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3.6 Ancillary Data Capture
The BT.656 and some Y/C specifications includes provision for carrying ancillary
(nonvideo) data within the horizontal and vertical blanking regions. Horizontal
ancillary (HANC) data appears between the EAV code and SAV codes. Vertical
ancillary (VANC) data, also called vertical blanking interval (VBI) data, appears
during the active horizontal line portion of vertically blanking (for example, after
an SAV with V = 1).
3.6.1
Horizontal Ancillary (HANC) Data Capture
No special provisions are made for the capture of HANC data. HANC data may
be captured using the normal video capture mechanism by programming
VCXSTRT to occur before the SAV (when HCOUNT is reset by the EAV code)
or by programming VCXSTOP to occur past the EAV code (when HCOUNT
is reset by the SAV code). Note that the EAV code and any subsequent HANC
data will still be YCbCr separated. Software must parse the Y, Cb, and Cr
memory buffers to determine any HANC data presence and to reconstruct the
HANC data. The VCTHRLD value and DMA size must be programmed to
comprehend the additional samples. You must disable scaling and chroma re-
sampling when including the capture of HANC data to prevent data corruption.
3.6.2
Vertical Ancillary (VANC) Data Capture
VANC (or VBI) data is commonly used for such features as teletext and closed-
captioning. No special provisions are made for the capture of VBI data. VBI
data may be captured using the normal capture mechanism by programming
VCYSTART to occur before the first line of active video on the first line of
desired VBI data. (VCOUNT must be reset by an EAV with V = 1). Note that
the VBI data will be YCbCr separated. Software must parse the Y, Cb, and Cr
memory buffers to determine any VBI data presence and to reconstruct the
VBI data. You must disable scaling and chroma resampling when the capture
of VBI data is desired or the data will be corrupted by the filters.
SPRU629
Ancillary Data Capture
Video Capture Port
3-31
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