Operation of the GPIB
Appendix C
GPIB-110 User Manual
C- 2
© National Instruments Corporation
The role of the GPIB Controller can also be compared to the role of the CPU of a computer, but
a better analogy is to the switching center of a city telephone system.
The switching center (Controller) monitors the communications network (GPIB). When the
center (Controller) notices that a party (device) wants to make a call (send a data message), it
connects the caller (Talker) to the receiver (Listener).
The Controller usually addresses a Talker and a Listener before the Talker can send its message
to the Listener. After the message is transmitted, the Controller usually unaddresses both
devices.
Some bus configurations do not require a Controller. For example, one device may only be a
Talker (called a Talk-only device) and there may be one or more Listen-only devices.
A Controller is necessary when the active or addressed Talker or Listener must be changed. The
Controller function is usually handled by a computer.
With the GPIB interface board, your personal computer plays all three roles.
•
Controller–manages the GPIB
•
Talker–sends data
•
Listener–receives data
Controller-In-Charge and System Controller
Although there can be multiple Controllers on the GPIB, only one Controller at a time is Active
Controller or Controller-in-Charge (CIC). Active control can be passed from the current Active
Controller to an idle Controller. Only one device on the bus, the System Controller, can make
itself the CIC.
GPIB Signals and Lines
The interface bus consists of 16 signal lines and 8 ground return or shield drain lines. The 16
signal lines are divided into three groups:
•
Eight data lines
•
Three handshake lines
•
Five interface management lines
