The bus, known as the consumer electronics control (CEC) bus, is the basis for a new level of automatic control in HDMI-interfaced systems. With the recent release of a CEC compliance test specification and commercial CEC test equipment, consumer electronic companies are now poised to implement CEC in their products. In fact, new CECenabled products are expected to begin shipping in April 2006.
The basic technology of the CEC bus originated in Europe, on the SCART interface, where it’s been used with great success for many years. HDMI borrows and improves on the basic SCART technology, allowing AV products to discover and communicate with one another across a system. CEC makes possible global controls, which build on existing point-topoint E-DDC-based "plug & play" automation to minimize the number of IR remotes and key-presses required for basic operation of a system.
CEC assumes that all AV source products in a system are directly or indirectly connected to a “root” display. HDMI connections form an upside-down tree, with a display as the “root”, switches as “branches”, and various source products as “leaf” nodes. For example, CEC allows users to connect a mix of AV products, place a DVD into the player, press PLAY, and let CEC handle the rest.
CEC will automatically power-on the appropriate products, route the DVDplayer’s audio output through the AVR to attached speakers, and route the player’s motion picture to the Digital TV. Likewise, selecting a channel on the set-top-box will cause television audio to replace movie audio on the speakers and a TV picture to replace the motion picture on the Digital TV. Further, pressing the RECORD button on the recording device will cause the television program on the "root" to be automatically routed to and recorded on that device. In short, CEC enables automatic equipment discovery and simple "one touch" operation in HDMI-interfaced systems.
The CEC bus is a one-wire, “party line” that connects up to ten (10) AV devices through standard HDMI cabling. The CEC protocol includes automatic mechanisms for physical address (topology) discovery, (product type based) logical addressing, arbitration, retransmission, broadcasting, and routing control. Message opcodes support both device specific (e.g. set-top-box, DTV, and player) and general features (e.g. for power, signal routing, remote control pass-through, and on-screen display).