LMH0031 Datasheet, PDF (13/31 Pages) National Semiconductor (TI) – SMPTE 292M/259M Digital Video Deserializer Descrambler with Video and Ancillary Data FIFOs

Device Operation (Continued)
FIGURE 2. Control Data Read Timing (2 read and 1 write cycle shown)
20179609
FIGURE 3. Control Data Write Timing
20179610
Ancillary Data Functions
The LMH0031 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 LMH0031 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 LMH0031 Ancillary Data FIFO also al-
lows storage of up to 8 shorter length messages with total
length not exceeding 259 words including all ID information.
Ancillary 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.
13
www.national.com