ADV7181B
Rev. B | Page 36 of 100
AV CODE INSERTION AND CONTROLS
This section describes the I
2
C-based controls that affect:
•
Insertion of AV codes into the data stream.
•
Data blanking during the vertical blank interval (VBI).
•
The range of data values permitted in the output data
stream.
•
The relative delay of luma vs. chroma signals.
Some of the decoded VBI data is being inserted during the
horizontal blanking interval. See the Gemstar Data Recovery
section for more information.
BT656-4 ITU Standard BT-R.656-4 Enable, Address 0x04[7]
The ITU has changed the position for toggling of the V bit
within the SAV EAV codes for NTSC between Revision 3 and
Revision 4. The BT656-4 standard bit allows the user to select
an output mode that is compliant with either the previous or the
new standard. For more information, review the standard at
www.itu.int.
The standard change affects NTSC only and has no bearing on
PAL.
When BT656-4 is 0 (default), the BT656-3 specification is used.
The V bit goes low at EAV of Line 10 and Line 273.
When BT656-4 is 1, the BT656-4 specification is used. The
V bit goes low at EAV of Line 20 and Line 283.
SD_DUP_AV Duplicate AV Codes, Address 0x03[0]
Depending on the output interface width, it can be necessary to
duplicate the AV codes from the luma path into the chroma path.
In an 8-bit-wide output interface (Cb/Y/Cr/Y interleaved data),
the AV codes are defined as FF/00/00/AV, with AV being the
transmitted word that contains information about H/V/F.
In this output interface mode, the following assignment takes
place: Cb = FF, Y = 00, Cr = 00, and Y = AV.
In a 16-bit output interface where Y and Cr/Cb are delivered via
separate data buses, the AV code is over the whole 16 bits. The
SD_DUP_AV bit allows the user to replicate the AV codes on
both busses, so the full AV sequence can be found on the Y bus
and on the Cr/Cb bus. See Figure 18.
When SD_DUP_AV is 0 (default), the AV codes are in single
fashion (to suit 8-bit interleaved data output).
When SD_DUP_AV is 1, the AV codes are duplicated (for
16-bit interfaces).
VBI_EN Vertical Blanking Interval Data Enable,
Address 0x03[7]
The VBI enable bit allows data such as intercast and closed
caption data to be passed through the luma channel of the
decoder with a minimal amount of filtering. All data for Line 1
to Line 21 is passed through and available at the output port.
The ADV7181B does not blank the luma data, and auto-
matically switches all filters along the luma data path into their
widest bandwidth. For active video, the filter settings for YSH
and YPK are restored.
Refer to the BL_C_VBI Blank Chroma during VBI section for
information on the chroma path.
When VBI_EN is 0 (default), all video lines are filtered/scaled.
When VBI_EN is 1, only the active video region is
filtered/scaled.
Y DATA BUS
00
AV
Y
FF
00
00
AV
Y
FF
Cr/Cb DATA BUS
00
00
AV
Cb
FF
00
Cb
AV CODE SECTION
AV CODE SECTION
FF
00
00
AV
Cb
AV CODE SECTION
Cb/Y/Cr/Y
INTERLEAVED
8-BIT INTERFACE
16-BIT INTERFACE
16-BIT INTERFACE
SD_DUP_AV = 1
SD_DUP_AV = 0
04984-018
Figure 18. AV Code Duplication Control
