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3
C H A P T E R
Basic GPIB Concepts
The information in this basic concepts discussion is normally not necessary to
successfully operate the FPM-8200 through its GPIB interface, because your
computer's GPIB controller will usually handle them for you. However this is a
useful perspective in understanding GPIB.
Data and Interface Messages
GPIB devices communicate with each other by sending data and interface
messages. Data contains device-specific information such as programming
instructions, measurement results, and instrument status. Each device has an
address number, and ignores all data traffic not addressed to it. Depending on its
content, data is often called a "device dependent message" or a "device
dependent command". Interface messages manage the bus, with functions such
as initializing the bus and addressing or unaddressing devices. In addition, some
individual bus lines are designated for this purpose (see Figure 3.1). The end of
this chapter includes information on interface messages supported by the FPM-
8200.
Talkers, Listeners, and Controllers
Every GPIB system consists of one or more "talkers" and "listeners", and often at
least one "controller". Talkers supply data. Listeners accept data. A system can
consist of simply a talker and listener, for example a meter connected to a
datalogger or chart recorder. Controllers designate talkers and listeners. A
controller is necessary when the active talkers or listeners must be changed.
When the controller is a computer, it often also designates itself as a listener so it
can collect data from designated talkers.
If there is more than one controller, only one can be the Controller In Charge
(CIC). Control can be passed from one controller to another. In a multiple
controller system, there can be one "System Controller" capable of asserting
control (becoming CIC).
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FPM-8200
R E M O T E O P E R A T I O N
Basic GPIB Concepts
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