ASTRO VG-870B, Instruction Manual

Page: 290 / 579

272
5.2 Closed captions/V-Chip
5.2.1 Description and specifications
What does the closed caption (CC) function do?
Closed captioning was developed in the United States, and it provides broadcasts with subtitles for
the hearing impaired so that people who are deaf or hard of hearing can enjoy movies and news
programs.
The captions are “closed” in the sense that they are not displayed on the screen during normal
playback. Conversely, the Japanese-language subtitles and other such characters used with video
content which are “burned into” the images from the start are referred to as “open captions.”
Although closed captioning was originally developed as a technology for the hearing impaired, it is
currently attracting the attention of educators and language learners as a tool which helps develop
“listening.”
The CC subtitle data is superimposed onto line 21 (first field) and line 284 (second field) of the NTSC
output signals, and output. The subtitle data has two modes, captions and text. Another available
service is the Extended Data Service (EDS) which transmits titles, ratings and other program
information using line 284 (second field). The V-Chip described below uses the EDS function.
A total of 32 characters can be displayed per line by CC. There are 15 lines, but the maximum
number of lines is limited to 4 in the caption mode (CC1 to 4). All 15 lines can be displayed in the text
mode (T1 to 4).
( What does the V-Chip do?
The V-Chip refers to a semiconductor chip that blocks out TV programs containing
violence, bad language and sex situations.
“
V
”
refers to violence, and the viewing of
programs is blocked out according to the ratings which are categorized by the extremity of
the program content. Once the ratings are set in a receiver (TV set) which incorporates the
V-Chip function, the rating information of EDS is decoded, and whether the programs is to
be output to the screen is automatically determined.
( Specifications of closed caption/V-Chip
Closed caption/V-Chip supports the TV signals of the following systems.
Closed caption/V-Chip is superimposed onto the composite signals and Y/C signals.
•
NTSC-M, NTSC-J, NTSC-443
•
PAL-60, PAL, PAL-M, PAL-N, PAL-Nc
Note) When using VM-1812, if 625-line timing (PAL, PAL-N, PAL-Nc) is output, the caption
data is superimposed on the 23th line (335-line). In case of using VM-1812-B, it is
imposed on 21st line (334 line).
The closed caption/V-Chip waveform is shown below. Following the color burst come a sine
wave known as Clock Run-In and continues to the start bit. The start bit is always
“
001.
”
Two bytes of data (Char1, Char2) are sent for each line. Char1 and Char2 are decoded from
LSB, and an odd parity is usually added to MSB (bit 8).
･INCLUDEPICTURE "C:\\Documents and Settings\\k-mori.DASTRO1\\Application
Data\\Microsoft\\Word\\VG-870\\Data\\Waveform-CC-VChip.emf" \* MERGEFORMATINET \d ･･･