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#2 AO 16 DIO 2 COUNTER 1 TRIGGER HOW TO#Once the trigger signal is received, a specified number of points before and after the trigger are returned to the calling application (e.g., LabVIEW, C++, etc.) by the driver.įigure 8 illustrates how to create a pretriggered application in LabVIEW by specifying the desired number of pretrigger samples in the DAQmx Reference Trigger VI. NI-DAQmx stores the digitized data in computer memory in a circular buffering scheme, replacing the oldest points in the buffer with the new samples. #2 AO 16 DIO 2 COUNTER 1 TRIGGER SOFTWARE#In a pretriggered acquisition, the A/D conversions are initiated with a software function call. Pretriggered Acquisition on a Digital Reference Trigger The default trigger source is PFI0, but an alternate trigger source (e.g., another PFI line or RTSI line) can be selected by setting the Source of the DAQmx Trigger VI.ī. The NI E and M Series multifunction I/O devices provide the added flexibility to choose from one of the several PFI lines on the board as the trigger input. If the triggering edge is defined as Rising, then the analog input task will begin as soon as a rising edge occurs on the specified digital line. ![]() In this example, the Analog Input task will wait until it sees the digital trigger. ![]() #2 AO 16 DIO 2 COUNTER 1 TRIGGER CODE#The following code shows how to set up a posttriggered application using NI-DAQmx functions:įigure 7: Posttriggered Acquisition with a Digital Trigger The digital trigger is typically wired to the external trigger input of the I/O connector of the specified device. In a posttriggered acquisition, the A/D conversions start after the DAQ hardware receives the trigger signal. Posttriggered Acquisition with a Digital Start Trigger The rest of this document discusses how to implement various triggering types using LabVIEW and NI-DAQmx functions. In addition, more complicated triggering tasks can be implemented using the DAQmx Trigger Property Node. You can use this VI to specify the source of the trigger and the desired edge to trigger on. The DAQmx Digital Trigger VI shown below can be used to configure a digital triggering task. Trigger conditions for any application are specified in the configuration section by calling the appropriate NI-DAQmx functions or VIs in LabVIEW. ![]() NI-DAQmx applications typically consist of the four building blocks shown below (Figure 5).įigure 5: Flowchart for a Typical DAQmx Application In this case, you would simply make function calls from the NI-DAQmx API. Alternatively, you could use the same design process to program a triggering application in a text-based programming environment. #2 AO 16 DIO 2 COUNTER 1 TRIGGER DRIVER#This section serves as a guideline for developing triggered applications using the NI-DAQmx driver in LabVIEW. ![]() The trigger signal in this case is referred to as the reference trigger. The primary responsibility of the trigger mechanism is to stop the acquisition so that the samples left in memory represent the “slice-in-time” the user wants. When the buffer is full, it simply wraps around and stores each subsequent sample over the oldest sample in memory. The buffer is large enough to ensure that the required number of pretrigger samples are stored. In such applications, the hardware initiates data acquisition with a software function and stores the data in a circular buffer in the PC memory. With this type of acquisition, the user can view the signal before the trigger event. In a pretriggered acquisition, the hardware starts acquiring data before the trigger signal is received (Figure 4). The trigger signal in this case is referred to as the start trigger.įigure 3: Posttriggered Acquisition Pretriggered Acquisition In a posttriggered acquisition, the hardware starts the A/D conversions after the trigger is received (Figure 3). Triggered data acquisition applications can be classified in two ways: posttriggered and pretriggered. ![]()
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