Data Formats in NI-DAQmx
Data format deals with the type of the data that is read or written.
Analog Channel Data Formats
Waveform
The waveform data format includes the channel name, timing, and unit information with the actual 64-bit scaled floating-point data. Your ADE provides a mechanism for extracting and setting individual parts of the waveform.
For input tasks, you can use the additional information for a variety of purposes. For example, you can update graphs to show the timing information and include labels with the channel names. Analysis routines can use the timing information for calculations such as FFTs. Because there is overhead associated with including this additional information, NI-DAQmx allows you to configure the information you want to include.
For output tasks, the timing information is the primary field that is useful. A library that generates a waveform can include timing information that sets up the timing for your output task.
When reading data, the waveform data includes the time when the first sample in the waveform was acquired, t0, and the amount of time that elapsed between each sample, dt. However, there are limitations on these two values.
64-Bit Floating-Point Numbers
The 64-bit floating-point number format allows you to read or write scaled data with no additional information. Use this format to work with scaled data that requires higher performance than the waveform format provides. You might also use this format because it is a better match for the libraries you plan to use.
Unsigned and Signed Integers
The unsigned and signed integer format reads or writes data in the native format of the device. Use this format for maximum performance. The tradeoff is that your application has to understand how to interpret and manipulate data that is not in engineering units.
Digital Channel Data Formats
Waveform
The waveform data format includes the channel name and timing information with the actual data represented in a dedicated digital format. Your ADE provides a mechanism for extracting and setting individual parts of the waveform.
The dedicated digital format represents digital data similar to logic analyzers and digital simulation tools. Each channel has no limits on the number of lines. In addition, the digital format allows for additional states beyond basic 1s and 0s. The ADE can take advantage of this format by tailoring data and graph displays for the digital data.
For input tasks, you can use the additional information for a variety of purposes. For example, you can update graphs to show the timing information and include labels with the channel names. Because there is overhead associated with including this additional information, NI-DAQmx allows you to configure the information you want to include.
For output tasks, the timing information is the primary field that is useful. A waveform generated by a library may include timing information that you can use to set up the timing for your output task.
When reading data, the waveform data includes the time when the first sample in the waveform was acquired, t0, and the amount of time that elapsed between each sample, dt. However, there are limitations on these two values.
Line Format (Boolean)
The line format represents each line within a channel as a single Boolean value (a single byte). The states of the data are limited to 1s (true) and 0s (false). Line formats are only provided for single sample reads and writes.
Use the line format when it is convenient for manipulating or displaying the digital data. A typical application is controlling or reading back relay states. For high-speed digital applications, you should generally not use the line format.
Port Format (Integer)
The port format matches the native format of digital devices that can represent only two digital states and organize individual lines into collections known as ports. For more information, refer to Digital Data—Integer Format
The port format is the most efficient in terms of space, as it requires only a bit of memory per line. In addition, the port format is often the most efficient in time as it matches the native format of many devices.
The largest integer supported is 32 bits; therefore, you can read and write digital channels with no more than 32 lines when using the port format.
Counter Channel Data Formats
64-Bit Floating-Point Numbers
The 64-bit floating-point number format reads scaled data. This format is best when you want to work with data in engineering units.
Unsigned Integers
The unsigned integer format reads data in the native format of the device. Use this format for maximum performance. The tradeoff is that your application will have to understand how to interpret and manipulate data that is not in engineering units.
Raw Data Formats
The raw data format is defined by the native data format of the device.