Not only image and sound signals can be transmitted via HDMI, but also a lot of other data. The devices exchange various data and commands via it. CEC (Consumer Electronics Control) also uses an HDMI connection. The goal of CEC is that you can control important functions of the connected device with the TV remote control. This makes operation easier. To do this, the connected HDMI devices must support CEC. CEC is specified for a maximum of 15 devices and one television as HDMI-CEC master. Some manufacturers limit CEC to 10 devices. The support of the protocol can be very different, there are different commands. The most important are:
- Volume control, especially when using the Audio Return Channels (ARC)
- Transmission of device names
- Automatic switching on of connected devices
- One Touch Play (automatically switch source and start playback)
- Automatic switching to active source
- Playback controls (forward/backward, pause, play)
- System stand-by (all devices on stand-by at the same time)
- Timer control of recording devices
- Other functions can often be configured, take a look at the menu and manual of your television
For example, if you insert a Blu-Ray disc into the player and start playback, the television and sound system should switch on automatically and switch to the correct HDMI input. This usually works very well for devices from the same manufacturer and similar years of construction. If the implementation of CEC differs too much, functions are omitted. The manufacturers designate CEC differently. On the one hand for marketing reasons, but also to differentiate yourself from the functions of other manufacturers.
HDMI-CEC from the TV manufacturers
| SURNAME | MANUFACTURER |
|---|---|
| Anynet+ | Samsung |
| Aquos Link | Sharp |
| Bravia Link | Sony |
| Digital Link | basic |
| EasyLink | Phillips |
| Regza Link | Toshiba |
| Simplink | LG |
| TechniLink | TechniSat |
| VieraLink | panasonic |
During the HDMI handshake during switching on or connecting, the television exchanges information with the other HDMI devices about which functions are supported and assigns addresses for communication. This also works with devices that are switched off but are connected via HDMI. When the CEC is active, the HDMI sources register with the television. This exchange overflows pins 13 the HDMI connection.
Some devices or functions can only be triggered via addressed control commands. Such devices need their own address for this. A device obtains an address by attempting to ping devices connected via HDMI. If the ping is not confirmed, i.e. the address is free, the device claims the address for itself. If the ping is confirmed, the device tries another address. This is often a source of error, namely when devices are later added or removed from the HDMI chain.
The master device uses these addresses to send commands to specific target devices. When a master device sends a command, it is sent to all devices in the HDMI chain. The target device with the appropriate address will respond to the command, while the other devices will ignore it. In addition, there is also the concept of broadcast address, which allows the master to address all devices at once, for example to turn off all devices connected to the HDMI chain.
restrictions
Because CEC provides exactly one device (typically a television) as the central element (HDMI CEC Master), it does not work reliably in other configurations - for example without a television (when listening to music) or with 2 televisions. Therefore, HDMI splitters usually do not support control via HDMI CEC. Because the system is not designed for 2 or more televisions. The TV can also not address 2 sound systems, but only one. Because this can cause malfunctions, HDMI CEC can be switched off on the television.
A DisplayPort connection is becoming increasingly common on monitors and PC graphics cards. This port can also be used for HDMI with a simple adapter, but does not transmit CEC control. So you can't use CEC with a DisplayPort (or USB C Alternate Mode).