National Instruments NI-488.2 Benutzerhandbuch

© National Instruments Corporation

char SerialPollResponse = 0;

ibwait ( DeviceHandle, TIMO | RQS );

if ( ibsta & RQS )  {

printf ( "Device asserted SRQ.\n" );

/* Use ibrsp to retrieve the serial poll response. */

ibrsp ( DeviceHandle, &SerialPollResponse );

}

return SerialPollResponse;

}

The NI-488.2 software includes a set of multi-device NI-488.2 calls that 
you can use to conduct SRQ servicing and serial polling. Calls pertinent to 
SRQ servicing and serial polling are 

AllSpoll

, 

ReadStatusByte

, 

FindRQS

, 

TestSRQ

, and 

WaitSRQ

. Following are descriptions of each of 

the calls:

•

AllSpoll

 can serial poll multiple devices with a single call. It places 

the status bytes from each polled instrument into a predefined array. 
Then, you must check the RQS bit of each status byte to determine 
whether that device requested service.

•

ReadStatusByte

 is similar to 

AllSpoll

, except that it only serial 

polls a single device. It is also similar to the device-level NI-488.2 

ibrsp

 function.

•

FindRQS

 serial polls a list of devices until it finds a device that is 

requesting service or until it has polled all of the devices on the list. 
The call returns the index and status byte value of the device requesting 
service.

•

TestSRQ

 determines whether the SRQ line is asserted and returns to 

the program immediately.

•

WaitSRQ

 is similar to 

TestSRQ

, except that 

WaitSRQ

 suspends the 

application until either SRQ is asserted or the timeout period is 
exceeded.

The following examples use these calls to detect SRQ and then determine 
which device requested service. In these examples, three devices are 
present on the GPIB at addresses 3, 4, and 5, and the GPIB interface is 
designated as bus index 0. The first example uses 

FindRQS

 to determine 

which device is requesting service, and the second example uses 

AllSpoll

 

to serial poll all three devices. Both examples use 

WaitSRQ

 to wait for the 

GPIB SRQ line to be asserted.