Agilent Technologies E2094S, Руководство пользователя, Страница: 47 / 146

Programming with VISA
3
Agilent VISA User’s Guide 47
The queuing and callback mechanisms are suitable for different
programming styles. The queuing mechanism is generally useful for
non-critical events that do not need immediate servicing. The callback
mechanism is useful when immediate responses are needed. These
mechanisms work independently of each other, so both can be enabled
at the same time. By default, a session is not enabled to receive any
events by either mechanism.
The viEnableEvent operation can be used to enable a session to
respond to a specified event type using either the queuing mechanism,
the callback mechanism, or both. Similarly, the
viDisableEvent
operation can be used to disable one or both mechanisms. Because the
two methods work independently of each other, one can be enabled or
disabled regardless of the current state of the other.
Events that can be Enabled
The following table shows the events that are implemented for Agilent
VISA for each resource class, where AP = Access Privilege, RO - Read
Only, and RW = Read/Write. Note that some resource classes/events,
such as the
SERVANT class, are not implemented by Agilent VISA and
are not listed in the following tables.
Once the application has received an event, information about that event
can be obtained by using the
viGetAttribute function on that particular
event context. Use the VISA viReadSTB function to read the status
byte of the service request.
.
Table 11 Instrument Control (INSTR) Resource Events
VI_EVENT_SERVICE_REQUEST
Notification that a service request was received from the device.
Event Attribute Description A
P Data Type Range
VI_ATTR_EVENT_TYPE Unique logical identifier of the
event. R
O ViEventTy
pe VI_EVENT_SERVICE_RE
Q
VI_EVENT_VXI_SIGP
Notification that a VXIbus signal or VXIbus interrupt was received from the device.