ILX Lightwave LDC-3700C Series, User Manual, Page: 60 / 176

R E M O T E O P E R A T I O N
Basic GPIB Concepts
44
LDC-3700C Series
C H A P T E R
3

Basic GPIB Concepts
GPIB (General Purpose Interface Bus) is the common name for ANSI/IEEE
Standard 488.2-1987 , an industry standard for interconnecting test instruments in
a system. The information in this basic concepts discussion is normally not
necessary to successfully operate the LDC-3700C through its GPIB interface,
because your computer's GPIB controller usually handles 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.
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).