ASTRO VG-876, Инструкция по эксплуатации

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Chapter 11 FUNCTIONS AVAILABLE WITH TV STANDARD SIGNALS
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11.2. Closed captions/V-Chip
11.2.1. Description and specifications
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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).
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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.
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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, PAL-M, PAL-Nc
Note) When 625-line timing (PAL, PAL-Nc) is output, the caption data is superimposed on the 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).
Start Bit Character One Clock Run-In
Character Two
s1 s2 s3 b0 b1 b2 b3 b4 b5 b6 p1 b0 b1 b2 b3 b4 b5 b6 p2
50IRE
0IRE
LSB LSB
Closed Caption / V-Chip (21Line System)