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MC144144 bảng dữ liệu(PDF) 9 Page - Motorola, Inc |
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MC144144 bảng dữ liệu(HTML) 9 Page - Motorola, Inc |
9 / 44 page MC144144 9 MOTOROLA The data channels for each field are transmitted in Line 21 of that field as a time multiplexed data stream. The start of a particular channel’s data stream is identified by the occur- rence of one of its unique command codes. Once a unique command code is received, all subsequent data is consid- ered to belong to that data channel until a unique command code is received for another data channel. The 7–bit ASCII table defines two types of information: printing and non–printing. Printable data are data bytes hav- ing values between x0100000 ($20) and x1111111 ($7F), where x represents the parity bit. Data bytes having values between x0000000 ($00) and x0011111 ($1F) are called non–printing characters, because they have no displayable character font in the standard ASCII table. Figure 2. Encoded Composite Video Signal 10.50 ± 0.5 µs 12.910 µs 4.15 ± 0.1 µs 33.764 µs 0.12 µs 2.0 µs 10.076 µs 1 2 3 4 5 6 7 8 9 10 1112 13 14 15 16 17 18 19 20 212223 24 2526 CHARACTER 1 CHARACTER 2 b1 b2 b4 b6 b3 b5 b7 b1 b2 b4 b6 b3 b5 b7 P A R I T Y P A R I T Y Displayable Character Set The specifications define a modified ASCII table character set where eight of the alphanumeric characters have been changed to provide some non–English characters. Also, 15 additional characters are defined by special character com- mands. The changes in the ASCII table characters are shown in Table 1. Table 1. Modifications to the ASCII Characters ç Hex Code ASCII Character Line-21 Character 2A * a ′ 5C \ e ′ 5E ^ i ′ 5F o ′ 60 ’ u ′ 7D } N 7E ~ n ~ ~ 7B { c Fifteen additional displayable characters are sent by trans- mitting a two–byte code. The sixteenth code provides a transparent space. The byte pair has a non–printing charac- ter followed by a printing character, where the non–printing character is $11 for Language 1 and $19 for Language 2. The printing character determines the special character font that is displayed according to Table 2. Commands and Special Information Data channel commands and special information are transmitted as two–byte pairs consisting of a non–printing character followed by a printing character. The two bytes of the pair must be transmitted in the same field, and the pair is transmitted twice in successive frames. This redundancy provides some immunity to noise errors for control informa- tion. Throughout the Line 21 system, bit 4 of the non–printing character identifies the language. Bit b4 = 0 signifies Lan- guage 1 commands and b4 = 1 signifies Language 2. The non–printing characters used in the Line 21 system are $10 through $17 for Language 1 and $18 through $1F for Lan- guage 2. Table 2. Additions to the ASCII Characters Print Character 30 ® 31 ° 32 1/2 33 ¿ 34 ™ 35 ¢ 36 o 37 “1/8 note” music symbol 38 a 39 “Transparent Space” 3A e 3B a 3C e 3D l 3E o 3F u ^ ^ ^ ^ ^ |
Số phần tương tự - MC144144 |
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Mô tả tương tự - MC144144 |
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