ADV7393 datasheet(70/96 Pages) AD

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ADV7390/ADV7391/ADV7392/ADV7393

Rev. 0 | Page 70 of 96

APPENDIX 3–SD CLOSED CAPTIONING

Subaddress 0x91 to Subaddress 0x94

The ADV739x supports closed captioning conforming to the

standard television synchronizing waveform for color

transmission. When enabled, 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 can be

enabled using Subaddress 0x83, Bits[6:5].

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 1 start bit. Sixteen bits of data follow the start

bit. The data consists of two 8-bit bytes (seven data bits, and one

odd parity bit per byte). The data for these bytes is stored in SD

closed captioning registers (Subaddress 0x93 to Subaddress 0x94).

The ADV739x also supports the extended closed captioning

operation, which is active during even fields and encoded on

Line 284. The data for this operation is stored in SD closed

captioning registers (Subaddress 0x91 to Subaddress 0x92).

The ADV739x automatically generates all clock run-in signals

and timing that support closed captioning on Line 21 and 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) Title 47 Section

15.119 and EIA-608 describe the closed captioning information

for Line 21 and Line 284.

The ADV739x 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

10.5 ± 0.25µs

12.91µs

7 CYCLES OF

0.5035MHz

CLOCK RUN-IN

REFERENCE COLOR BURST

(9 CYCLES)

FREQUENCY = FSC = 3.579545MHz

AMPLITUDE = 40 IRE

50 IRE

40 IRE

10.003µs

27.382µs

33.764µs

BYTE 1

BYTE 0

TWO 7-BIT + PARITY

ASCII CHARACTERS

(DATA)

Figure 101. SD Closed Captioning Waveform, NTSC

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