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

4.

The polling continues until SRQ is unasserted or an error condition 
is detected. 

5.

To empty the queue, use the 

ibrsp

 function. 

ibrsp

 returns the first 

queued response. Other responses are read in first-in-first-out (FIFO) 
fashion. If the RQS bit of the status word is not set when 

ibrsp

 is 

called, a serial poll is conducted and returns the response received. 
To prevent queue overflow, empty the queue as soon as an automatic 
serial poll occurs.

6.

If the RQS bit of the status word is still set after 

ibrsp

 is called, the 

response byte queue contains at least one more response byte. If this 
happens, continue to call 

ibrsp

 until the RQS bit is cleared from the 

status word.

If autopolling is enabled and the GPIB interface detects an SRQ, the driver 
serial polls all open devices connected to that interface. The serial poll 
continues until either SRQ unasserts or all the devices have been polled.

If no device responds positively to the serial poll, or if SRQ remains in 
effect because of a faulty instrument or cable, a stuck SRQ state is in effect. 
If this happens during an 

ibwait

 for RQS, the driver reports the ESRQ 

error. If the stuck SRQ state happens, no further polls are attempted until an 

ibwait

 for RQS is made. When 

ibwait

 is issued, the stuck SRQ state is 

terminated and the driver attempts a new set of serial polls. 

If autopolling is enabled, the NI-488.2 software can perform autopolling 
after any device-level call provided that no GPIB I/O is currently in 
progress. Because the driver uses interrupts, an automatic serial poll can 
occur even when your application is not making any calls to the NI-488.2 
software. Autopolling can also occur when a device-level 

ibwait

 for RQS 

is in progress. Autopolling is not allowed when an application calls a 
board-level traditional or multi-device NI-488.2 call, or the stuck 
SRQ (ESRQ) condition occurs.