Use NI-VISA vs. the NI-VXI API

National Instruments recommends using NI-VISA, rather than the NI-VXI API, to develop your VXI/VME applications. Both APIs can perform message-based communication with VXI instruments, do high- and low-level communication over the VXI backplane, perform block transfers, and handle asynchronous events. However, NI-VXI (that is, the software package that ships with National Instruments controllers and includes utilities such as Measurement & Automation Explorer and Resman) is optimized for use through NI-VISA.

If you are using GPIB or serial instruments, or if your VXI instruments are connected via a GPIB-VXI/C, you probably want to use NI-VISA because the API is interface independent. The calls you use to send messages to GPIB instruments are the same as those used to send messages to VXI instruments. NI-VISA also supports asynchronous I/O operations, whereas the NI-VXI API does not.

The NI-VXI API supports certain legacy instruments and behaviors that NI-VISA does not support, such as RORA interrupters and asynchronous notification of bus errors (note that VISA does report bus errors from high-level bus access functions).

You can use both interfaces in the same program, though it is not recommended unless you need functionality from both APIs. You should not try to handle asynchronous events with both languages. If you need to handle asynchronous events, such as VXI interrupts or triggers, you should choose one API and use that for all asynchronous operations.