adv7314 Analog Devices, Inc., adv7314 Datasheet - Page 63

• Manufacturer Part Number: adv7314
• Description: Multiformat 216 Mhz Video Encoder With Six Nsv 14-bit Dacs
• Manufacturer: Analog Devices, Inc.

APPENDIX 3—SD CLOSED CAPTIONING
[Subaddress 51h–54h]
The ADV7314 supports closed captioning conforming to the
standard television synchronizing waveform for color transmis-
sion. Closed captioning is transmitted during the blanked active
line time of Line 21 of the odd fields and Line 284 of 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 a Logic Level 1 start bit. 16 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 [Address 53h–54h].
The ADV7314 also supports the extended closed captioning
operation, which is active during even fields and is encoded on
Scan Line 284. The data for this operation is stored in the SD
closed captioning registers [Address 51h–52h].
All clock run-in signals and timing to support closed captioning
on Lines 21 and 284 are generated automatically by the ADV7314.
All pixels inputs are ignored during Lines 21 and 284 if closed
captioning is enabled.
REV. 0
50 IRE
40 IRE
FREQUENCY = F
REFERENCE COLOR BURST
AMPLITUDE = 40 IRE
10.5
Figure 66. Closed Captioning Waveform, NTSC
10.003 s
(9 CYCLES)
0.25 s
SC
= 3.579545MHz
27.382 s
CLOCK RUN-IN
7 CYCLES OF
0.5035MHz
12.91 s
–63–
FCC Code of Federal Regulations (CFR) 47 section 15.119
and EIA608 describe the closed captioning information for
Lines 21 and 284.
The ADV7314 uses a single buffering method. This means that
the closed captioning buffer is only one byte deep, therefore
there will be no frame delay in outputting the closed captioning
data unlike other two byte deep buffering systems. The data
must be loaded one line before (Line 20 or Line 283) it is out-
put 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) every field. If no new
data is required for transmission, 0s must be inserted in both
data registers, which is called nulling. It is also important to load
control codes, all of that are double bytes on Line 21 or a televi-
sion 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 in order to get end-of-caption 2-byte
control code to land in the same field.
S
T
A
R
T
D0–D6
BYTE 0
ASCII CHARACTERS
TWO 7-BIT + PARITY
33.764 s
(DATA)
P
A
R
Y
T
I
D0–D6
BYTE 1
P
A
R
T
Y
I
ADV7314