Technical data

Programming Example 4
Programmer’s Guide 33
Programming in C using the VTL
This section includes some basic information about programming in the
C language using Agilent VISA transition library (VTL). Note that
some of this information may not be relevant to your particular
application. For example, if you are not using VXI instruments, the VXI
references will not be relevant.
Typical Example Program Contents
The following table summaries the VTL function calls used in the
example programs.
visa.h This file is included at the beginning of the each file to provide the function
prototypes and constants defined by VTL. For C and C++ programs, you must
include the visa.h header file at the beginning of every file that contains VISA
function calls: #include “visa.h”
ViSession The ViSession is a VTL data type. Each object that will establish a communication
channel must be defined as ViSession. Sessions must firstly be opened on the
default resource manager, and then for each resource you will be using.
viOpenDefaultRM You must first open a session with the default resource manager with the
viOpenDefaultRM function, and then for each resource you will be using. This
function will initialize the default resource manager and return a pointer to that
resource manager session.
viOpenDefaultRM(&sesn)
viOpen This function establishes a communication channel with the device specified. A
session identifier that can be used with other VTL functions is returned. This call
must be made for each device you will be using.
viOpenDefaultRM(&sesn)
viOpen(sesn, rsrcName, accessMode, timeout, &vi)
viPrintf
viScanf
These are the VTL formatted I/O functions that are patterned after those used in the C
programming language. The viPrintf call sends the SCPI commands to the
analyzer. The viPrintf call can also be used to query the analyzer. The viScanf
call is then used to read the results.
viWrite This function synchronously sends the data pointed to by buf to the device specified
by vi. Only one synchronous write operation van occur at any one time.
viWrite(vi, buf, count, &retCount)