Opening A Session; Device Sessions - Keysight N9320B Programmer's Manual

Programming Example
Programming in C using the VTL

Opening a Session

N O T E

Device Sessions

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A session is a channel of communication. Sessions must first be
opened on the default resource manager, and then for each device
you will be using. The following is a summary of sessions that can
be opened:
• A resource manager session is used to initialize the VISA system.
It is a parent session that knows about all the opened sessions.
A resource manager session must be opened before any other
session can be opened.
• A device session is used to communicate with a device on an
interface. A device session must be opened for each device you
will be using. When you use a device session you can
communicate without worrying about the type of interface to
which it is connected. This insulation makes applications more
robust and portable across interfaces. Typically a device is an
instrument, or a computer.
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 re-open with all devices connected
and in working condition.
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.