At its core, the HDMI technology has high-speed and digital signaling system especially developed to manage extremely high amounts of digital data over a very effective and accurate cable. The connectors of the HDMI usually include 19 pins, each contributing to the reliability and quality of the digital audio and video signals you will receive on your TV or computer. Over half of the pins incorporate the TMDS technology, an amazing innovation that is intended to protect the data from degrading.
Therefore, whilst 6 of the TMDS pins ensure the fast transmission of the large uncompressed digital data, 2 pins have the role of a clock signal designed to recover data that is lost during conduction. The last TMDS pins represent shielded paired channels that ensure the data transmission incorporates very little EMI emissions and cross-talk.
The introduction of the 1.3 generation of cables on the market meant adding the consumer electronic control pin to the connector. Even though this is mostly an optional feature, the truth is that it is very useful as it allows the user to control any other attached device automatically. The CEC features along with the DDC one are also included in a separate pin that has the role of returning all the signals that are not received via the TMDS channels. The compatibility of signal transmission is ensured by the display data channel pin; a device also used for encryption and authentication.
The last 2 pins that can be found on the HDMI connector are the +5V power and the hot plug detect pins. As its name suggests, the power pin is intended for supplying a low current that is needed for reading the EDID memory that is usually found in the display. The hot plug detector is responsible with announcing to the user certain events, such as an unplugged cable.
It is important to note that some manufacturers do not include the hot plug detector in the design of the HDMI connector. However, according to the configuration of the HDMI cable the 18 pin cables are not allowed anymore. When this innovative technology first appeared on the market, the HPD pin was not implemented then. Nowadays, it is found in all the HDMI cables you will see in stores or online. The great thing about HDMI is that they manage to make the 18 pin connectors operate efficiently on devices with 19 pin slots, and the newer version will fit older configuration as well.