When anyone in our family wants to watch a movie on our new HDTV, I usually have to help them operate the five remote controls that reside on our coffee table. If this scenario sounds familiar, there is some good news headed your way. A new feature of the HDMI (High Definition Multimedia Interface) link known as CEC (Consumer Electronic Control) is intended to make the home entertainment system useable by all family members. This article will define what CEC is and what it is not, explain the key features of interest to consumers of home entertainment products, describe details of the physical interface, and address some important system level hardware and software considerations. Design engineers embarking on a CEC-enabled design project should, of course, start with a diligent study of the latest HDMI specification.
While the general public may not be familiar with the term CEC, they may have heard of some of the leading consumer electronics industry makers' brand names for it. Among them are Sony's "Bravia Link," Panasonic's "Viera Link," and Sharp's "Aquos Link." The names may differ, but all support the CEC functionality described in the HDMI standard.
CEC is a single-wire, bidirectional interface intended to facilitate the control of any device on an HDMI network, as typified in Figure 1, with the remote control unit or on-device control buttons of any other device connected to the network. Defined as an optional feature in the HDMI specification, it is based on the AV Link function defined in the European SCART (Syndicat des Constructeurs d'Appareils Radiorcepteurs et Tlviseurs) specification. Table 1 describes some typical end-user CEC features.
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Figure 1: Typical All-HDMI Home Theatre
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Table 1: Some useful "End-User" CEC Features
Many of these end-user features require sending multiple messages over the CEC bus such as "Active Source," and "Routing Change," which support the CEC feature "Routing Control." This feature allows a device to play and become the active source by switching the TV's source input. If the TV is displaying another source at the time this command is used, it may place the other source into "stand-by" mode, depending on the implementation.
Those who have lost the DVD player's remote are in luck. Just pop in the DVD and push play on the front panel of the player. With a single push of the button, the following happens: the DVD player drawer closes, the TV and audio/video receiver (AVR) power-up, each device selects the correct HDMI port and the proper video and audio modes, and the DVD starts playing. Pretty cool.
There are some misconceptions about the current offerings of CEC-enabled products. In most current implementations, CEC commands only work with one brand; so unless the entire system is from the same manufacturer, it is impossible to simply pick up the TV remote and control the entire system without performing some programming of the TV remote. Fortunately, current industry trends are leading in this direction, and equipment vendors are beginning to cooperate with developers to share some of their proprietary commands. The CEC specification allows for customization and vendors have been using this to encourage the end user to purchase full systems of their own brand's equipment.
Next: CEC physical interface and timing