Chapter 2
Hardware Overview
2-8
ni.com
Scatter-Gather DMA Controllers
The NI 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 NI 1426 can perform continuous image
transfers directly to either contiguous or fragmented memory buffers.
Bus Master PCI Interface
The NI 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 NI 1426 can start acquisitions in the following ways:
•
Software control
—The NI 1426 supports software control of a start
acquisition. You can configure the NI 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.
•
Delayed acquisition
—Use either software or triggers to start
acquisitions instantaneously or after skipping a specific number of
frames. You can use delayed acquisition for post-trigger applications.
