National Instruments NI-488.2 ユーザーズマニュアル

© National Instruments Corporation

GPIB device to request service, you might choose to pass 

ibnotify

 a 

mask

 with RQS (for device-level) or SRQI (for board-level). 

The callback function that you register with the 

ibnotify

 call is invoked 

by the NI-488.2 driver when one or more of the mask bits passed to 

ibnotify

 is TRUE. The function prototype of the callback is as follows:

int __stdcall Callback (

int ud,// unit descriptor

int ibsta,// ibsta value

int iberr,// iberr value

long ibcntl,// ibcntl value

void * RefData// user-defined reference data 

)

The callback function is passed a unit descriptor, the current values of the 
NI-488.2 global variables, and the user-defined reference data that was 
passed to the original 

ibnotify

 call. The NI-488.2 driver interprets the 

return value for the callback as a mask value that is used to automatically 
rearm the callback if it is non-zero. For a complete description of 

ibnotify

, refer to the NI-488.2 online help. For instructions on accessing 

the online help, refer to the 

 section in 

The 

ibnotify

 callback is executed in a separate thread of execution from the rest 

of your application. If your application will be performing other NI-488.2 operations while 
it is using 

ibnotify

, use the per-thread NI-488.2 globals that are provided by the 

ThreadIbsta

, 

ThreadIberr

, 

ThreadIbcnt

, and 

ThreadIbcntl

 functions described 

in the 

 section of this chapter. In 

addition, if your application needs to share global variables with the callback, use a 
synchronization primitive (for example, a semaphore) to protect access to any globals. For 
more information about the use of synchronization primitives, refer to the documentation 
about using Win32 synchronization objects that came with your development tools.

The following code is an example of how you can use 

ibnotify

 in your 

application. Assume that your GPIB device is a multimeter that you 
program it to acquire a reading by sending "

SEND DATA"

. The multimeter 

requests service when it has a reading ready, and each reading is a floating 
point value.

In this example, globals are shared by the 

Callback

 thread and the main 

thread, and the access of the globals is not protected by synchronization. 
In this case, synchronization of access to these globals is not necessary