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3.2 BT.656 Video Capture Mode
The BT.656 capture mode captures 8-bit or 10-bit 4:2:2 luma and chroma data
multiplexed into a single data stream. Video data is conveyed in the order
Cb,Y,Cr,Y,Cb,Y,Cr, etc. where the sequence Cb,Y,Cr refers to co-sited luma
and chroma samples and the following Y value corresponds to the next lu-
minance sample. The data stream is demultiplexed and each component is
written in packed form into separate FIFOs for transfer into Y, Cb, and Cr buff-
ers in DSP memory. (This is commonly called planar format.) The packing and
order of the samples is determined by the sample size (8-bit or 10-bit) and the
selected endianess of the DSP.
The ITU-BT.656 standard provides for either 8-bit or 10-bit component sam-
ples. When 10-bit samples are used, the 2 least significant bits are considered
fractional values. Thus for 8-bit operation, input data is aligned to the most sig-
nificant bits (9–2) of the input and the two least-significant bits are ignored.
In BT.656 video capture mode, data bytes in which the 8 most significant bits
are all set to 1 (FF.0h, FF.4h, FF.8h, FF.Ch) or are all set to 0 (00.0h, 00.4h,
00.8h, 00.Ch) are reserved for data identification purposes and consequently,
only 254 of the possible 256 8-bit words (or 1016 of 1024 10-bit words) may
be used to express signal value.
3.2.1
BT.656 Capture Channels
In dual channel operation, the video port can support capture of two BT.656
data streams or one BT.656 data stream and one raw data stream. In the latter
case, the BT.656 stream may occur on either Channel A or Channel B. In either
case, the BT.656 stream(s) must have embedded timing reference codes and
the appropriate VCTL input must be used as a CAPEN signal.
If the port is configured for single channel operation, capture will take place on
Channel A only. The unused half of the VDATA bus may be used for GPIO or
for another peripheral function. For single channel operation, non-standard
BT.656 data streams without embedded timing reference codes are supported
through the use of the timing control (VCTL) input signals.
SPRU629
BT.656 Video Capture Mode
Video Capture Port
3-3
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