RS-232 (Recommended Standard 232) was introduced in 1960 for serial communication transmission of data. It is still in use today but it has been replaced by other communication and networking standards like USB and Ethernet for most applications. RS-232 connectors were ubiquitous on IBM PC-compatible systems and many commercial and industrial systems in the past. It is just one of many serial standards.
Here are some interesting facts, articles and podcasts about RS-232. Take our RS-232 poll if you get a chance.
The standard connector was a DB-25 that supported all the signals for the interface but the DB-9 was more common in the long run as all the signals were rarely needed (Fig. 1).
RS-232 Pins
The voltage level was initially ±24 VPP and dropped to ±12 VPP with EIA RS-232-C. There serial protocol could vary and usually included a start bit, data bits (typically 7 or 8), an optional parity bit and one or more stop bits. The baud rate and serial encoding had to be set at both ends to operate properly. For most applications this was fixed.
One application for RS-232 connections were to handle acoustic modems. Many of these implemented baud rate recognition by expecting an initial handshake character and tracking the bit duration. Other techniques were used as well. A typical connection was 9600 baud with eight data bits, no parity and one stop bit.
Control Design Podcast: The legacy and evolution of RS-232
In this episode of Control Intelligence, editor-in-chief of Control Design, Mike Bacidore, explains the history of RS-232 and its role in industrial manufacturing.
More RS-232 Articles
Serial Communications 101
This ebook is a collection of Electronic Design articles cover different aspects of serial interfaces and protocol including RS-232.
