. Active cables, on the other hand, embed the signal-enhancement electronics in the cable itself, with chips embedded in the connector housings. They are unidirectional, using different modules at the transmit and receive ends of the cable. All the technologies in this category require external power.
Beware products that draw power from the +5V power line. Although these may work in certain applications, different components draw varying amount of power from that line to communicate with each other. A cable that draws power from the HDMI cable may fail when components and the active components in the cable or external booster are all drawing from the same source.
HDMI over Cat 5/6
Runs of up to 50 meters can be achieved by sending the HDMI signal over a run of Cat 5/6 networking cable, using special adapters designed for this purpose. As with the active cable solutions discussed above, they incorporate booster and equalization electronics at each end of the path, and require external power. Because of its tighter manufacturing tolerances, Cat 6 cable is generally preferred over Cat 5 in these applications.
HDMI over coax
This technique consists of a transmitter / receiver pair that convert HDMI signals for transmission over RGBHV or RGBS coaxial cables. The benefits of this solution are long reach (up to 300 feet at 1080p resolutions), the ability to easily terminate connections in the field, and an easy upgrade path for existing RGBHV or RGBS coaxial installations in office or commercial installations.
HDMI over Fiber
The longest HDMI cable runs seen to date have been achieved using fiber-optic cable, which is far less susceptible to attenuation and interference than copper. Electrically it is similar to an active cable or Cat 5/6 solution, the principal difference being the higher-quality optical cabling between the transmit and receive connectors. HDMI over fiber is a highly robust solution, effective in cable runs up to 100 meters or more.
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Connecting HDMI Devices
What you need to Know about HDMI Cables
The HDMI specification does not limit cables to any particular length, but instead sets performance criteria based on maintaining adequate signal strength. Therefore, cable length is not determined by the HDMI specification, but by the design and manufacturing quality of the cable.
Finding the Right Cable
With the release of the HDMI 1.4 specification, there are now five HDMI cable types to choose from, each designed to meet a particular performance standard. Here is an overview of the HDMI cable types, their capabilities, and how to tell them apart. (more)
For whole-house installations and other long-run configurations, there are many options available for extending the signal over greater distances (See Running Long Cable Lengths).
Sourcing HDMI cables
Manufacturing quality can make a big difference in a cable that can withstand the demands of a home installation, so it’s always a good idea to buy from a reliable, trusted source. Bargain cables are not always a bargain, especially when pulling through walls and sending signals over distance.
Pulling HDMI Cable
Remember how much data is running through that cable and treat it with a light touch. Tolerances are tight, so be careful – don’t yank HDMI cables or twist connectors. For in-wall installations, pull-through socks are available that will protect the connector as the cable is pulled through the wall or conduit. This is a particularly good idea if you are installing an active cable, where the connectors are larger and more sensitive because of their embedded electronics.
HDMI Connector Types
The HDMI specification defines three connector types, but only two are in common use. Most products rely on the Standard (Type A) connector, but many newer portable devices such as HD videocams and digital still cameras are incorporating the Mini Connector (Type C). Standard to Mini adapters are widely available.
Keeping Connectors Seated
You may occasionally experience difficulty keeping an HDMI connector seated. It could be a wall-mounted flat-panel with vertically-oriented connectors that want to fall out, or a projector with the connectors inside the outer case, or a badly designed overmolding that makes it difficult to get a flush fit. As well, overly heavy cables can put undue strain on the connector.
The HDMI licensing authority is actively evaluating solutions for a locking connector, but in the meantime, fixes are available. There are swivel adapters that fit between the port and the cable, allowing you to adjust the angle of the connection as needed in both the “x” and “y” directions, and fix it in that position.
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