adv7322 Analog Devices, Inc., adv7322 Datasheet - Page 69

• Manufacturer Part Number: adv7322
• Description: Multiformat 11-bit Hdtv Video Encoder
• Manufacturer: Analog Devices, Inc.

Preliminary Technical Data
APPENDIX 3—SD CLOSED CAPTIONING
[Subaddresses 0x51 to 0x54]
The ADV7322 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 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 [Addresses 0x53 to 0x54].
The ADV7322 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 [Addresses 0x51 to 0x52].
All clock run-in signals and timing to support closed captioning
on Lines 21 and 284 are generated automatically by the
ADV7322. All pixels inputs are ignored during Lines 21 and 284
if closed captioning is enabled.
50 IRE
40 IRE
FREQUENCY = F
REFERENCE COLOR BURST
AMPLITUDE = 40 IRE
10.5 r 0.25Ps
10.003Ps
(9 CYCLES)
SC
= 3.579545MHz
Figure 97. Closed Captioning Waveform, NTSC
27.382Ps
Rev. PrA | Page 69 of 88
CLOCK RUN-IN
7 CYCLES OF
0.5035MHz
12.91Ps
FCC Code of Federal Regulations (CFR) 47 section 15.119 and
EIA608 describe the closed captioning information for Lines 21
and 284.
The ADV7322 uses a single buffering method. This means that
the closed captioning buffer is only 1 byte deep; therefore, there
will be 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 will load the new data
(two bytes) in every field. If no new data is required for
transmission, 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, or a TV will not recognize
them. If there is a message like “Hello World” that has an odd
number of characters, it is important to pad it out to even to get
“end of caption” 2-byte control code to land in the same field.
A
R
S
T
T
D0–D6
TWO 7-BIT + PARITY
ASCII CHARACTERS
BYTE 0
33.764P s
(DATA)
A
R
P
T
Y
I
D0–D6
BYTE 1
A
R
P
T
Y
I
ADV7322