Chapter 2
Hardware Overview
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National Instruments Corporation
2-7
High-Speed Timing
Built from high-speed counters, the high-speed timing circuitry on the
NI 1426 can generate precise real-time control signals for your camera.
Map the output of this circuitry to a trigger line to provide accurate pulses
and pulse trains. Map these control signals to the camera control lines to
control exposure time and frame rate.
Note
For your convenience, the external control for cameras that support the NI 1426 has
been preprogrammed into the camera file. You can use MAX to specify the frequency and
duration of these signals in easy-to-use units.
The NI 1426 also allows you to route the external trigger inputs 0–3 onto
the camera control lines 1–4. Use MAX to select the source for the camera
control lines. You have the option to choose either the default control signal
that is specified in the camera file or the external trigger input as the source
for the camera control lines.
Acquisition and Region of Interest (ROI)
The acquisition and ROI circuitry monitors incoming video signals and
routes the active pixels to the multiple-tap data formatter and SDRAM.
The NI 1426 can perform ROI acquisitions on all video lines and frames.
In an ROI acquisition, select an area within the acquisition window to
transfer across the PCI bus to system memory.
Configure the following parameters on the NI 1426 to control the video
acquisition window:
•
Acquisition window
—The NI 1426 allows the user to specify a
particular region of active pixels and active lines within the incoming
video data. The active pixel region selects the starting pixel and
number of pixels to be acquired relative to the assertion edge of the
horizontal (or line) enable signal from the camera. The active line
region selects the starting line and number of lines to be acquired
relative to the assertion edge of the vertical (or frame) enable signal.
•
Region of interest
—
The NI 1426 uses a second level of active pixel
and active line regions for selecting a region of interest. Using the
region-of-interest circuitry, the device acquires only a selected subset
of the acquisition window.
Note
You can use MAX to set the acquisition window on the NI 1426.
