ADV7180
When AUTO_PDC_EN is 1 (default), the ADV7180 automati-
cally determines the LTA and CTA values to have luma and
chroma aligned at the output.
BL_C_VBI, Blank Chroma During VBI, Address 0x04 [2]
Setting BL_C_VBI high, blanks the Cr and Cb values of all VBI
lines. This is done so any data that may arrive during VBI is not
decoded as color and is output through Cr and Cb. As a result,
it is possible to send VBI lines into the decoder, and then output
them through an encoder again, undistorted. Without this
blanking, any color that is incorrectly decoded would be
encoded by the video encoder, thus distorting the VBI lines.
LTA[1:0], Luma Timing Adjust, Address 0x27 [1:0]
The luma timing adjust register allows the user to specify a
timing difference between chroma and luma samples.
Note that there is a certain functionality overlap with the
CTA[2:0] register. For manual programming, use the
following defaults:
Setting BL_C_VBI to 0 decodes and outputs color during VBI.
Setting BL_C_VBI to 1 (default) blanks Cr and Cb values
during VBI.
•
•
•
CVBS input LTA[1:0] = 00
Y/C input LTA[1:0] = 01
YPrPb input LTA[1:0] = 01
RANGE, Range Selection, Address 0x04 [0]
AV codes (as per ITU-R BT.656, formerly known as CCIR-656)
consist of a fixed header made up of 0xFF and 0x00 values.
These two values are reserved and therefore are not to be used
for active video. Additionally, the ITU specifies that the
nominal range for video should be restricted to values between
16 to 235 for luma and 16 to 240 for chroma.
Table 58. LTA Function
LTA[1:0]
Description
00 (default)
No delay
01
10
11
Luma 1 clock (37 ns) late
Luma 2 clock (74 ns) early
Luma 1 clock (37 ns) early
The RANGE bit allows the user to limit the range of values
output by the ADV7180 to the recommended value range. In
any case, it ensures that the reserved values of 255d (0xFF) and
00d (0x00) are not presented on the output pins unless they are
part of an AV code header.
CTA[2:0], Chroma Timing Adjust, Address 0x27 [5:3]
The chroma timing adjust register allows the user to specify a
timing difference between chroma and luma samples. This may
be used to compensate for external filter group delay differences
in the luma vs. chroma path and to allow a different number of
pipeline delays while processing the video downstream. Review
this functionality together with the LTA[1:0] register.
Table 57. RANGE Function
RANGE
Description
16 ≤ Y ≤ 235
1 ≤ Y ≤ 254
0
16 ≤ C/P ≤ 240
1 ≤ C/P ≤ 254
1 (default)
The chroma can be delayed or advanced only in chroma pixel
steps. One chroma pixel step is equal to two luma pixels. The
programmable delay occurs after demodulation, where one can
no longer delay by luma pixel steps.
AUTO_PDC_EN, Automatic Programmed Delay Control,
Address 0x27 [6]
Enabling AUTO_PDC_EN activates a function within the
ADV7180 that automatically programs the LTA[1:0] and
CTA[2:0] to have the chroma and luma data match delays for
all modes of operation. If set, manual registers LTA[1:0] and
CTA[2:0] are not used. If the automatic mode is disabled (by
setting the AUTO_PDC_EN bit to 0), the values programmed
into LTA[1:0] and CTA[2:0] registers become active.
For manual programming, use the following defaults:
•
•
•
CVBS input CTA[2:0] = 011
Y/C input CTA[2:0] = 101
YPrPb input CTA[2:0] = 110
Table 59. CTA Function
When AUTO_PDC_EN is 0, the ADV7180 uses the LTA[1:0] and
CTA[2:0] values for delaying luma and chroma samples. Refer to
the LTA[1:0], Luma Timing Adjust, Address 0x27 [1:0] section
and the CTA[2:0], Chroma Timing Adjust, Address 0x27 [5:3]
section.
CTA[2:0]
Description
000
001
010
011 (default)
100
101
110
111
Not used
Chroma + 2 chroma pixel (early)
Chroma + 1 chroma pixel (early)
No delay
Chroma – 1 chroma pixel (late)
Chroma – 2 chroma pixel (late)
Chroma – 3 chroma pixel (late)
Not used
Rev. A | Page 42 of 112
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