TABLE OF CONTENTS The terms "data communications" and "networking" are often used interchangeably, but both refer to the transmission of data in digital form from one place to other places. The most important factors are that the source of the data and the receivers of that data use the same electrical technology to encode and decode the digital data, and that they share the same scheme for formatting the data. These are universal truths for all networks used for information technology (IT) and for industrial automation.
The earliest automation networks were not considered networks at all but, instead, serial "buses." The term fieldbus stems from this concept. Naturally, each network was designed to solve one problem, then extended to solve other, perhaps related, problems. Because each supplier's business model was directed toward a slightly different business niche, the resulting bus turned out to be different from any other.
As long as industrial automation networks were slow and uncomplicated, they required no special components. For example, EIA [1]-232, EIA-422/423, and EIA-485 were often used for the physical layers, supported by commodity semiconductors. Early protocols, data formatting, and error handling procedures were simple enough to execute on eight-bit microprocessors such as the 8051, Z80, or 6809. When speeds became higher and protocols richer in functionality, custom silicon became necessary to implement these networks. Custom silicon is expensive to design due to the nonrecurring engineering or NRE costs, and because the volumes are usually small compared with...
