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Chapter 7 NI-488.2 Programming Techniques
NI-488.2 User Manual for Windows 7-4 www.natinst.com
Waiting for GPIB Conditions
You can use the
ibwait
function to obtain the current
ibsta
value or to
suspend your application until a specified condition occurs on the GPIB. If
you use
ibwait
with a parameter of zero, it immediately updates
ibsta
and returns. If you want to use
ibwait
to wait for one or more events to
occur, pass a wait mask to the function. The wait mask should always
include the TIMO event; otherwise, your application is suspended
indefinitely until one of the wait mask events occurs.
Asynchronous Event Notification in Win32
NI-488.2 Applications
Win32 NI-488.2 applications can asynchronously receive event
notifications using the
ibnotify
function. This function is useful if you
want your application to be notified asynchronously about the occurrence
of one or more GPIB events. For example, you might choose to use
ibnotify
if your application only needs to interact with your GPIB device
when it is requesting service. After calling
ibnotify
, your application
does not need to check the status of your GPIB device. Then, when your
GPIB device requests service, the NI-488.2 driver automatically notifies
your application that the event has occurred by invoking a callback
function. The callback function is registered with the NI-488.2 driver when
the
ibnotify
call is made.
Calling the ibnotify Function
ibnotify
has the following function prototype:
ibnotify (
int ud,// unit descriptor
int mask,// bit mask of GPIB events
GpibNotifyCallback_t Callback,
// callback function
void * RefData// user-defined reference data
)
Both board-level and device-level
ibnotify
calls are supported by the
NI-488.2 driver. If you are using device-level calls, you call
ibnotify
with a device handle for
ud
and a
mask
of RQS, CMPL, END, or TIMO. If
you are using board-level calls, you call
ibnotify
with a board handle for
ud
and a
mask
of any values except RQS or ERR. The
ibnotify
mask bits
are identical to the
ibwait
mask bits. In the example of waiting for your