MC144144P 查看數據表（PDF） - Motorola => Freescale
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MC144144P Datasheet PDF : 44 Pages
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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.
10.50 ± 0.5 µs
10.076 µs
12.910 µs
4.15 ± 0.1 µs
33.764 µs
P
P
b1
b2 b3
b4
b5
b6
b7
A
R
b1 b2
b3 b4 b5
b6
b7
A
R
I
I
T
T
Y
Y
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
CHARACTER 1
CHARACTER 2
0.12 µs
2.0 µs
Figure 2. Encoded Composite Video Signal
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
Hex
Code
2A
5C
5E
5F
60
7B
7D
7E
ASCII
Character
*
\
^
’
{
}
~
Line-21
Character
a′
e′
i′
o′
u′
çc
N~
~n
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
30
31
32
33
34
35
36
37
38
39
3A
3B
3C
3D
3E
3F
Character
®
°
1/2
¿
™
¢
o
“1/8 note” music symbol
a
“Transparent Space”
e
a^
e^
^l
o^
u^
MOTOROLA
MC144144
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