AK8851 Datasheet, PDF (44/80 Pages) Asahi Kasei Microsystems – NTSC/PAL/SECAM Digital Video Decoder

ASAHI KASEI
26. Output Interface
(1) ITU-R BT.656 Interface
The AK8851 outputs decoded data in ITU-R BT.656 compatible interface format.
ITU-R BT.656 compatible output data means:
* Samples per Line: 858 samples (525 system)/864 samples (625 system)
* Line numbers per Frame : 525 Lines / 625 Lines
[AK8851]
The above output cannot be obtained when the input signal quality is poor (if using the fixed clock mode, and a good
input signal, the above specification may not be met).
In the AK8851, the PLL is locked to the input signal and buffers on the output stage absorb input signal jitter, which
assures ITU-R BT.656 compatible output.
However when the input signal jitter is very large and exceeds the allowable range of the output buffer, ITU-R BT.656
output cannot be met. In this case, one of the following output modes is set via registers.
(1-1) Guarantee of 858 samples:
Number of samples per Line is guaranteed to be 858 or 864.
When ITU-R BT.656 is not met, Line-drop or Line-repeat processing is performed. This means that the number of Lines
per Frame is not necessarily 525 or 625 (524 or 624 Lines for Line-drop cases. 526 or 626 Lines at Line-repeat cases).
The above Line-drop or Line-repeat processing can take place at any arbitrary Lines of each Frame.
(1-2) Guarantee of 525 / 625 Lines :
Number of Lines per Frame is guaranteed to be 525 or 625. In this mode, Pixel-drop or Pixel-repeat processing is
performed at the last Line of each Field/Frame. This means that the number of samples per Line is not always 858 or 864
(the output buffer is cleared at the last Line of either each Frame or each Field so that the remaining size of the output
buffer is set to its maximum value).
Field or Frame selection of this processing is set by register.
ITU-R BT.656 interface process-related register is [ERRHND1 ERRHND0]-bit of [Control 2 Register][Sub Address 0x09].
Sub Address 0x09
bit 7
bit 6
Reserved
Reserved
0
0
bit 5
ERRHND1
0
bit 4
bit 3
ERRHND0 NOSIGDET
Default Value
0
0
bit 2
BLUEBACK
0
Default Value : 0x00
bit 1
bit 0
DPAL1
DPAL0
0
0
[ERRHND1:ERRHND0]-bit
[ERRHND1:ERRHND0]-bit
00
01
10
11
Function
Line drop/repeat is done
The number of sample is 858/864.
Depending of the input video signal quality, the number of Lines for
output data is not 525/625 lines.
Pixel drop/repeat is done.
Pixel drop/repeat is done at line in the end of frame. The number of
lines in the frame is 525/625.
Depending of the input video signal quality, the number of samples in
the last of line in field is not 858/864 samples.
Pixel drop/repeat is done.
Pixel drop/repeat is done at line in the end of frame. The number of
lines in the frame is 525/625.
Depending of the input video signal quality, the number of samples in
the last of line in frame is not 858/864 samples.
Reserved
Note
Default
MS0244-E-03
44
Confidential
2005 / 07