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.