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3.4.3 Horizontal Synchronization
Horizontal synchronization determines when the horizontal pixel/sample counter is reset. The EXC and
HRST bits in VCxCTL allow you to program the event that triggers the start of a line. The encoding of
these bits is shown in
HMode
0
1
2
3
HMode 0 is used for BT.656 or Y/C capture (with embedded control) and corresponds to the idea that
each line begins with the horizontal blanking period. It does not align with most standards that start
counting with the first active pixel; therefore, is only useful if capturing of HANC data before the SAV code
is desired. HMode 1 is the default mode and corresponds to most digital video standards by making the
first active pixel pixel0. It has the effect of associating horizontal blanking periods with the end of the
previous line rather than the beginning of the line, but this is only an issue if you try to capture HANC data.
In either mode, HCOUNT increments on every VCLKIN edge for Y/C operation and on every other
VCLKIN edge for BT.656 operation but only when CAPEN is active. HCOUNT operation for HMode 1 and
HMode 2 is shown in
HMode 2 and HMode 3 are used for BT.656 or Y/C capture without embedded EAV/SAV code and allow
alignment with either the beginning of the horizontal blanking period or the first active pixel, or the
beginning or end of horizontal sync depending on the VCTL1 input. When VCTL1 is configured as a
horizontal control input, no external CAPEN signal is available so the CAPEN signal is considered to
always be active. HCOUNT operation for HMode 3 and HMode 4 is shown in
operating as either HSYNC or AVID.
VCLKIN
VDIN[9−2]
EXC=0
HRST=0
HCOUNT
EXC=0
HRST=1
HCOUNT
VCOUNT
SPRUEM1 – May 2007
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Table
3-8.
Table 3-8. Horizontal Synchronization Programming
VCxCTL Bit
EXC
HRST
Horizontal Counter Reset Point
0
0
EAV code (H=1) - beginning of horizontal blanking.
0
1
SAV code (H=0) - Start of active video.
1
0
VCTL1 input active edge - beginning of horizontal blanking or horizontal sync
period. (VCTL1 must be configured as a horizontal control signal.)
1
1
VCTL1 input inactive edge - first active pixel on line or end of horizontal sync.
(VCTL1 must be configured as a horizontal control signal.)
Figure
3-5.
Figure 3-5. HCOUNT Operation Example (EXC = 0)
4
268
Blanking
EAV
Blanking Data
720 721 722 723
855 856 857
856 857
0
1
133 134 135 136 273 274
n−1
BT.656 and Y/C Mode Field and Frame Operation
4
1440
Active Video
SAV
One Line
0
1
2
One Line
n
Figure 3-6
for VCTL
EAV
Next Line
718 719 720 721 722 723
Next Line
854 855 856 857
0
1
n+1
Video Capture Port
55
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