Technical data

620 Agilent N8201A Performance Downconverter Synthetic Instrument Module, 250 kHz to 26.5 GHz
28 Programming Fundamentals
Device Sessions
There are two parts to opening a communications session with a specific device. First you
must open a session to the default resource manager with the viOpenDefaultRM
function. The first call to this function initializes the default resource manager and returns a
session to that resource manager session. You only need to open the default manager
session once. However, subsequent calls to viOpenDefaultRM returns a session to a
unique session to the same default resource manager resource.
Next, you open a session with a specific device with the viOpen function. This function
uses the session returned from viOpenDefaultRM and returns its own session to
identify the device session. The following shows the function syntax:
viOpenDefaultRM (sesn);
viOpen (sesn, rsrcName, accessMode, timeout, vi);
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 VTL 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 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:
NOTE
All devices that you will be using need to be connected and in working condition prior to the
first VTL function call (viOpenDefaultRM). The system is configured only on the first
viOpenDefaultRM per process. Therefore, if viOpenDefaultRM is called without
devices connected and then called again when devices are connected, the devices will not
be recognized. You must close ALL resource manager sessions and reopen with all devices
connected and in working condition.