Ndac (Not Data Accepted; Dav (Data Valid; Interface Management Lines; Atn (Attention - National Instruments Corporation GPIB-1014P User Manual

Appendix E Multiline Interface Messages

NDAC (not data accepted)

NDAC indicates when a device has or has not accepted a message byte. The line is driven by all
devices when receiving commands and by Listeners when receiving data messages.

DAV (data valid)

DAV tells when the signals on the data lines are stable (valid) and can be accepted safely by devices.
The Controller drives DAV when sending commands and the Talker drives it when sending data
messages.

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.
The Controller uses the EOI line to tell devices to identify their response in a parallel poll.

Physical and Electrical Characteristics

Devices are usually connected with a cable assembly consisting of a shielded 24 conductor cable
with both a plug and receptacle connector at each end. This design allows devices to be linked in
either a linear or a star configuration, or a combination of the two. See Figures E-1, E-2, and E-3.
The standard connector is the Amphenol or Cinch Series 57 Microribbon or Amp Champ type. An
adapter cable using a non-standard cable and/or connector is used for special interconnection
applications.
© National Instruments Corporation E-3 GPIB-1014P User Manual