© National Instruments
|
A-3
GPIB-140A User Manual
Handshake Lines
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.
Interface Management 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
Line
Description
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
Line
Description
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.
