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rathersimplebecauseofthelimitedcomputingpowerofthedevicesavailableatthattime.Ofcourse,
these communication systems have a point-to-point nature and therefore lack the multidrop charac-
teristic of modern fieldbus systems, but nevertheless they were the origin of serial data transmission.
Talking about serial data communication, one should notice that the engineers who defined the first
protocols often had a different understanding of the expressions “serial” and “parallel” than we have
today. For example, the serial Interface V. transmits the application data serially, but the control
data in a parallel way over separate control lines.
In parallel to the development of data transmission in the telecommunication sector, hardware
engineers defined interfaces for standalone computer systems to connect peripheral devices such as
printers. The basic idea of having standardized interfaces for external devices was soon extended
to process control and instrumentation equipment. The particular problems to be solved were the
synchronization of spatially distributed measurement devices and the collection of measurement data
from multiple devices in large-scale experimental setups. This led to the development of standards
like computer automated measurement and control (CAMAC, mainly used in nuclear science) and
general purpose interface bus (GPIB, later also known as IEEE ). To account for the limited data-
processing speed and real-time requirements for synchronization, these bus systems had parallel data
and control lines, which is also not characteristic for fieldbus systems. However, they were using the
typical multidrop structure.
Later on, with higher integration density of integrated circuits and thus increased functionality
and processing capability of microcontrollers, devices became smaller and portable. he connectors
of parallel bus systems were now too big and clumsy, and alternatives were sought []. he underlying
idea of developments like I
C [] was to extend the already existing serial point-to-point connections
of computer peripherals (based on the RS ) to support longer distances and finally also multidrop
arrangements. he capability of having a bus structure with more than just two connections together
with an increased noise immunity due to differential signal coding eventually made the RS a
cornerstone of fieldbus technology up to the present day.
Historically the youngest root of fieldbus systems, but certainly the one that left the deepest mark
was the influence of computer science. Its actual contribution was a structured approach to the design
of high-level communication systems, contrary to the mostly monolithic design approaches that had
been sufficient until then. his change in methodology had been necessitated by the growing number
of computers used worldwide and the resulting complexity of communication networks. Conven-
tional telephone networks were no longer sufficient to satisfy the interconnection requirements of
modern computer systems. As a consequence, the big communication backbones of the national
telephone companies gradually changed from analog to digital systems. his opened the possibility to
transfer large amounts of data from one point to another. Together with an improved physical layer,
the first really powerful data transmission protocols for WANs were defined, such as X. (packet
switching) or SS (common channel signaling). In parallel to this evolution on the telecommuni-
cations sector, LANs were devised for the local interconnection of computers, which soon led to
a multitude of solutions. It took nearly a decade until Ethernet and TCP/IP (transmission control
protocol/Internet protocol) finally gained the dominating position they have today.
20.3.2 Evolution of Fieldbusses
The preceding section gave only a very superficial overview of the roots of networking, which not
only laid the foundations of modern computer networks, but also of those on the field level. But let us
now look more closely at the actual evolution of the fieldbus systems. Here again, we have to consider
the different influences of computer science and electrical engineering. First and foremost, the key
contribution undoubtedly came from the networking of computer systems, when the ISO/OSI (open
systems interconnection) model was introduced [,]. [,].This seven-layer reference model was (and
still is) the starting point for the development of many complex communication protocols.
