Operation of the GPIB
Appendix D
GPIB-232CT User Manual
D-6
© National Instruments Corp.
IFC* (interface clear)
The System Controller drives the IFC* line to initialize the bus and become
Controller-In-Charge.
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 Active Controller with the SRQ* line.
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 D-2 and D-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.
The GPIB uses negative logic with standard TTL logic levels. When DAV*
is true, for example, it is a TTL low level ( • 0.8V), and when DAV* is
false, it is a TTL high level ( • 2.0V).
