Communication interfaces — Automatic measurements

In a production plant, the exchange of data between several systems involved in controlling the smooth running of the whole has become a necessity.

Communications between computer systems (computers, microprocessors, etc.) and the technical environment to be monitored can present a multitude of configurations depending on many parameters:

• nature of the signal to be transmitted ;

• signal destination (storage, processing or control) ;

• distance, transmission frequency, etc.

Among these links, the most widely used are subject to standardization, defining a precise protocol for communications between these systems.

The purpose of this article is to study these links: series and parallel.

The serial link, as its name suggests, enables data to be transferred serially over a line linking two devices. In instrumentation, the RS 232C standard is the most widely used, and will occupy an important place in the remainder of this article.

The parallel link is designed for high transfer speeds over short distances between more than two devices. The automation of measurement chains has led to the creation of numerous standards, the most important of which is the IEEE-488 bus, analyzed in the second part of this article.

Each type of link is implemented using an interface card, making it easier to understand how serial and parallel interfaces correspond to links.