National Instruments NI-VXI

Overview of NI-VXI

Chapter

This chapter introduces you to the concepts of VXI (VME eXtensions

for Instrumentation), VME, MXI (Multisystem eXtension Interface),

and their relationship to the NI-VXI application programmer’s

interface (API).

Comprehensive functions for programming the VXIbus/VMEbus are

included with the NI-VXI software. They are available for a variety of

controller platforms and operating systems. Among the compatible

platforms are the National Instruments line of embedded controllers

and external computers that have a MXIbus interface.

Note: The following chapter discusses features unique to VXI as well as

common VXI/VME features. VME users can skip to the section entitled

Interrupts and Asynchronous Events.

VXIbus Overview

Concepts of the VXIbus specification include the VXI device,

message-based devices, the World Serial Protocol, the

Commander/Servant hierarchy, and hardware interrupts and

asynchronous events.

VXI Devices

A VXI device has a unique logical address, which serves as a means of

referencing the device in the VXI system. This logical address is

analogous to a GPIB device address. VXI uses an 8-bit logical address,

allowing for up to 256 VXI devices in a VXI system.

Each VXI device must have a specific set of registers, called

configuration registers (Figure 1-1) .These registers are located in the

upper 16 KB of the 64 KB A16 VME address space. The logical

address of a VXI device determines the location of the device’s

configuration registers in the 16 KB area reserved by VXI.