National Instruments NI-488.2 Benutzerhandbuch

© National Instruments Corporation

You can enable automatic serial polling if you want your application to 
conduct a serial poll automatically when the SRQ line is asserted. The 
autopolling procedure occurs as follows:

1.

To enable autopolling, use the configuration function, 

ibconfig

, with 

option 

IbcAUTOPOLL

, or the NI-488.2 Configuration utility. 

(Autopolling is enabled by default.)

2.

When the SRQ line is asserted, the driver automatically serial polls the 
open devices. 

3.

Each positive serial poll response (bit 6 or hex 40 is set) is stored in a 
queue associated with the device that sent it. The RQS bit of the device 
status word, 

ibsta

, is set. 

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. 
Empty the queue as soon as an automatic serial poll occurs, because 
responses might be discarded if the queue is full.

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 RQS is cleared.

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.