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KNOW THE LINGO — WHAT IS RS232?

By: , CTS-D
Technology Evangelist — C2G

Technical lingo is a kind of shorthand that's used to express concepts common to that specific topic or area of study. Technical lingo is important because it provides a very precise or unique "shorthand" description of a device, effect or concept. Unfortunately, if you aren't comfortable and familiar with the lingo of a topic it can be a tall hurdle to communicate efficiently with folks who consider the jargon of their field to be "self-explanatory." In this series of articles we'll lift the veils of misunderstanding from the lingo of the A/V industry.

WHAT IS RS232?

In 1997 the Telecommunications Industry Association (TIA) issued TIA-232-F, the standard that describes what RS232 is and does in contemporary electronics; however, RS232 is much older than this. The basic outline was first released by the Electronics Industry of America (EIA) in 1962 and was intended to define the communication between an electromechanical typewriter and a data circuit terminating point (called a DCE; essentially this is a modem). This was the beginning of teletype!

The Electronic Industries Alliance (EIA; until 1997 Electronic Industries Association) was a standards and trade organization composed as an alliance of trade associations for electronics manufacturers in the United States. They developed standards to ensure the equipment of different manufacturers was compatible and interchangeable. The "RS" in RS232 stands for "recommended standard" and was published by the Radio Sector of the EIA.

By the mid 1980's and into the 1990's, RS232 was a common port on most computers, where it was used to connect printers and other peripherals. The RS232 serial port, which uses either a DB25 (D-subminiature 25-pin connection, an older implementation) or DB9 connector, operates at voltage levels of 5 to 15 volts. Because RS232 uses such high voltages, its use on computers was supplanted with USB connectivity and RS232 is rarely found on computers today. Many industry experts believe that RS232 use will gradually decline as structured USB connectivity becomes even more prevalent.

RS232 is a serial system and therefore data is sent one bit after another, as there is only one data line in each direction. Data on RS232 is normally sent using ASCII (American Standard Code for Information Interchange).

Transmissions using RS232 are limited in speed and link length. Maximum data rates are typically 19,000 baud (19.2 KBd). This is roughly 20Kbps. Compare this speed with USB 2.0 at 480Mbps and you will see that USB 2.0 is capable of communicating about twenty thousand times faster. RS232 link lengths are limited to about 15 meters—although for even slower transmission speeds longer lengths can sometimes be used. With these longer lengths, care must be taken because RFI/EMI becomes a problem. This can result in the data becoming corrupted, even when slow transmission speeds are used.

Today RS232 connectivity is used as a method of controlling remote devices by computers and data recorders. RS232 has become a bona fide industry standard, and it is used in a host of applications that were never conceived when it was first launched in 1962. It is ideal for applications where it is necessary to send data over a straightforward set of cables, as RS232 at its most basic only requires three conductors. RS232 is often used to control displays and projectors, automated screens and masking systems, lighting and heating controls, and various sensors and other devices. For that reason RS232 functionality is an important feature included in the HDBaseT system standard as well as many control products, such as the A/V Controller.

This white paper is for informational purposes only and is subject to change without notice. C2G makes no guarantees, either expressed or implied, concerning the accuracy, completeness or reliability of the information found in this document.