VISA Access Mechanisms

The following sections summarize the most important characteristics of attributes, events, and operations. Refer to VISA Overview for a more detailed description of this subject.

Attributes

An attribute describes a value within a session or resource that reflects a characteristic of the operational state of the given object. These attributes are accessed through the following operations:

• viGetAttribute ()
• viSetAttribute ()

Events

An event is an asynchronous occurrence that is independent of the normal sequential execution of the process running in a system. Depending on how you want to handle event occurrences, you can use the viEnableEvent () operation with either the viInstallHandler () operation or the viWaitOnEvent () operation.

Events respond to attributes in the same manner that resources do. Once your application is done using a particular event received via viWaitOnEvent (), it should call viClose () to destroy that event.

Operations

An operation is an action defined by a resource that can be performed on the given resource. Each resource has the ability to define a series of operations. In addition to those defined by each resource, you can use the following template operations in any resource:

• viClose ()
• viGetAttribute ()
• viSetAttribute ()
• viStatusDesc ()
• viTerminate ()
• viLock ()
• viUnlock ()
• viEnableEvent ()
• viDisableEvent ()
• viDiscardEvents ()
• viWaitOnEvent ()
• viInstallHandler ()
• viUninstallHandler ()