adv7194 Analog Devices, Inc., adv7194 Datasheet - Page 47

• Manufacturer Part Number: adv7194
• Description: Professional Extended-10? Video Encoder With 54 Mhz Oversampling
• Manufacturer: Analog Devices, Inc.

The ADV7194 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 seven-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. Sixteen bits of data
follow the start bit. These consist of two eight-bit bytes, seven
data bits, and one odd parity bit. The data for these bytes is
stored in Closed Captioning Data Registers 0 and 1.
The ADV7194 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 Closed
Captioning Extended Data Registers 0 and 1.
All clock run-in signals and timing to support Closed Captioning
on Lines 21 and 284 are generated automatically by the ADV7194
All pixels inputs are ignored during Lines 21 and 284 if closed
captioning is enabled.
40 IRE
50 IRE
FREQUENCY = F
AMPLITUDE = 40 IRE
REFERENCE COLOR BURST
10.5
10.003 s
(9 CYCLES)
0.25 s
SC
= 3.579545MHz
27.382 s
CLOSED CAPTIONING
(CLOCK RUN-IN)
APPENDIX 2
OF 0.5035 MHz
7 CYCLES
12.91 s
FCC Code of Federal Regulations (CFR) 47 Section 15.119
and EIA608 describe the closed captioning information for Lines
21 and 284.
The ADV7194 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-
putted 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, 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
which 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
TWO 7-BIT + PARITY
ASCII CHARACTERS
33.764 s
(DATA)
P
A
R
T
Y
I
D0–D6
BYTE 1
P
A
R
T
Y
I
ADV7194