National Instruments Eight-slot USB Chassis NI cDAQ-9172 - Manual (Page 39)

© National Instruments Corporation 39 NI cDAQ-9172 User Guide and Specifications
Change Detection Event
The Change Detection Event is the signal generated when a change on the
rising or falling edge lines is detected by the change detection task.
Routing Change Detection Event to an Output
Terminal
You can route ChangeDetectionEvent to any output PFI terminal.
Change Detection Acquisition
You can configure lines on correlated digital modules in slots 1 through 4
to detect rising or falling edges. When one or more of these lines sees the
edge specified for that line, the NI cDAQ-9172 chassis samples all the lines
in the task. The rising and falling edge lines do not necessarily have to be
in the task.
Change detection acquisitions can be buffered or nonbuffered:
• Nonbuffered Change Detection Acquisition—In nonbuffered
acquisitions, correlated digital input modules in any slot may be in the
task, but the rising/falling edge detection lines must be in slots 1
through 4.
• Buffered Change Detection Acquisition—A buffer is a temporary
storage in computer memory for acquired samples. In a buffered
acquisition, data is stored in the NI cDAQ-9172 onboard FIFO then
transferred to a PC buffer. Buffered acquisitions typically allow for
much faster transfer rates than nonbuffered acquisitions because data
accumulates and is transferred in blocks, rather than one sample at a
time. With buffered acquisitions, all modules in the task must be in
slots 1 through 4.
Digital Input/Output Configuration for NI 9401
When you change the configuration of lines on a NI 9401 digital I/O
module between input and output, NI-DAQmx temporarily reserves all
of the lines on the module for communication to send the module a line
configuration command. If another task or route is actively using the
module, to avoid interfering with the other task, NI-DAQmx generates an
error instead of sending the line configuration command. During the line
configuration command, the output lines are maintained without glitching.