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.
RS-232 (Recommended Standard 232) was introduced in 1960 for serial communication transmission of data. Though still in use today, it's been replaced by other communication and networking standards like USB and Ethernet for most applications.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's 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 signals for the interface. However, the DE-9 was more common in the long run as all of the signals were rarely needed (Fig. 1). Dan R. dropped me a note about correcting the DB-9 reference to DE-9.
RS-232 Pins
The voltage level was initially ±24 V p-p and dropped to ±12 V p-p with EIA RS-232-C. The 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. This was fixed for most applications.
One application for RS-232 connections involved handling 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 9,600 baud with eight data bits, no parity, and one stop bit.
More RS-232 Articles
RS-232 remains an important tool which is why we have a lot of serial communication articles on Electronic Design including these.
Serial Communications 101
This eBook is a collection of Electronic Design articles covering different aspects of serial interfaces and protocols including RS-232.
