As the volume of data to transfer between systems increased and as more
data types other than just field inputs and outputs needed to be transmitted,
manufacturers sought a more robust approach to communication between systems.
Most computers had available built-in communication ports initially designed for
communicating to peripheral devices, such as printers or terminals, that could handle
different data types and fairly high volumes of data flow. Communicating between
systems by directly connecting a communication port of one system to that of a
second system became the obvious solution (Figure 17-2). Unfortunately, at this phase
in the development of software for computers, the programs to direct the dataflow
between systems typically had to undergo custom development for each application
and for each system. Developing custom communication software required specialized
knowledge and skills, which led to the creation of a new class of service providers
called automation systems integrators.
As process computers evolved into distributed control systems (DCS), more
sophisticated and intentional approaches to automation systems integration came
into play. DCS suppliers designed specific functional modules as gateways to
enable integration with other automation systems, such as PLCs, and intelligent
devices (Figure 17-3). These modules included (somewhat) preprogrammed basic
communication software in order to reduce the customization requirements and to aid
in the setup of these interfaces for communication with specific devices and systems.
Although these modules were easier to configure than the communication ports had
