National Instruments GPIB-120A - Manual (Page 22)

Operation of the GPIB Appendix A
GPIB-120A User Manual A-4 © National Instruments Corporation
Interface Management Lines
Five lines are used to manage the flow of information across the interface.
ATN (Attention)
The Controller drives ATN true when it uses the data lines to send commands and false when it
allows a Talker to send data messages.
IFC (Interface Clear)
The System Controller drives the IFC line to initialize the bus and become CIC.
REN (Remote Enable)
The System Controller drives the REN line, which is used to place devices in remote or local
program mode.
SRQ (Service Request)
Any device can drive the SRQ line to asynchronously request service from the Controller.
EOI (End Or Identify)
The EOI line has two purposes: the Talker uses the EOI line to mark the end of a message
string, and the Controller uses the EOI line to tell devices to identify their response in a parallel
poll.