CLC031AVEC datasheet(13/31 Pages) NSC

13 / 31 page

Device Operation (Continued)

Ancillary Data Functions

The CLC031A can recover Ancillary Data from the serial

data stream. This Ancillary Data and related control charac-

ters are defined in the relevant SMPTE standards and may

reside in the horizontal and vertical blanking intervals. The

data can consist of different types of message packets in-

cluding audio data. The serial Ancillary Data space must be

formatted according to SMPTE 291M. The CLC031A sup-

ports Ancillary Data in the chrominance channel (C’r/

C’b) only for high-definition operation. Ancillary Data for

standard definition follows the requirements of SMPTE

125M.

The Ancillary Data FIFO is sized to handle a maximum

length ANC data Type 1 or Type 2 packet without the ANC

Flag, 259 words. Defined in SMPTE 291M, the packet con-

sists of the Ancillary Data Flag, a 3-word Data ID and Data

Count, 255 8- or 10-bit User Data Words and a Checksum.

The design of the CLC031A Ancillary Data FIFO also allows

storage of up to 8 shorter length messages with total length

not exceeding 259 words including all ID information. Ancil-

lary Data is copied from the data stream into the Ancillary

Data FIFO. The parallel Ancillary Data will still be present in

the parallel chroma output DV[9:0]. ancillary flag information

is not extracted into the FIFO.

Copying of ANC data from the video data into the FIFO is

controlled by the ANC Mask and ANC ID bits in the control

registers. A system of flags, ANC FIFO Empty, ANC FIFO

90% Full, ANC FIFO Full and ANC FIFO Overrun are used

to monitor FIFO status. The details and functions of these

and other control words are explained later in this datasheet.

20020109

FIGURE 2. Control Data Read Timing (2 read and 1 write cycle shown)

20020110

FIGURE 3. Control Data Write Timing

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