參數(shù)資料
型號： ADV7344BSTZ
廠商： ANALOG DEVICES INC
元件分類： DAC
英文描述： Multiformat Video Encoder Six 14-Bit Noise Shaped Video DACs
中文描述： SERIAL INPUT LOADING, 14-BIT DAC, PQFP64
封裝： ROHS COMPLIANT, MS-026BCD, LQFP-64
文件頁數(shù)： 73/88頁
文件大小： 1078K
代理商： ADV7344BSTZ
ADV7344
APPENDIX 3—SD CLOSED CAPTIONING
Subaddress 0x91 to Subaddress 0x94
The ADV7344 supports closed captioning conforming to the
standard television synchronizing waveform for color
transmission. Closed captioning is transmitted during the
blanked active line time of Line 21 of the odd fields and
Line 284 of the even fields.
Closed captioning consists of a 7-cycle sinusoidal burst that is
frequency- and phase-locked to the caption data. After the clock
run-in signal, the blanking level is held for two data bits and is
followed by the Logic 1 start bit. Sixteen bits of data follow the
start bit. These consist of two 8-bit bytes, seven data bits, and one
odd parity bit. The data for these bytes is stored in the SD closed
captioning registers (Subaddress 0x93 to Subaddress 0x94).
The ADV7344 also supports the extended closed captioning
operation, which is active during even fields and encoded on
Scan Line 284. The data for this operation is stored in the SD
closed captioning registers (Subaddress 0x91 to Subaddress 0x92).
The ADV7344 automatically generates all clock run-in signals
and timing that support closed captioning on Line 21 and
Rev. 0 | Page 73 of 88
Line 284. All pixels inputs are ignored on Line 21 and Line 284
if closed captioning is enabled.
The FCC Code of Federal Regulations (CFR) 47 Section 15.119
and EIA-608 describe the closed captioning information for
Line 21 and Line 284.
The ADV7344 uses a single buffering method. This means that
the closed captioning buffer is only 1-byte deep. Therefore,
there is no frame delay in outputting the closed captioning data,
unlike other 2-byte deep buffering systems. The data must
be loaded one line before it is output on Line 21 and Line 284.
A typical implementation of this method is to use VSYNC to
interrupt a microprocessor, which in turn loads the new data
(2 bytes) in every field. If no new data is required for transmis-
sion, 0s must be inserted in both data registers; this is called
nulling. It is also important to load control codes, all of which
are double bytes, on Line 21. Otherwise, a TV does not
recognize them. If there is a message such as “Hello World”
that has an odd number of characters, it is important to add a
blank character at the end to make sure that the end-of-caption,
2-byte control code lands in the same field.
D0 TO D6
D0 TO D6
10.5 ± 0.25μs
12.91μs
7 CYCLES OF
0.5035MHz
CLOCK RUN-IN
REFERENCE COLOR BURST
(9 CYCLES)
FREQUENCY = F
= 3.579545MHz
AMPLITUDE = 40 IRE
10.003μs
50 IRE
40 IRE
27.382μs
33.764μs
BYTE 1
BYTE 0
TWO 7-BIT + PARITY
ASCII CHARACTERS
(DATA)
S
T
A
R
T
P
A
R
I
T
Y
P
A
R
I
T
Y
0
Figure 99. SD Closed Captioning Waveform, NTSC
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