Chapter 3
Developing Your Application
PCI-Based MXI-2 Interfaces for Windows 2000/NT/Me/98
3-6
ni.com
You can also access VXI and VME devices configured in A16, A24, or
A32 space by opening the VXI MEMACC resource, VISA’s representation
of VXI memory. For more information about VISAIC operations and
commands, refer to the online help in the
Help
menu and the
context-sensitive help (such as
What’s This?
) available by right-clicking
in any panel.
Programming for VXI
NI-VISA and the NI-VXI API are the two National Instruments
programming interfaces for accessing your VXI/VME instruments. With
NI-VXI 3.0 or later, NI-VISA is the native API for communicating with a
VXI or VME system, and we recommend using it for all new applications.
Older programs that use the NI-VXI API now use the NI-VXI-to-NI-VISA
compatibility layer to communicate with the VXI devices. Using this layer,
older programs can run in NI-VXI 3.0 or later without being rewritten to
use the VISA interface.
Note
The NI-VXI API development environment is not installed by default as part of the
NI-VXI installation. If you must develop an application using the older NI-VXI API, run
the NI-VXI installer and select the appropriate option in the custom installation screen.
Be sure to review the
section later in this chapter.
NI-VISA is the National Instruments implementation of the VISA API as
the VXI
plug&play
standard defines. It provides a common interface to
many types of instruments (such as VXI, GPIB, PXI, Serial, TCP/IP, etc.)
and therefore is especially useful in situations where you are using multiple
types of instruments.
Both NI-VISA and the NI-VXI API include functions for register-level
access to VXI instruments and messaging capability to message-based
devices. You can also use either interface to service asynchronous events
such as triggers, signals, and interrupts, and also assert them. Compatibility
with the NI-VXI API is included for legacy applications only—we
recommend that you write all new VXI/VME applications in VISA.
The best way to learn NI-VISA programming is by reviewing the example
programs your software includes. The examples directory contains working
VISA programs that illustrate many different types of applications. You can
find these examples in the
VXIpnp\Win
XX
\NIvisa\Examples
directory.
If you are just getting started, you should learn how to access registers
with high-level calls and send messages with word-serial functions.
