For any application you write, open a session to establish communication with the instrument by using one of the following two VIs or functions:

LabVIEW VIs C Functions
niHSDIO Init Acquisition Session niHSDIO_InitAcquisitionSession
niHSDIO Init Generation Session niHSDIO_InitGenerationSession
niHSDIO Init Ext Cal niHSDIO_InitExtCal
Use these functions for both dynamic and static data operations. Use the ViSession handle or instrument handle returned by these VIs or functions to identify the NI device in all subsequent NI-HSDIO function calls.
Tip Do not confuse these three functions with the niHSDIO Initiate VI or the niHSDIO_Initiate function, which are used to start a dynamic operation.

In addition to establishing a session with the device, these VIs and functions also send initialization commands to set the device to the state necessary for the instrument driver. These two functions can perform a number of additional tasks, such as verifying that the instrument driver is valid for the device and resetting the device to a known state.