Page 1063 - The Mechatronics Handbook

R R R
T T

D D

T1 R R R T2

D D D

T3 T4 T32

FIGURE 37.11 Example of an RS-485 multipoint application.

As mentioned earlier, data sheets and application notes of component suppliers provide an excellent
source of information [1,2]. An excellent overview of practical data communications and interfacing for
instrumentation and control is provided in [7]. Detailed discussion of design aspects of serial commu-
nications and interfacing based on RS-232 and RS-485 is given in [8]. It is recommended that for the
full specification the designer should consult the relevant standards [4–6]. Additional information includ-
ing design recommendations can be found in [9–11]. A good introduction and background theory to
data communication and computer networks can be found in [12].

37.3 IEEE 488—The General Purpose Interface Bus (GPIB)

Introduction
The interface described by IEEE 488 standard, which will be referred to as GPIB in this chapter, is used
to connect instruments to test and measurement systems. Examples of such instruments are digital
voltmeters, storage oscilloscopes, printers, and plotters. In general, these instruments are called GPIB
devices. These devices operate under the coordination of a controller. Most modern systems consist of
a cluster of such devices connected to one or more computers. In such a system, one of the computers
will become the controller.
Historically, the interface was developed by Hewlett–Packard in 1965. At that time, the interface was
called HPIB, and a general standard did not exist. In 1975, it was formulated as IEEE 488 and was called
IEEE Standard Digital Interface for Programmable Instrumentation. The standard specified the electrical,
mechanical, and hardware aspects, i.e., the signals, their functioning, and purpose. Instrument manufac-
turers used the interface freely without adhering to a standard protocol in communicating with instruments.
Instruments meant for the same purpose, yet manufactured by different manufacturers required widely
varied commands. Some instruments made measurements in response to a command, while some other
instruments of similar type made measurements without a command at all. Further, there were no agreed
data formats between instruments sending data and instruments receiving data. This situation led to the
development of an extension to the IEEE 488 standard. The new standard was published in 1987 and was

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