Specifications

CHAPTER 1
Introduction
8 Optional Features
The features of the FM radio tuner are
■ the ability to receive and display FM radio frequencies
■ the ability to scan and search stations up and down the frequency spectrum
■ step frequency
■ a DX mode to tune out harmonic spillover from other stations
■ a stereo/mono station indicator
■ preset station programming
The TV and FM radio tuner module is available in versions for NTSC, PAL, and SECAM
television systems.
The TV picture appears in its own window. The default size of the window is 320-by-240
pixels. The user can resize the TV window up to a maximum size of 640-by-480 pixels or
down to a minimum size of 160-by-120 pixels. The resolution of the TV picture does not
increase at the larger window sizes; instead, the image is expanded by either doubling
the size of the pixels or by two-dimensional linear interpolation.
The TV tuner module works in conjunction with the video input module, which converts
the video data into digital YUV format and stores it in the display buffer.
The TV tuner comes with a remote control device similar to the one used with the
Macintosh TV computer. The user can switch channels either by using the remote control
or by typing the channel numbers on the keyboard. The user can toggle between the
current and previous channel by pressing the Tab key on the keyboard. Each time the
channel changes, the computer displays the channel name (assigned by the user) on the
picture in the video window.
The user can customize the operation of the TV tuner by adding or removing TV
channels that are unused or unwanted. The computer can program the channels
automatically, scanning through all available channels and disabling those that do not
have a valid signal. When the user then scans for the next channel by using the remote
control or the Tab key on the keyboard, the tuner skips the disabled channels.
The software that supports the TV tuner module is an application called Apple Video
Player. The application includes password protection for the disabled channels. Parents
might use this feature to prevent children from watching undesirable channels.
Why YUV Looks Clearer
You may be wondering how the digital YUV format
used in the Macintosh Performa 6400 computer
provides a clearer TV picture than the RGB format
used in the Macintosh TV computer—after all, picture
information can be freely converted between the two
formats. The difference is due to the way the bits are
allocated. The RGB format used in the Macintosh TV is
a 16-bit format using 5 bits each for red, green, and
blue, with the remaining bit unused. The YUV format
used in the Macintosh Performa 6400 computer is also
a 16-bit format, with 8 bits for the Y (luminance)
channel and 8 bits for the U and V (chrominance)
channels to share by multiplexing. The YUV format
looks clearer because the YUV format carries more
levels of luminance information.