Chapter 3
Hardware Overview
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National Instruments Corporation
3-5
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Delayed acquisition—You can use either software or the trigger to start
and stop acquisitions instantaneously or after capturing a desired
number of frames or fields. Use this feature for trigger applications.
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Frame/field selection—With an interlaced camera and the
PCI/PXI-1407 in frame mode, you can program the PCI/PXI-1407
to start acquisition on any odd field or any even field.
Acquisition Window Control
You can configure numerous parameters on the PCI/PXI-1407 to
control the video acquisition window. A brief description of each
parameter follows:
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Active pixel region—The active pixel region is the region of pixels
actively being stored. The active pixel region is defined by a pixel start
(relative to HSYNC) and a pixel count.
•
Horizontal count—The horizontal count is the total number of pixels
between two HSYNC signals. The horizontal count determines the
frequency of the pixel clock.
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Active line region—The active line region is the region of lines
actively being stored. The active line region is defined by a line
start (relative to VSYNC) and a line count.
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Line count—The line count is the total number of horizontal lines
in the picture.
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Video line—A video line consists of an HSYNC, back porch, active
pixel region, and a front porch. The 1407 device requires a positive
video signal, as shown in Figure 3-2.
Figure 3-2.
Positive Video Line
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Picture aspect ratio—The picture aspect ratio is the ratio of the active
pixel region to the active line region. For standard video signals like
RS-170 or CCIR, the full-size picture aspect ratio normally is
4/3 (1.33).
Horizontal Sync
Pixel Region
Back Porch
Front Porch
