The Custom Integrator Show Installment 01F is live.  We dive a little further into the inner workings of HDMI.  We specifically look at the wires inside of the sheath and their usage where timing is of the essence.  When we are talking about hundredths and thousandths of an inch, each twist and turn inside of the HDMI cable influences the success of the content delivery.  As always, there is a lot more information in the associated Podcast.


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It is important to understand the HDMI standards, what connections are made inside of the wire, and what parameters influence the connection.  This accompanying diagram details the HDMI 1.3 pin outs (we discuss HDMI 1.4 in a subsequent Installment).  Notice that the three Transition Minimized Differential Signaling (TMDS) lines also have an associated clock line.  If the twists inside of the cable are not exact or the length of any one of the lines is not precise, the link may fail to work properly.  The electrical characteristics of the wire play a huge role in keeping all of these high speed signals in synch and not all cables are the same.  Looking for the Digital Performance Level (DPL) rating systems logo helps debunk some of the myths around the goods and bads of most HDMI cables, so use that as one of your purchasing criteria.


We also discuss the 5.0 Volt DC line used for driving the electronics on the sink side for things like the initial Hot Plug Detect handshake in addition to obtaining the Enhanced Display ID (EDID) information used for optimizing the connection (when the device technically is “turned off”).  These electronics are critical to making a successful connection and the tolerances for the power to them is very tight.  There only is a 55 mA budget and if the voltage level drops below 4.7 Volts, you might as well forget having the link work correctly.  That is why it is so important for any long distance cables with active electronics to have its own power supply.  You cannot pull it off of the 5 Volt line built into the HDMI architecture, ever!

Below is another diagram depicting the architecture in more of a functional way.


This will be useful to reference as you listen to the Podcast.  For most savvy integrators, this information is second nature.  However, we hope that our discussions shed some new light on the characteristics of the HDMI interface and where things could go wrong.

The next Installment drills down into everyone’s favorite topic, High-bandwidth Digital Content Protection (HDCP).  After the Hot Plug Detect and the exchange of EDID information, setting up a secure and encrypted link is the next step in the process.  To me, it is amazing how much “activity” goes on between the source and the sink by just plugging the cable in.  There is a lot that could go wrong, but hopefully the more you understand about HDMI, the less risk you will induce into the chain, so stay tuned.


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