Initiate and Fetch

Use the Initiate and Fetch functions to perform other operations while the device acquires data. Initiate begins the acquisition operation and returns control to your program. Fetch transfers the acquired data from acquisition onboard memory to your application.

The Initiate and Fetch VIs/functions are shown in the following table.

Note  If you are programming in C, you must declare an array in your program. This array allocates space for the data that is acquired with the fetch functions. LabVIEW users do not need to declare an array because the Fetch VIs allocate the array.

If you fetch the data while the device is still acquiring, the function waits until all the requested data has been acquired. If the data is not acquired within the time specified with the timeout parameter, NI-HSDIO returns an error. If you want to stop the device before it finishes, use the niHSDIO Abort VI or the niHSDIO_Abort function. However, you cannot fetch after aborting.

Tip  Read the NIHSDIO_ATTR_FETCH_BACKLOG attribute before calling the fetch function to determine the number of samples available, or use the Fetch Backlog property in LabVIEW (Dynamic Acquisition»Fetch Backlog) for the same purpose.

Note  The read functions combine the initiate and fetch functions into one call. The read functions are more suitable for simple acquisitions, while initiate/fetch is better suited for complex applications that involve triggering.