Convergence, or the merging of applications, features, and functions, has been an ongoing trend in consumer electronics and PCs. Such convergence is most notable at the system interface. One interface in particular—1394 (pronounced "thirteen ninety four")—has been very successful in bridging the gap between interface flexibility/capability and ease-of-use.
Otherwise known as Firewire or iLink, 1394 has been shipping for years in camcorders with DV capability. It's the standard plug-and-play interface for transferring DV-formatted A/V streams between digital camcorders and PCs, bringing a host of ease-of-use features and flexible capabilities to DV editing platforms.
Now, 1394 promises to bring these same features and capabilities right into everyone's living room through DTV and the DSTB. Care must be taken during the product definition and design phases to implement the 1394 interface correctly from both hardware and software perspectives.
System designers must know the relevant and appropriate standards impacting Firewire in DTV and DSTB. They also need to know what features and functionality to look for when selecting 1394 devices for their products.
The demand for digital-ready set-top boxes and TVs has grown rapidly with the advent of DTV content broadcasting from satellite and, more recently, cable and terrestrial sources. Digital A/V content is most often formatted in MPEG-2 or a derivative of it. The DirecTV system transport is a slightly modified version of the DVB system format.
As broadcast source material has evolved from analog to digital form, the front end of the receiving nodes has changed accordingly. But the I/O connections between the set-top-box receiver and the TV have largely re-mained analog, with high-end boxes simply moving from analog S-video to analog YUV component video. Firewire enables the transition from these classic point-to-point analog interfaces that only support analog A/V streams to an all-digital, networked interface capable of supporting digital A/V streams, as well as asynchronous data types, like computer file transfers.
DSTB architecture: 1394 can fit into the system architecture of a DSTB, serving as both a digital output and a digital input (Fig. 1). The output connection can go to digital recording devices, such as digital VHS decks or personal video recorders. Firewire also can serve as an input from those same digital recording devices, or even from popular digital video camcorders, provided that the set-top box can decode DV streams.
With the inherent ability to run multiple protocols across 1394 and support up to 64 nodes on a single 1394 bus, it's possible to network a DTV and DSTB with other popular consumer items, like a DVD player and an A/V receiver. For example, when receiving a movie with DTS or AC-3 encoded audio, this high-quality audio (in its native digital format) can be sent directly to an A/V receiver for surroundsound decoding, while the video in native MPEG format goes directly to a DTV for decoding—all across the same 1394 cables. Moreover, 1394's plug-and-play capability makes hooking all this equipment together, which has been a perennial nightmare for the average consumer, much easier.
The 1394 set-top box of Figure 1 shows an MPEG decoder that's really optional. Integrated DTVs (those with built-in digital tuner/demodulator capability) will have an MPEG decoder for receiving terrestrial ATSC broadcasts. So, including 1394 in the digital satellite/cable STB eliminates the need for an MPEG decoder in those boxes. Of course, during the transition from analog TVs to digital TVs, the MPEG decoder in the STB will be required in order to interface to legacy TVs.
An area of overlapped capabilities between DSTB and DTV, at least during the age of legacy connections to analog-only TVs, will be viewer control of channel selection, plus generating and controlling the program guide via OSD. The CEA standard, EIA-775-A, specifies the requirements of the 1394 interface between DSTB and DTV. This standard identifies two cases for service selection. With one, the source (the set-top box) controls the navigation and selection of program material. With the other, the DTV controls it.
When 1394 is used for the connection and the source device controls program navigation and selection, the CEA requires the DSTB to provide a single program transport stream to the DTV. DSTB designers should be sure the MPEG-2 demultiplexer/decoder has this ability when designing 1394 into the system.
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