accessDTV

The excitement around digital television (DTV) has been
growing steadily for several years. If you have been to any
of the major electronics stores recently, you have probably
noticed shelves filled with digital television sets.

At the same time, television stations have been quietly
launching their digital transmitters. The stations and the
networks have been outfitting their studios and trucks with
the equipment they need to shoot, record and edit with purely
digital signals. Almost all prime-time shows and sporting
events are now digital.

In most major cities, you can receive digital broadcasts. For
example, in San Jose, CA, you can receive about a dozen DTV
broadcasts. Even in a relatively small city like Raleigh, NC,
you can receive four stations. More than 100 million
Americans are able to receive at least one digital broadcast,
but far fewer than a million currently do. The main barrier
has been the price and complexity of home DTV equipment.

AccessDTV Features
The accessDTV card has a number of interesting features:

* It allows you to receive all of the DTV stations in
your area on your PC.
* It allows you to display the picture you receive in
a window on your computer monitor's screen, full on your
computer monitor's screen or externally on a DTV display.
* It provides personal video recording that allows you to
record DTV broadcasts onto your hard disk for later viewing.
* It provides a service that gives you a program guide,
listings for digital broadcasts in your area and links to
content-related Web sites.

DTV technology and programming is advancing quickly, and this
card lets you experience it all.

DTV

If you have read How Digital Television Works, then you are
familiar with the world of DTV. Here is a quick summary of
the important points:

* Broadcasters in your area have each been allocated
a new channel for their DTV broadcasts.

* The broadcasters each transmit a 19.39-Mbps stream of
digital data. This signal contains television programs
compressed using the MPEG-2 compression system.

* DTV shows can be broadcast at several different
resolutions:
o 480p - The picture is 704x480 scan lines sent at
60 complete frames per second.
o 720p - The picture is 1280x720 scan lines sent at
60 complete frames per second.
o 1080i - The picture is 1920x1080 scan lines sent
at 60 interlaced frames per second (30 complete frames per
second).

* Broadcasters can transmit either a single 1080i
high-definition channel that consumes the entire 19.39-Mbps
stream, or several different sub-channels by encoding
multiple programs at 480p resolution and lower bit rates.

For example, the DTV station 53 can have sub-channels
named 53.1, 53.2 and 53.3. accessDTV can record and play back
the sub-channels.

The accessDTV Digital­ Media Receiver Solution consists of
hardware and software. The hardware is a PCI card that you
install inside your PC. The software controls the card and
allows you to tune in and view DTV broadcasts in your area,
using either your computer monitor or an external HDTV
display.

AccessDTV Card Components

The following figure shows you a block diagram of the
components on the accessDTV PCI card:

The tuner receives the signal from the antenna and tunes in a
single channel. The demodulator retrieves the 19.39-Mbps
digital stream from the channel. The MPEG decoder
decompresses the MPEG encoding and separates subchannels. The
signal then goes to either the connectors on the board that
connect to a DTV monitor, or to the computer's video card
directly. MPEG signals and sound information can go through
the PCI bus to the hard disk and sound card, respectively.

The two most important components on the accessDTV card are:

* The digital tuner
* The MPEG-2 decoding system

By connecting a standard UHF/VHF antenna to the accessDTV
card, you can tune in any of the 69 DTV channels. (In
a typical city, there will be from three to 10 DTV channels
on the air.) The tuner pulls the 19.39-Mbps data stream off
the channel you choose.

The MPEG-2 decoder circuit decodes this data stream and
separates any sub-channels so that you can view them. This is
the most important part of the card because it offloads all
of the MPEG-2 decoding from your CPU.

The 19.39-Mbps stream is so complex that it would totally
consume a Pentium 4 processor running at 1.5 gigahertz (GHz).
The accessDTV card contains a custom processor specifically
tuned for MPEG-2 decoding. With the accessDTV card handling
decompression, only about 5 percent of your computer's CPU
power is spent displaying the digital image on the screen.
From your computer monitor, you can watch a DTV broadcast in
one window and do anything you want in other windows without
even knowing that the card is running.

The card also contains a cable-ready and NTSC
off-the-air-ready analog tuner. You can connect the coax from
your cable system or a standard TV antenna and receive analog
channels 2 through 83 as you would on any normal TV. You can
also view these channels in a window on your computer screen.

Connectors
The accessDTV card comes with a collection of connectors that
you use to accept video input and generate audio/video output.
This diagram shows you the connectors:

Here's what these connectors do:

* Analog in - This accepts analog video input. The input
can be an analog-TV antenna, a feed from the cable company,
or a channel-3 input from something like a VCR or DVD player.

* Digital in - This accepts digital video input.
Typically, this would be the Yagi antenna collecting the
digital broadcasts in your community, but it could also be
a cable from a digital satellite receiver.

* Dolby Digital Surround Sound (AC-3) output - This is
the output for digital sound. Typically, you would connect
this to your 5.1-channel home-theater sound system.

* PC Video passthru in

* Video output - This looks like a standard VGA
connector. You can use a cable to connect this to the
component video input of any supported digital display,
including DTV sets. In this case, the card acts as the
display's digital receiver.

There are two typical ways that you might connect the card in
your home: for computer-only viewing or for HDTV-display
viewing.

Viewing Methods

Computer-only Viewing
Let's say that you do not own an HDTV display right now, and
you simply want to watch HDTV broadcasts on your computer's
monitor. You would do the following:

1. Connect a standard UHF/VHF antenna to the digital video
input on the accessDTV card.
2. Connect the cable that comes with the accessDTV card
between the card and your normal video card.
3. Run the accessDTV application, choose your channel and
enjoy the broadcast. You can watch DTV in a window or
full-screen on your computer monitor.

HDTV-display Viewing
Let's say that you own an HDTV display and a home-theater
sound system, and you want to watch HDTV broadcasts on your
HDTV display. This means that you want to use your accessDTV
card as the digital receiver for your HDTV display. You would
do the following:

1. Connect a standard DTV antenna to the digital video
input on the accessDTV card.
2. Connect the cable that comes with the accessDTV card
between the card and your normal video card.
3. Connect the external HDTV display to the XVGA connector
on the accessDTV card using a standard XVGA-to-RGB cable.
4. Connect the home-theater sound system to the
serial-digital output on the accessDTV card.
5. Run the accessDTV application, choose your channel and
enjoy the broadcast. You can watch DTV on the external HDTV
display, or in a window or full screen on your computer
monitor.