Chapter 2
Hardware Overview
©
National Instruments Corporation
2-9
NI PCIe-1427 User Manual
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. The NI 1427 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 host bus to system memory. If the area of the image you need is smaller
than the camera output that appears in the acquisition window, select an
ROI to speed up the transfer and processing times for the image.
Note
You can use MAX to set the acquisition window on the NI 1427.
Acquisition Window Control
You can configure the following parameters on the NI 1427 to control the
video acquisition window:
•
Acquisition window
—The NI 1427 allows you 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 1427 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.
DMA Controllers
The NI 1427 uses onboard direct memory access (DMA) controllers to
transfer data between the device and host memory. Each of these controllers
supports scatter-gather DMA, which allows the DMA controller to
reconfigure at run time. The NI 1427 can perform continuous image
transfers directly to either contiguous or fragmented memory buffers. The
NI-IMAQ driver software efficiently programs the DMA engines while
providing an easy-to-use high-level interface.
PCIe Interface
The NI 1427 is compliant with the PCI Express 1.1 specification. The
NI 1427 is intended for a x1 PCIe slot. The NI 1427 fits into, and can also
be used in, a x4, x8, or x16 PCIe slot. Using a smaller width device in a
larger width slot is called up-plugging.
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