User`s guide

94 Agilent VISA User’s Guide
4 Programming via GPIB and VXI
GPIB and VXI Interfaces Overview
This section provides an overview of the GPIB, GPIB- VXI,
and VXI interfaces, including:
• General Interface Information
• GPIB Interfaces Overview
• VXI Interfaces Overview
General Interface Information
VISA supports three interfaces you can use to access
instruments or devices: GPIB, VXI, and GPIB- VXI. The GPIB
interface can be used to access VXI instruments via a
Command Module. In addition, the VXI backplane can be
directly accessed with the VXI or GPIB- VXI interfaces.
What is an I/O Interface?
An I/O interface can be defined as both a hardware
interface and as a software interface. Connection Expert is
used to associate a unique interface name with a hardware
interface. Agilent IO Libraries Suite uses a VISA interface
name to identify an interface. This information is passed in
the parameter string of the viOpen function call in a VISA
program.
Connection Expert assigns a VISA interface name to the
interface hardware, and other necessary configuration values
for an interface when the interface is configured. See the
Agilent IO Libraries Suite Online Help for details.
VXI Device Types
When using GPIB- VXI or VXI interfaces to directly access
the VXI backplane (in the VXI mainframe), you must know
whether you are programming a
message- based or a
register- based VXI device (instrument).
A message- based VXI device has its own processor that
allows it to interpret high- level commands such as Standard
Commands for Programmable Instruments (SCPI). When