What is RS232 cable?

RS232 cable is a kind of cable used for RS232 serial data transmission, but technically the cable used for RS232 data transmission should be DB9 cable. RS232 is more of a customary name, so RS232 cable and DB9 cable are the same kinds of cable. If you don't know what RS232 is, you probably still can't understand it, so I think you may need to understand what RS232 is first.

What exactly is RS232? First of all, it is a form of serial data transmission. Or simply put, it is a form of communication. Most people simply refer to it as a serial connection.

At one time, it was the most common form of data transfer. You may recognize the standard 9-pin DB9 cable. In short, an RS232 connection uses a positive voltage of binary 0 and a negative voltage of binary 1 to transmit signals. But what is the use of RS232 for PLCs?

PLCs use RS232 to communicate with other modules and even other PLCs. These modules can also use RS232, such as an operator interface or HMI, a computer, a motor controller or drive, a robot, or some sort of vision system.

One important thing to remember when using an RS232 device is that there are two different types.

DTE stands for Data Terminal Equipment. A common example is a computer.

DCE stands for Data Communication Equipment. An example of a DCE is a modem.

The reason this is important is that two DTE or two DCE devices cannot communicate with each other without some help. This is usually done using a reverse (zero modems) RS232 cable connection to connect the devices.

Usually, our PLC is the DTE, and the device we use is the DCE, and everything should communicate.

A very common example that many of you may be familiar with is a computer connected to a printer. While USB has become the standard, RS232 is still widely used for older printers in the workplace.

The RS232 protocol and cable allow the computer to send commands to the printer via voltage signals. The printer then decrypts these commands and completes the print.

Disadvantages of RS232.

One is the speed of data transfer. The data transfer rate is about 20 KB per second. This is quite slow compared to what people are used to today.

Another problem with RS232 is that the maximum length of the cable is about 50 feet. Wire resistance and voltage drop can be a problem for longer cables than that. This is one of the reasons RS232 is not as widely used for remote installations as the newer technologies.

For many years, RS232 has been the industry standard. Today, USB and Ethernet have begun to phase out this older serial communication standard. However, with the help of simple adapters, devices can still communicate with each other using the old and new standards. Many manufacturers still use RS232 because it has always been common and inexpensive.

Manufacturers can use RS232 to connect PLCs to devices such as HMIs, input and output modules, and motor drives, just to name a few. Remember that RS232 is only one form of serial communication or a way to transfer data. A standard DB9 cable is probably the most common cable used in this application.

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