ADV7321 datasheet(69/88 Pages) AD

69 / 88 page

ADV7320/ADV7321

Rev. 0 | Page 69 of 88

APPENDIX 3—SD CLOSED CAPTIONING

[Subaddresses 0x51 to 0x54]

The ADV7320/ADV7321 support 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 ADV7320/ADV7321 also support 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

ADV7320/ ADV7321. All pixels inputs are ignored during

Lines 21 and 284 if closed captioning is enabled.

FCC Code of Federal Regulations (CFR) 47 section 15.119 and

EIA608 describe the closed captioning information for Line 21

and Line 284.

The ADV7320/ADV7321 use 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 (2 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 such as “Hello World” that has an

odd number of characters, it is important to add a blank

character at the end so that the end-of-caption, 2-byte control

code lands in the same field.

D0–D6

10.5

± 0.25µs

12.91

µs

7CYCLES OF

0.5035MHz

CLOCK RUN-IN

REFERENCE COLOR BURST

(9 CYCLES)

FREQUENCY = FSC = 3.579545MHz

AMPLITUDE = 40 IRE

50 IRE

40 IRE

10.003

µs

27.382

µs

33.764

µ s

BYTE 1

BYTE 0

TWO 7-BIT + PARITY

ASCII CHARACTERS

(DATA)

Figure 98. Closed Captioning Waveform, NTSC

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