VISA Resource Name Control

Use the VISA resource name control, located on the Controls»I/O palette, to specify the resource a VISA session will be opened to and maintain the session and class. The dup VISA resource name is a copy of the VISA resource name that is passed out of the VISA functions. By passing the resource name in and out of functions, you can simplify dataflow programming by chaining functions together. This is similar to the dup file refnums used by the File I/O functions.

By default, the VISA resource name is set to the Instr class, which also corresponds to the class of the session to be opened. You can change the class type by right-clicking the VISA resource name control in edit mode and selecting a different class. The following classes are currently supported:

I/O Session

Event Class

Resource Manager

Note  The Generic Event, Service Request Event, Trigger Event, VXI Signal Event, VXI/VME Interrupt Event, and Resource Manager classes can only be passed in as a VISA resource name with the VISA Close function and a Property Node.

VISA functions vary in the class of VISA resource name, which can be wired to them. The valid classes for each function are listed in the NI-VISA Programmer Reference Manual. For example, the functions on the High Level Register Access and Low Level Register Access palettes do not accept VISA sessions of class GPIB Instr or Serial Instr. If you wire VISA resource name to a function that does not accept the class of the session, or if you wire two VISA resource names of differing classes together, your block diagram will not run and a Class Conflict error is reported.