Use the I/O controls on the I/O and Classic I/O palettes to specify the instrument or device resource you want to communicate with. Use the VIs on the Measurement I/O palette to develop DAQ applications.

Complete the following basic programmatic steps to create a DAQ application.

1. Configure the measurement hardware.
2. Create tasks and channels.
3. (Optional) Set timing.
4. (Optional) Set triggering.
5. Read or write data.
6. Clear.

Notice that timing and triggering are optional. Include the timing step if you want to specify hardware timing instead of software timing. If you are using NI-DAQmx, you can use the DAQ Assistant to set timing parameters for a task.

Use triggering if you want the device to acquire samples only when certain conditions are met. For example, you might want to acquire samples if the input signal goes higher than 4 V. If you are using NI-DAQmx, you can use the DAQ Assistant to configure triggering for a task.

Many NI-DAQmx applications also can include steps to start, stop, and clear the task. For example, for applications that use a counter/timer to count edges or to measure period, use the Start VI to arm the counter.

In NI-DAQmx, LabVIEW clears the task automatically when the VI hierarchy that created the task finishes executing.

Traditional NI-DAQ (Legacy) and NI-DAQmx include VIs for timing, triggering, reading, and writing samples. Use the Data Acquisition VIs and Functions to acquire data from DAQ devices. To use these VIs, you must have the NI-DAQ driver software and DAQ hardware installed. After you acquire data, you can use the built-in Signal Processing, Report Generation, and Mathematics VIs and functions to analyze, generate reports, and perform mathematical operations on that data.

You can use the NI-DAQmx properties to extend the functionality of the NI-DAQmx VIs.

Many of the Traditional NI-DAQ (Legacy) and NI-DAQmx VIs are polymorphic and can accept or return data of various types, such as scalar values, arrays, or waveforms. You use other polymorphic NI-DAQmx VIs to configure various triggers and methods of sample timing, and to create virtual channels. By default, NI-DAQmx VIs appear with the polymorphic VI selector.

Physical and Virtual Channels

A physical channel is a terminal or pin at which you can measure or generate an analog or digital signal. Every physical channel on a device that supports NI-DAQmx has a unique name.

A virtual channel is a collection of property settings that can include a name, a physical channel, input terminal connections, the type of measurement or generation, and scaling information. In Traditional NI-DAQ (Legacy) and earlier versions, configuring virtual channels is an optional way to record which channels are being used for different measurements, but virtual channels are integral to every NI-DAQmx measurement.

Tasks

A task in NI-DAQmx is a collection of one or more virtual channels with timing, triggering, and other properties. A task represents a measurement or a generation you want to perform. You can set up and save all of the configuration information in a task and use the task in an application.

In NI-DAQmx, you can configure virtual channels as part of a task or separate from a task.

Complete the following steps to perform a measurement or a generation with a task.

1. Create a task and channels.
2. (Optional) Configure the channel, timing, and triggering properties.
3. Read or write samples.
4. Clear the task.

Repeat steps 2 and 3, if it is appropriate for the application. For example, after reading or writing samples, you can reconfigure the channel, timing, or triggering properties and then read or write additional samples based on this new configuration.