Chapter 3
Hardware Overview
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National Instruments Corporation
3-7
Configure the following parameters on the IMAQ 1426 to control the video
acquisition window:
•
Acquisition window—The IMAQ 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 IMAQ 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 IMAQ 1426.
Scatter-Gather DMA Controllers
The IMAQ 1426 uses three independent onboard direct memory access
(DMA) controllers. The DMA controllers transfer data between the
onboard SDRAM memory buffers and the PCI bus. Each of these
controllers supports scatter-gather DMA, which allows the DMA controller
to reconfigure on-the-fly. The IMAQ 1426 can perform continuous image
transfers directly to either contiguous or fragmented memory buffers.
Bus Master PCI Interface
The IMAQ 1426 implements the PCI interface with a National Instruments
custom application-specific integrated circuit (ASIC), the PCI miniMITE.
The PCI interface can transfer data at a theoretical maximum rate of
133 MB/s in bus master mode.
Start Conditions
The IMAQ 1426 can start acquisitions in the following ways:
•
Software control—The IMAQ 1426 supports software control of a
start acquisition. You can configure the IMAQ 1426 to capture a fixed
number of frames. This configuration is useful for capturing a single
frame or a sequence of frames.
•
Trigger control—You can start an acquisition by enabling external
or RTSI bus trigger lines. Each of these inputs can start a video
acquisition on a rising or falling edge. You can use all four external
triggers and up to four RTSI bus triggers simultaneously.
