User`s guide

Programming via GPIB and VXI 4

Agilent VISA User’s Guide 95

using VISA, you can place the SCPI command within your

VISA output function call. Then, the message- based device

interprets the SCPI command. In this case you can use the

VISA formatted I/O or non- formatted I/O functions and

program the message- based device as you would a GPIB

device.

However, if the message- based device has shared memory,

you can access the device's shared memory by doing register

peeks and pokes. VISA provides two different methods you

can use to program directly to the registers: high- level

memory functions or low- level memory functions.

A register- based VXI device typically does not have a

processor to interpret high- level commands. Therefore, the

device must be programmed with register peeks and pokes

directly to the device's registers. VISA provides two different

methods you can use to program register- based devices:

high- level memory functions or low- level memory functions.

GPIB Interfaces Overview

As shown in the following figure, a typical GPIB interface

consists of a Windows PC with one or more GPIB cards (PCI

and/or ISA) cards installed in the PC, and one or more

GPIB instruments connected to the GPIB cards via GPIB

cable. I/O communication between the PC and the

instruments is via the GPIB cards and the GPIB cable. The

following figure shows GPIB instruments at addresses 3 and