ADV7181BCP Analog Devices Inc, ADV7181BCP Datasheet - Page 53

• Manufacturer Part Number: ADV7181BCP
• Description: IC VIDEO DECODER NTSC 64-LFCSP
• Manufacturer: Analog Devices Inc
• Type: Video Decoderr

Specifications of ADV7181BCP

• Applications: Recorders, Set-Top Boxes
• Voltage - Supply, Analog: 3.15 V ~ 3.45 V
• Voltage - Supply, Digital: 1.65 V ~ 2 V
• Mounting Type: Surface Mount
• Package / Case: 64-LFCSP
• Adc/dac Resolution: 9b
• Screening Level: Industrial
• Package Type: LFCSP EP
• Pin Count: 64
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With: EVAL-ADV7181BEB - BOARD EVALUATION FOR ADV7181
• Lead Free Status / RoHS Status: Compliant, Contains lead / RoHS non-compliant

Letterbox Detection
Incoming video signals may conform to different aspect ratios
(16:9 wide screen of 4:3 standard). For certain transmissions in
the wide screen format, a digital sequence (WSS) is transmitted
with the video signal. If a WSS sequence is provided, the aspect
ratio of the video can be derived from the digitally decoded bits
WSS contains.
In the absence of a WSS sequence, letterbox detection can be
used to find wide screen signals. The detection algorithm exam-
ines the active video content of lines at the start and end of a
field. The detection of black lines can indicate that the
currently shown picture is in wide screen format.
The active video content (luminance magnitude) over a line of
video is summed together. At the end of a line, this accumulated
value is compared with a threshold, and a decision is made as to
whether or not a particular line is black. The threshold value
needed may depend on the type of input signal; some control is
provided via LB_TH[4:0].
Detection at the Start of a Field
The ADV7181 expects a section of at least six consecutive black
lines of video at the top of a field. Once those lines have been
detected, Register LB_LCT[7:0] reports back the number of
black lines that were actually found. By default, the ADV7181
starts looking for those black lines in sync with the beginning of
active video, for example, straight after the last VBI video line.
LB_SL[3:0] allows the user to set the start of letterbox detection
from the beginning of a frame on a line-by-line basis. The
detection window closes in the middle of the field.
Detection at the End of a Field
The ADV7181 expects at least six continuous lines of black
video at the bottom of a field before reporting back the number
of lines actually found via the LB_LCB[7:0] value. The activity
window for letterbox detection (end of field) starts in the mid-
dle of an active field. Its end is programmable via LB_EL[3:0].
Detection at the Midrange
Some transmissions of wide screen video include subtitles
within the lower black box. If the ADV7181 finds at least two
black lines followed by some more nonblack video, for example,
the subtitle, and finally followed by the remainder of the bottom
black block, it reports back a midcount via LB_LCM[7:0].
When no subtitles are found, LB_LCM[7:0] reports the same
number as LB_LCB[7:0].
Notes
•
•
There is a 2-field delay in the reporting of any line count
parameters.
There is no “letterbox detected” bit. The user is asked to
read the LB_LCT[7:0] and LB_LCB[7:0] register values and
Rev. B | Page 53 of 104
LB_LCT[7:0] Letterbox Line Count Top, Address 0x9B [7:0];
LB_LCM[7:0] Letterbox Line Count Mid, Address 0x9C [7:0];
LB_LCB[7:0] Letterbox Line Count Bottom,
Address 0x9D [7:0]
Table 145. LB_LCx Access Information
Signal Name
LB_LCT[7:0]
LB_LCM[7:0]
LB_LCB[7:0]
LB_TH[4:0] Letterbox Threshold Control, Address 0xDC [4:0]
Table 146. LB_TH Function
LB_TH[4:0]
01100 (default)
01101 to 10000
00000 to 01011
LB_SL[3:0] Letterbox Start Line, Address 0xDD [7:4]
Table 147. LB_SL Function
LB_SL[3:0]
0100 (default)
0001, 0010
LB_EL[3:0] Letterbox End Line, Address 0xDD [3:0]
Table 148. LB_EL Function
LB_EL[3:0]
1101 (default)
0001,0010
Gemstar Data Recovery
The Gemstar-compatible data recovery block (GSCD) supports
1× and 2× data transmissions. In addition, it can also serve as a
closed caption decoder. Gemstar-compatible data transmissions
can only occur in NTSC. Closed caption data can be decoded in
both PAL and NTSC.
The block is configured via I
•
•
to come to a conclusion about the presence of letterbox
type video in software.
GDECEL[15:0] allow data recovery on selected video lines
on even fields to be enabled and disabled.
GDECOL[15:0] enable the data recovery on selected lines
for odd fields.
Address
0x9B
0x9C
0x9D
Description
Default threshold for detection of black lines.
Increase threshold (need larger active video
content before identifying non-black lines).
Decrease threshold (even small noise levels
can cause the detection of non-black lines).
Description
Letterbox detection is aligned with active
video. Window starts after the EDTV VBI data
line. For example, 0100 = 23/286 (NTSC).
For example, 0101 = 24/287 (NTSC).
Description
Letterbox detection ends with the last active
line of video on a field. For example, 1101 =
262/ 525 (NTSC).
For example, 1100 = 261/524 (NTSC).
2
C in the following way:
Register Default Value
Readback only
Readback only
Readback only
ADV7181