User Manual

Chapter 6 551
Programming Fundamentals
Programming in C Using the VTL
Programming Fundamentals
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 VTL. Use VI_NULL.
timeout This parameter is not used for VTL. 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 VTL
functions.
The following is an example of opening sessions with a GPIB
multimeter and a GPIB-VXI scanner:
ViSession defaultRM, dmm, scanner;
.
.
viOpenDefaultRM(&defaultRM);
viOpen (defaultRM, "GPIB0::22::INSTR", VI_NULL,
VI_NULL, &dmm);
viOpen (defaultRM, "GPIB-VXI0::24::INSTR", VI_NULL,
VI_NULL, &scanner);
.
.
viClose (scanner);
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 VTL
functions. The session returned from the resource manager is then used
againwithanotherdeviceaddresstoopenasessionwiththeGPIB-VXI
device at primary address 9 and VXI logical address 24. That session
will now be identified as scanner when using other VTL functions. See
the following section for information on addressing particular devices.
Addressing a Session
As seen in the previous section, the rsrcName parameter in the viOpen
function is used to identify a specific device. This parameter is made up
of the VTL interface name and the device address. The interface name
is determined when you run the VTL Configuration Utility. This name