National Instruments NI-488.2 NI-488.2 User Manual page 95

Data Lines
Handshake Lines
Interface Management Lines
© National Instruments Corporation
Eight data lines, DIO1 through DIO8, carry both data and command
messages.
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.
Line
NRFD
(not ready for data)
NDAC
(not data accepted)
DAV
(data valid)
Five hardware lines manage the flow of information across the bus.
Table A-2 summarizes the GPIB interface management lines.
Table A-2. GPIB Interface Management Lines
Line
ATN
(attention)
IFC
(interface clear)
REN
(remote enable)
Table A-1. GPIB Handshake Lines
Description
Listening device is ready/not ready to receive a
message byte. Also used by the Talker to signal
high-speed (HS488) GPIB transfers.
Listening device has/has not accepted a message
byte.
Talking device indicates signals on data lines are
stable (valid) data.
Description
Controller drives ATN true when it sends
commands and false when it sends data messages.
System Controller drives the IFC line to initialize
the bus and make itself CIC.
System Controller drives the REN line to place
devices in remote or local program mode.
A-3
Appendix A GPIB Basics
NI-488.2 User Manual