bt829bkrf ETC-unknow, bt829bkrf Datasheet - Page 42

• Manufacturer Part Number: bt829bkrf
• Description: Video Streamii Decoders
• Manufacturer: ETC-unknow

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1.0 Functional Description
1.7 Video Scaling, Cropping, and Temporal Decimation
1.7.8 Temporal Decimation
Temporal decimation provides a solution for video synchronization during peri-
ods when full frame rate cannot be supported due to bandwidth and system
restrictions.
hard disk transfer rates or system bus bandwidth may limit the frame capture rate.
If these restrictions limit the frame rate to 15 frames per second, the Bt829B’s
time scaling operation will enable the system to capture every other frame instead
of allowing the hard disk timing restrictions to dictate which frame to capture.
This maintains an even distribution of captured frames and alleviates the “jerky”
effects caused by systems that simply burst in data when the bandwidth becomes
available.
The Temporal Decimation TDEC register is loaded with a value from 1 to 60
(NTSC) or 1 to 50 (PAL/SECAM). This value is the number of fields or frames
skipped by the chip during a sequence of 60 for NTSC or 50 for PAL/SECAM.
Skipped fields and frames are considered inactive, which is indicated by the
ACTIVE pin remaining low. Consequently if QCLK is programmed to depend on
ACTIVE, QCLK would become inactive as well.
should be loaded first, and then the decimation value. This will ensure that the
decimation counter is reset to zero. If zero is not first loaded, the decimation may
start on any field or frame in the sequence of 60 (or 50 for PAL/SECAM). On
power-up, this preload is not necessary because the counter is reset internally.
grammed to choose whether the decimation starts with an odd field or an even
field. If the FLDALIGN bit is set to logical 0, the first field that is dropped during
the decimation process will be an odd field. Conversely, setting the FLDALIGN
bit to logical 1 causes the even field to be dropped first in the decimation process.
For example, when capturing live video for storage, system limitations such as
The Bt829B provides temporal decimation on either a field or frame basis.
Examples:
When changing the programming in the temporal decimation register, 0x00
When decimating fields, the FLDALIGN bit in the TDEC register can be pro-
TDEC = 0x02
TDEC = 0x9E
TDEC = 0x01
TDEC = 0x00
D829BDSA
Decimation is performed by frames. Two frames are
skipped per 60 frames of video, assuming NTSC
decoding.
mains low for one frame. Frames 30–59 are then output
followed by another frame of inactive video.
Decimation is performed by fields. Thirty fields are
output per 60 fields of video, assuming NTSC
decoding.
of video starting with Field 1 in Frame 1.
Decimation is performed by frames. One frame is
skipped per 50 frames of video, assuming
PAL/SECAM decoding.
Decimation is not performed. Full frame rate video is
output by the Bt829B.
Frames 1–29 are output normally, then ACTIVE re-
This value outputs every other field (every odd field)
VideoStream II Decoders
Bt829B/827B