Technical data

146 Chapter 9
Programming Examples
Programming in C Using the VISA
Programming Examples
The session returned from viOpenDefaultRM must be used in the sesn
parameter of the viOpen function. The viOpen function then uses that
session and the device address specified in the rsrcName parameter to
open a device session. The vi parameter in viOpen returns a session
identifier that can be used with other VISA functions.
Your program may have several sessions open at the same time by
creating multiple session identifiers by calling the viOpen function
multiple times.
The following summarizes the parameters in the previous function
calls:
sesn This is a session returned from the viOpenDefaultRM
function that identifies the resource manager session.
rsrcName This is a unique symbolic name of the device (device
address).
accessMode This parameter is not used for VISA. Use VI_NULL.
timeout This parameter is not used for VISA. Use VI_NULL.
vi This is a pointer to the session identifier for this
particular device session. This pointer will be used to
identify this device session when using other VISA
functions.
The following is an example of opening sessions with a GPIB
multimeter and a spectrum analyzer on LAN:
ViSession defaultRM, dmm, sa;
.
.
viOpenDefaultRM(&defaultRM);
viOpen (defaultRM, "GPIB0::22::INSTR", VI_NULL,
VI_NULL, &dmm);
viOpen (defaultRM, "TCPIP0::192.168.0.2::inst0::INSTR",
VI_NULL,
VI_NULL, &sa);
.
.
viClose (sa);
viClose (dmm);
viClose(defaultRM);
The above function first opens a session with the default resource
manager. The session returned from the resource manager and a device
address is then used to open a session with the GPIB device at address
22. That session will now be identified as dmm when using other VISA
functions. The session returned from the resource manager is then used
to open a session with the LAN device at IP Address 192.168.0.2. That
session will now be identified as sa when using other VISA functions.
See the following section for information on addressing particular