National Instruments NI-488.2 Benutzerhandbuch

© National Instruments Corporation

Three hardware handshake lines asynchronously control the transfer of 
message bytes between devices. This process is a three-wire interlocked 
handshake, and it guarantees that devices send and receive message bytes 
on the data lines without transmission error. Table A-1 summarizes the 
GPIB handshake lines. 

Five hardware lines manage the flow of information across the bus. 
Table A-2 summarizes the GPIB interface management lines. 

Table A-1.  GPIB Handshake Lines

NRFD 
(not ready for data)

Listening device is ready/not ready to receive a 
message byte. Also used by the Talker to signal 
high-speed GPIB transfers.

NDAC 
(not data accepted)

Listening device has/has not accepted a message 
byte.

DAV 
(data valid)

Talking device indicates signals on data lines are 
stable (valid) data.

Table A-2.  GPIB Interface Management Lines

ATN 
(attention)

Controller drives ATN true when it sends 
commands and false when it sends data messages.

IFC 
(interface clear)

System Controller drives the IFC line to initialize 
the bus and make itself CIC.

REN 
(remote enable)

System Controller drives the REN line 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)

Talker uses the EOI line to mark the end of a data 
message. Controller uses the EOI line when it 
conducts a parallel poll.