National Instruments NI-488.2 - Manual (Page 96)

Appendix A GPIB Basics
NI-488.2 User Manual A-4 ni.com
SRQ
(service request) Any device can drive the SRQ line to
asynchronously request service from the Controller.
EOI
(end or identify) Talker uses the EOI line to mark the end of a data
message. Controller uses the EOI line when it
conducts a parallel poll.
Table A-2. GPIB Interface Management Lines (Continued)
Line Description