Field Identification; Hcount Operation Example (Exc = 1); Field Identification Programming - Texas Instruments TMS320DM648 User Manual

BT.656 and Y/C Mode Field and Frame Operation
VCLKIN
VDIN[9−2]
Blanking Data
HSYNC
EXC=1
HRST=0
HCOUNT 842
VCOUNT
EXC=1
HRST=1
HCOUNT 778
VCOUNT
AVID
EXC=1
HRST=0
HCOUNT 720
VCOUNT
EXC=1
HRST=1
HCOUNT 0
VCOUNT

3.4.4 Field Identification

In order to properly synchronize to the source data stream and capture the correct fields, field
identification needs to be performed. Field identification is made using one of three methods: EAV, field
indicator input, or field detect logic. The field identification method is determined by the EXC, FLDD, and
FINV bits in VCxCTL.
EXC
0
0
1
1
In the BT.656 standard and in many Y/C standards, a field identification (F) bit is contained in EAV and
SAV codes embedded in the data stream. In the EAV field detect method, the F bit in the EAV of the first
line of every field is checked. If F = 0, then the current field is defined as field 1. If F = 1, then the current
field is defined as field 2. Depending on how the first line of a field is defined (as determined by the VRST
bit in VCxCTL) and the video stream being captured, the F value at the start of a field may not reflect the
actual field being supplied. The FINV bit in VCxCTL allows the detected field value to be inverted. (For
example, in BT.656 525/60 operation, the F bit changes to 0 to indicate field 1 on the fourth line of the
field. If the VRST bit is set so the line counter begins counting at line 1 of the field (the first EAV where V
is 1), then the F bit still indicates field 2 (F = 1) and needs to be inverted. If the VRST bit is set to start
counting lines beginning with the first active line (the first EAV where V is 0), the F value will have already
changed to indicate field 1 (F = 0) and no inversion is necessary.)
56 Video Capture Port
Figure 3-6. HCOUNT Operation Example (EXC = 1)
276
Blanking
843 844 857 0 63
n−1
779 780 793 794 857
n−1
721 722 735 736 799
n−1
1 2 15 16 79
Table 3-9. Field Identification Programming
VCxCTL Bit
FLDD Field Detect Method
0 EAV code
1 EAV code
0 Use FID input
1 Use field detect (from HSYNC and VSYNC inputs)
Active Video
64 119 120 121 122 123 124
n
0 55 56 57 58 59 60
800 855 856 857 0 1 2
80 135 136 137 138 139 140
n
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1440
840 842 842 843 844
776 777 778 779 780
n
718 719 720 721 722
n
856 857 0 1 2
n+1
SPRUEM1 – May 2007
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