The "232" is just a number, like the "17" on the front of the bus I get into town.

Here's what Wikipedia has to say about the standard.

You could always check IEEE for their answer to RS-232 ... since it is their area of expertise.

http://www.ieee.org/portal/site or http://www.answers.com/topic/rs-232

Originally the whole name had an explanation such as Recieve Send - 2 3 2 ... or pin 2 to 3 and 3 to 2.

Pulled from Answers link above on rs232 pinouts:

25 pin
1 - PG Protective ground
2 - TD Transmitted data

3 - RD Received data
4 - RTS Request to send

Basically it is a short form reminder for a cabling requirement, pin 2 to 3 and 3 to 2.

"Originally the whole name had an explanation such as Recieve Send - 2 3 2 ... or pin 2 to 3 and 3 to 2."

D'you have anything to support that? How about RS422, 423, 485 etc.?

IMHO, that's serendipity.

All the cool kids are calling it EIA/TIA-232 these days. 232 is just the number of the standard. A quick google search will tell you all you ever need to know about it.

Hello everyone,

I always wondering, If MODBUS, PROFIBUS and TCP/IP are communication protocols and Optical fiber, ethernet are hardware media for data transmission for the protocols what does RS232 or RS 485 stand for. Are they communication protocols or transmission media?

Because i read it some where that RS232 carries voltage and RS485 carries current signals, if so for a communication link of RS485 what can be the communication protocol

Sorry i seem to be a layman..............

Guest,

It can be confusing, until you sort out the jobs each of these do. RS-232, RS-485, etc. all specify the physical connection rules (how many can use the link, how to tell when to send and when to receive, etc.). MODBUS, PROFIBUS, etc. specify the way in which the data is packaged to go over this connection. Another specification is the connection speed (baud rate) and the number of data and stop bits in each word of data. Then you have to consider the program or software that is generating and using the data--it must be intelligible to the program.

I have named four layers in the communication. They are sort of like taking a trip in a taxicab. You have the road, the vehicle, the driver, the passengers, and the fare payment. Think of the physical wiring as the road, the RS-232 etc. as the vehicle, the speed and bits as the driver, the data being sent using MODBUS etc. as the passengers, and the software as the fare payment. All contribute to the finished job--communication--but in different ways. (I hope no one will jump too hard on the portions of this analogy that don't fit too well.)

--JMM

RS-232 - History

This standard was originally used for specifying the connection between an electromechanical teletypewriter and a modem. When electronic terminals (smart and dumb) began to be used, they were often designed to be interchangeable with teletypes, and so supported RS-232. The C revision of the standard was issued in 1969 in part to accommodate the electrical characteristics of these devices.

Since application to such devices as computers, printers, digitizer tables, test instruments, and so on were not envisioned in the standard, designers implementing an RS-232 compatible interface on their equipment often interpreted the requirements idiosyncratically. Common problems were non-standard pin assignment of circuits on connectors, and incorrect or missing control signals. The lack of adherence to the standards produced a thriving industry of breakout boxes, patch boxes, test equipment, books, and other aids for the connection of disparate equipment.

Later personal computers (and other devices) started to make use of the standard so that they could connect to existing equipment. For many years, a RS-232-compatible port was a standard feature for serial communications, such as modem connections, on many computers. It remained in widespread use into the late 1990s and while it has largely been supplanted by other interface standards in computer products, it is still used on legacy equipment.

One exception is mainframe computers. These large systems generally have specialized I/O processors for communication with terminals. For instance, some IBM mainframes had a Telecommunication Control Unit (TCU) attached to their multiplexer channel. The TCU would support multiple terminals, sometimes up to hundreds. Many of these TCUs could support RS-232 when it was required, although usually there were other serial interfaces.

The standard has been renamed several times during its history as the sponsoring organization changed its name, and has been variously known as EIA RS 232, EIA 232, and most recently as TIA 232. The standard continues to be revised and updated by the EIA and since 1988 the Telecommunications Industry Association (TIA[2]). Revision C was issued in a document dated August 1969. Revision D was issued in 1986. The current revision is TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange, issued in 1997. Changes since Revision C have been in timing and details intended to improve harmonization with the CCITT standard V.24, but equipment built to the current standard will interoperate with older versions.

Source: http://www.experiencefestival.com/a/RS-232_-_History/id/4697245