Transition from Traditional NI-DAQ (Legacy) to NI-DAQmx in LabVIEW

NI recommends starting with a new VI and using the old VIs written in Traditional NI-DAQ (Legacy) as a guide. Although many of the programming techniques are similar, there are some slight differences that will be pointed out in this document. Please note that this article is intended to be a supplement to the other help documents available, not a substitution. After you understand what is described in this article, you should have a clear idea of the main differences to keep in mind when programming in NI-DAQmx.

Since it is recommended to start code from scratch, here are a few guidelines and suggestions to make that transition as easy as possible. A helpful tool available since LabVIEW 7.0 and later is the DAQ Assistant. With this assistant, you can designate what you want your code to do in Measurement & Automation Explorer (MAX), and then generate code based on that task.  After generating the code, you can then edit it by adding property nodes or changing the configuration to meet the needs of your specific application. If you would like more information on how the DAQ Assistant works, refer to Taking an NI-DAQmx Measurement in LabVIEW.

One major difference between the two drivers is in the palettes. In Traditional NI-DAQ (Legacy), there is a different palette for each type of operation, such as a digital palette for digital operations, an analog input palette for all analog input operations, and so on. In NI-DAQmx, just one set of VIs is used for all operations, and you can configure each VI for a specific type of acquisition. For example, in Traditional NI-DAQ (Legacy), you use the AI Config.vi to configure a channel or set of channels for analog input. In NI-DAQmx, you use the DAQmx Create Channel.vi, and configure this VI for Analog Input: Voltage. This distinction makes it easier to become familiar with the specific VIs needed to perform various operations. 

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Figure 1. Traditional NI-DAQ (Legacy): Cont Acq&Graph (buffered).vi


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Figure 2. NI-DAQmx: Cont. Acq&Graph Voltage-Int Clk.vi

This example shows the difference between Traditional NI-DAQ (Legacy) and NI-DAQmx when performing continuous analog input with an internal clock. To translate a program written with Traditional NI-DAQ (Legacy) into NI-DAQmx, follow these steps:

1. First, replace the AI Config.vi with the DAQmx Create Channel.vi.
2. Configure the DAQmx Create Channel.vi for Voltage by selecting from the dropdown below the VI Analog Input>>Voltage. This information needs to be set because the DAQmx Create Channel.vi is a polymorphic VI used for all types of acquisition. This is unlike Traditional NI-DAQ (Legacy) where different VIs are used for the different types of acquisitions.
3. Create the controls on the front panel so that the data types correlate. Notice that there are no longer device number and channel name controls because they are combined into one control denoted by the Physical Channel. Another configurable input on this VI is the Input Terminal Configuration. The board automatically defaults to Differential mode. The referencing mode is no longer set in MAX, to measure in NRSE or RSE, you must specify it here.
4. Now insert the DAQmx Timing.vi after the DAQmx Create Channel.vi. The DAQmx Timing.vi sets the sample rate and creates the buffer for continuous acquisition. Since continuous acquisition is specified, LabVIEW automatically creates a buffer to make use of buffered acquisition.
5. Replace the AI Start.vi with the DAQmx Start Task.vi, which is similar in functionality. The most significant difference between the two is that the sample rate is no longer set when you start the acquisition, but instead set with the DAQmx Timing.vi.
6. Replace the AI Read.vi with the DAQmx Read.vi.
7. Configure the DAQmx Read.vi for Analog»Multiple Channels»Multiple Samples»1D Waveform.
8. Create the constants, controls, and indicators so they are connected to the correct terminals.
9. Replace the AI Clear.vi with the DAQmx Clear Task.vi. The inputs to this VI are the same and it performs the same function.

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Figure 3. Traditional NI-DAQ (Legacy): Continuous Generation IntClk.vi

This example shows the difference between Continuous Analog Output in Traditional NI-DAQ (Legacy) and NI-DAQmx. To convert a program written in Traditional NI-DAQ (Legacy) to NI-DAQmx, follow these steps:

1. First, replace the AO Config.vi with the DAQmx Create Channel.vi.
2. Create all the controls so that the data types match. In NI-DAQmx, the Physical Channel input specifies the device number as well as the channel number, instead of the two separate controls required in Traditional NI-DAQ (Legacy).
3. Replace the Compute Waveform.vi with a very similar VI called Waveform Buffer Generation.vi. This new VI passes the task through the waveform generation VI, as opposed to having to wire around it as in Traditional NI-DAQ (Legacy).
4. Replace the AO Write.vi with both the DAQmx Timing.vi and the DAQmx Write.vi.
5. Configure the DAQmx Timing.vi for the Sample Clock. The DAQmx Timing.vi, when configured for the Sample Clock, specifies the sample mode as well as the clock source to use.
6. Set the DAQmx Write.vi to use Analog»Single Channel»Multiple Sample»Waveform.
7. Create the necessary inputs and make sure the data types are equivalent.
8. Replace the AO Start.vi with the DAQmx Start Task.vi. Both of these VIs have similar inputs and outputs and generally perform the same functions.
9. Inside the while loop, substitute the AO Write.vi with the DAQmx Is Task Done.vi. Because this example uses continuous generation, you do not necessarily need to use the DAQmx Is Task Done.vi because the task will not be complete until you press the stop button on the front panel. However, if you are performing a finite generation, this VI is essential to signify the end of the operation.
10. Replace the AO Clear.vi with the DAQmx Clear Task.vi. Both of these VIs achieve the same function.

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Figure 5. Traditional NI-DAQ (Legacy): Write to 1 Dig Port.vi

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Figure 6. NI-DAQmx: Write Dig Port.vi

The example above illustrates the difference between doing Digital Port Writes in Traditional NI-DAQ (Legacy) and in NI-DAQmx. To move a Traditional NI-DAQ (Legacy) program to NI-DAQmx, follow these steps:

1. First, replace the DIO Port Config.vi with both the DAQmx Create Channel.vi and the DAQmx Start Task.vi.
2. Configure the DAQmx Create Channel.vi for Digital Output.
3. Create controls and make sure the data types of the controls match up correctly.
4. When creating the port control, specify the entire port and not just a specific line number.
5. Now substitute everything inside the while loop except the Wait function and the stop button with the DAQmx Write.vi.
6. Configure the DAQmx Write.vi for Digital»Single Channel»Single Sample»U8 (Port Format). This VI takes care of writing all the data.
7. Add a DAQmx Clear Task.vi outside the while loop to clear the task created for the program.

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Figure 7. Traditional NI-DAQ (Legacy): Generate Pulse Train (DAQ-STC).vi

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Figure 8. NI-DAQmx: Gen Dig Pulse Train-Continuous-Pause Trigger.vi

This example demonstrates the difference between doing Continuous Pulse Train Generation in Traditional NI-DAQ (Legacy) and NI-DAQmx. Follow these steps to transition a program written in Traditional NI-DAQ (Legacy) to NI-DAQmx.

1. First, replace the Counter Group Config.vi with the DAQmx Create Channel.vi.
2. Configure the DAQmx Create Channel.vi for Counter Output»Pulse Generation»Frequency.
3. Create separate controls for the Duty Cycle, Frequency, Counter, and Idle State. The Counter control specifies which device as well as which counter to use. The Idle State input informs the counter in which state to start and to which state to return after the pulse train has completed. The Set Pulse Specs.vi is no longer needed because those values are set on the DAQmx Create Channel.vi instead.
4. Replace the Counter Gate (STC).vi with a DAQmx Trigger property node. Set the Trigger Type to Digital Level in the property node, and then create a control on the front panel to select the source of the gate.
5. Insert the DAQmx Timing.vi after the DAQmx Trigger property node. The DAQmx Timing.vi is configured to Implicit (Counter). This VI indicates the duration of the pulse generation.
6. Add a DAQmx Timing property node after the DAQmx Timing.vi. In this case, the timing property node specifies the onboard clock and configures an external clock, if desired. This is used in lieu of the case structure in the Traditional NI-DAQ (Legacy) example.
7. Replace the Counter Control.vi with a DAQmx Is Task Done.vi inside the while loop. The purpose of this VI is to check when finite generation is finished. For this example, the DAQmx Is Task Done.vi can be omitted since it is continuous, but if performing finite generation, you need to include this VI.
8. Replace the Counter Control.vi with the DAQmx Clear Task.vi. The inputs to this new VI are very similar, except that the task automatically resets without specifying to do so.

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Figure 9. Traditional NI-DAQ (Legacy): Share 653x REQ Clock with E Series AI Sample Clock.vi

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Figure 10. NI-DAQmx: Share 653x REQ Clock with E Series AI Sample Clock.vi

This example illustrates how to synchronize a 653X board with an E Series board. The REQ clock of the 653X is used as the sample clock for an analog input acquisition on the E Series board. This is shown above using Traditional NI-DAQ (Legacy) as well as NI-DAQmx. The example demonstrates the flexibility and the interoperability of the two drivers, and how much clearer RTSI use is in NI-DAQmx. The digital board portion on both examples uses the Traditional NI-DAQ (Legacy) driver, so this explanation describes only how to convert the segment of code running on the E Series board.

1. First, replace the AI Config.vi with theDAQmx Create Channel.vi.
2. Configure the DAQmx Create Channel.vi for Voltage by selecting from the dropdown below the VI Analog Input»Voltage.
3. Create the controls on the front panel and the necessary constants.
4. Replace the AI Clock Config.vi with the DAQmx Timing.vi. The DAQmx Timing.vi sets the sample rate and creates the buffer, because continuous acquisition is desired. The buffer is acquired automatically since it is set up for continuous acquisition. One important input to this VI is the Source. Leave the input blank if you want to use the default onboard clock. For this example, however, create a constant and set it to use the RTSI pin that is routed from the digital board (which in this case is /Dev4/RTSI0). Notice that this name permits you to specify a different device number. This is important because NI-DAQmx accomplishes all the internal routing for you.
5. Replace the AI Control.vi with the DAQmx Start Task.vi, which is similar in functionality.
6. Replace the AI Read.vi with the DAQmx Read.vi.
7. Configured the DAQmx Read.vi for Analog»Single Channel»Multiple Samples»1D Waveform. You must provide this information because the DAQmx Read.vi is a polymorphic VI used for all types of data acquisition (as opposed to Traditional NI-DAQ (Legacy), where there are many unique VIs for different types of acquisition).
8. Replace the AI Clear.vi with the DAQmx Clear Task.vi. The inputs to this VI are the same and they perform the same functionality.

• Getting Started with DAQmx: Basic of DAQmx Property Nodes
• Sampling Terminology for NI-DAQmx and Traditional NI-DAQ (Legacy)
• Product Documentation: Traditional NI-DAQ User Manual (Archived)
• Product Documentation: NI-DAQmx Installed Documentation
• Transitioning from Traditional NI-DAQ (Legacy) to NI-DAQmx Using ANSI C and NI LabWindows™/CVI