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DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

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To determine whether a line that is<br />

a candidate for a digitized ancillary<br />

signal actually contains such a signal,<br />

examine every chroma/luma pair for<br />

{200 h, 40 h}: If any pair is unequal to<br />

these values, a digitized ancillary<br />

signal is present.<br />

SMPTE 291M, Ancillary Data<br />

Packet and Space Formatting.<br />

Ancillary data<br />

In 4:2:2 SDTV, and in HDTV, ancillary data is permitted<br />

immediately after any EAV (HANC), or immediately<br />

after SAV (VANC) on a line containing neither active<br />

picture nor digitized ancillary data. (In 576i, ancillary<br />

data is limited to lines 20 through 22 and 333 through<br />

335.) An ancillary packet is introduced by an ancillary<br />

data flag (ADF) comprising the three-word sequence {0,<br />

3FFh, 3FFh}. In 4f SC SDTV, ancillary packets are permitted in the<br />

synctip interval, immediately following the five-word<br />

TRS-ID sequence. Ancillary packets are also permitted<br />

in certain regions of the vertical interval; see<br />

SMPTE 259M. An ancillary packet is introduced by an<br />

ADF comprising the single word 3FF h.<br />

An ANC packet must not interfere with active video, or<br />

with any TRS, SAV, or EAV. Multiple ANC packets are<br />

allowed, provided that they are contiguous. Certain<br />

ANC regions are reserved for certain purposes; consult<br />

SMPTE 291M.<br />

An ancillary packet comprises the 3-word (4:2:2) or<br />

1-word (4f SC) ADF, followed by these elements:<br />

• A one-word data ID (DID)<br />

• A one-word data block number (DBN) or secondary<br />

DID (SDID)<br />

• A one-word data count (DC), from 0 to 255<br />

• Zero to 255 user data words (UDW)<br />

• A one-word checksum (CS)<br />

Each header word – DID, DBN/SDID, and DC – carries<br />

an 8-bit value. Bit 8 of each header word is parity,<br />

asserted if an odd number of bits 7 through 0 is set,<br />

and deasserted if an even number of bits is set. Bit 9 is<br />

coded as the complement of bit 8. (Codewords having<br />

8 MSBs all-zero or all-one are thereby avoided; this<br />

prevents collision with the 0 h and 3FF h codes used to<br />

introduce TRS and ANC sequences.)<br />

CHAPTER 33 DIGITAL SYNC, TRS, ANCILLARY DATA, AND INTERFACE 395

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