RS 232 SERIAL COMMUNICATION PROTOCOL SERIES
This will be particularly important later on with some of the discussion in this series of articles, where you can experiment with writing some of your own serial communication software. In addition to simply allowing a computer to communicate and transmit data to another computer, a null modem connection can be used to "simulate" the behavior of DCE equipment. In order to make this work you have to "cross" some of the wires so when you transmit some information on one end, the other computer is able to detect and receive that same information. Instead of going through the physical modems, they go through a "null modem", or a modem that really doesn't exist. Now imagine if these two computers are in the very same room. As explained earlier, this is a very common task, and in the 1980's and early 1990's it was common to have "Bulletin Board Systems" (BBS) where computers would call each other up with modems and exchange all sorts of information. One way to make this work is to connect the two computers to each other with a pair of modems. Unfortunately, when connecting two computers with a "straight" serial connection, the two computers are fighting each other on the same wires. Often you don't always want to connect a piece of equipment to a computer, but you would also like to connect two computers together. The reason this is called a "straight" connection is because when the cabling is put together, each wire on each end of the connection is connected to the same pin. There are many other similar kinds of devices, and RS-232 connections can be found on all kinds of equipment.
RS 232 SERIAL COMMUNICATION PROTOCOL PC
The PC that is used in a control room of the mill would be the Data Terminal Equipment. This would also be a form of what we now refer to as a piece of "Data Communication Equipment" that we would also want to be able to control remotely. In a more modern setting, imagine a piece of equipment in a very dangerous place, like in a steel processing mill that measures the temperature of the rollers or other steel processing equipment. This later gave way to other communication systems, but this was the beginning of the Internet. The typical connection speed was usually 50 baud or 110 baud, though very fast connections could reach 300 baud.Īs a side note, when the very first IMPs (Interconnection Message Processors) that formed the first nodes/routers of ARPAnet (the ancient predecessor of the Internet), this was exactly the connection system they were using. Years ago, when the use of timeshare computing systems was common, the user would dial a telephone, place the telephone's handset against an acoustical modem, and that modem would be connected to a simple dumb terminal with an RS-232 cable. Here, the modem can be thought of as the DCE and the terminal that faces a user is the DTE.
This is an instance where the subjects of modems and serial communication equipment have been mixed together. In practice, the distinction between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE) is simply a matter of function. In the world of serial communications, there are two different kinds of equipment: Early RS-232 connections were commonly used to connect terminal equipment to modems, so these topics are often intertwined.ĭata Terminal/Communications Equipment However, a fully implemented connection can contain as many as 25 wires. The simplest connection in common usage contains three wires: transmit (tx), receive (rx), and ground (gnd). At a minimum, an RS-232 connection may consist of a single wire connected between two pieces of equipment. This standard dates back to 1962 but has been substantially revised over the years to accommodate changes to communications technology. RS-232 is a standard for serial data communication between computing equipment.
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