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What is RS232 and what is it used for?

Today you will learn about RS232. It is a phrase you may hear fairly regularly in industry, especially by the older guys. Hopefully, this blog post/video will clear some things up for you.

Today you will learn about RS232. It is a phrase you may hear fairly regularly in industry, especially by the older guys. Hopefully this video will clear some things up for you.

What exactly is RS232? First and foremost, it is a form of serial data transmission. Or simply put, it is a form of communication. Most people simply called it a serial connection.

At one time, it was the most used form of data transmission. You will probably recognize the standard 9 pin DB9 cable. Simply put, RS232 transmits signals using a positive voltage for a binary 0 and a negative voltage for a binary 1. But what do the PLCs use RS232 for?

PLCs use RS232 to talk to other modules or even other PLCs. These modules can be anything that also uses RS232 such as, operator interface or HMI, computers, motor controllers or drives, a robot, or some kind of vision system.

One important thing to remember if you find yourself using RS232 devices is that there are actually two different types.

DTE stands for Data Terminal Equipment. A common example of this is a computer.
DCE stands for Data Communications Equipment. An example of DCE is a modem.

The reason this is important is because two DTE or two DCE devices cannot talk to each other without some help. This is typically done by using a reverse (null-modem) cable to connect the devices.

Typically our PLCs will be DTE and our devices used will be DCE and everything should talk to each other.

One very common example that many people are probably 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 give commands to the printer via a voltage signal. The printer then deciphers those commands and completes the print.

There are a couple of disadvantages of RS232.

One is the speed at which data can be transferred. Data can be transferred at around 20 kilobytes per second. That is pretty slow compared to what people are used to now.

Another issue with RS232 is that the maximum length a cable is about 50 feet. Wire resistance and voltage drops become an issue with cables longer than this. This is one reason RS232 is not used as much as newer technology for remote installations.

So let’s review what we have learned. For years, RS232 has been a standard in industry. Today, USB and Ethernet have started to phase out this older serial communication standard.

However, with the help of simple adapters, devices can still talk to each other using the new and old standards.

There are still many manufacturers using RS232 since it has always been widespread and inexpensive.

Manufacturers may use RS232 to connect PLCs to devices like HMIs, input and output modules, and motor drives, just to name a few.

Keep in mind that RS232 is simply a form of serial communications, or a way to transmit data. A standard DB9 cable is probably the most used cable for this application.

I hope this has been helpful in understanding just what RS232 is used for. Check back soon for more RealPars blog post!

With so much love and excitement,

The RealPars Team

By Kevin Cope

By Kevin Cope

Instrument Mechanic

Posted on Sep 17, 2018

By Kevin Cope

Instrument Mechanic

Posted on Sep 17, 2018

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