bt848kpf ETC-unknow, bt848kpf Datasheet - Page 41

• Manufacturer Part Number: bt848kpf
• Description: Single-chip Video Capture For Pci
• Manufacturer: ETC-unknow

Bt848/848A/849A
Single-Chip Video Capture for PCI
Brooktree
Temporal Decimation
®
Figure 16. Regions of the Video Signal
tween the rising edge of VRESET and the start of active video lines. It determines
how many lines to skip before initiating the ACTIVE signal. It is programmed with
the number of lines to skip at the beginning of a frame.
lines used in the vertical scaling process. The actual number of vertical lines output
from the Bt848 is equal to this register times the vertical scaling ratio. If VSCALE
is set to 0x1A00 (4:1) then the actual number of lines output is VACTIVE/4. If VS-
CALE is set to 0x0000 (1:1) then VACTIVE contains the actual number of vertical
lines output.
horizontal registers (HSCALE, HDELAY, and HACTIVE) and the vertical regis-
ters (VSCALE, VDELAY, and VACTIVE). Horizontally, HDELAY and HAC-
TIVE are programmed with respect to the scaled pixels defined by HSCALE.
Vertically, VDELAY and VACTIVE are programmed with respect to the number of
lines before scaling (before VSCALE is applied).
Temporal decimation provides a solution for video synchronization during periods
when full frame rate can not be supported due to bandwidth and system restric-
tions.
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 Bt848’s time
scaling operation will enable the system to capture every other frame instead of al-
lowing 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 avail-
able.
temporal decimation register (TDEC) 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 remain-
ing low.
The Vertical Delay Register (VDELAY) is programmed with the delay be-
The Vertical Active Register (VACTIVE) is programmed with the number of
Note: It is important to note the difference between the implementation of the
For example, when capturing live video for storage, system limitations such as
The Bt848 provides temporal decimation on either a field or frame basis. The
HDELAY
L848A_A
Porch
Front
Video Scaling, Cropping, and Temporal Decimation
HACTIVE
F
UNCTIONAL
D
ESCRIPTION
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