What is RS232 and What is it Used for?

What is RS232 and What is it Used for?


Today you will learn about RS 232. 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. Before we get into today’s
video, if you love our videos, be sure to click the like button below, and make sure to click
subscribe and the bell to receive notifications
of new RealPars videos. This way you never miss another one! What exactly is RS-232?
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, RS-232 transmits signals using a positive voltage for a binary 0 and a negative voltage for a binary 1. But what do the PLCs
use rs-232 for? PLCs use RS 232 to talk to other
modules or even other PLCs. These modules can be anything
that also uses RS 232 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 RS 232 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 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, RS 232 is still widely used for
older printers in the workplace. The RS 232 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 RS-232. 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 RS-232 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 RS-232 is not used as much
as newer technology for remote installations. So let’s review what we have learned. For years, RS-232 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 RS-232 since it has always been
widespread and inexpensive. Manufacturers may us RS-232 to
connect PLCs to devices like HMIs, input and output modules, and
motor drives, just to name a few. Keep in mind that RS-232 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 RS-232 is used for. Check back soon for
more RealPars videos! Make sure that you head
over to realpars.com. To find even more training material
for all of your PLC Programing needs.

Danny Hutson

54 thoughts on “What is RS232 and What is it Used for?

  1. Thanks for letting us know about it. Now including RS485, I now know what RS232 cable is and its disadvantages.RealPars is the place to learn automation and not just programing PLCs.

  2. Thanks a lot for this explanation, but i think that the RS232 is a point to point network, wich you can connect only 2 devices, that's why the RS422 and RS485 came after that and allows the multipoint connection, is that correct ?
    and it's the physical support used also in the Serial Modbus and ProfiBus network.

  3. SIR
    Yr video "RS232"

    Wached yr above video and I LIKED IT. I find it is useful to know.
    Positive features of yr video are:–
    1 Excellent video production (technically) and presentation.
    2. You spoke in OXFORD ENGLISH , distinct / clear pronounciation and clearly audible.
    3. Precise compact information presented to make the viewer understand clearly.
    4. Lastly yr summarising what all you explained earlier/ all the while helps memorising key important points.
    Vatsa INDIA.

  4. you completely left out rs232 did NOT start out as a db9 but a db25 just like a parallel connection. not only that, in the beginning they both had female connectors on the back of both pc compatibles and cp/m computers. also 2 computers connected with a crossover or null modem cable can actually be considered a peer to peer network. it may have been slow, but it was much easier than transferring files with floppies by a long shot. if you actually want to learn something then google laplink. if i really want to date myself, i can tell you how i communicated with a mainframe, using a serial modem, a dumb terminal over a straight thru 25 pin serial cable at half duplex. that is why serial is so slow, because it is at half duplex, meaning you could either send or receive data but not do both like a full duplex ethernet connection. do you even know what the anacronym modem stands for? it is modulate demodulate, meaning my modem takes digital information, turns it into an audible tone that gets sent over a phone line, then your modem hears it, turns it back into digital information and sends it to the computer. i always laugh myself silly when children like you try to explain computer history and completely screw it up. next time do your homework.

  5. RS232 in the real world is full of nasty surprises though. A lot of equipment isn't entirely compliant.
    – The correct voltage levels are +-12V, which is great for driving long cables. But it's also difficult (ie, expensive) to generate electrically from the supplies typically available in equipment, so corners are sometimes cut and the voltage reduced. +-5V is so much easier to make, it's just a cheap charge pump, and most equipment is fine with it over short cables. But then you happen to have that one piece of equipment that isn't, or a long cable, and the connection doesn't work – for reasons you won't be able to identify without electrical test equipment.
    – USB-to-RS232 adapters often skip out lines like flow control, RI and DCD. Again, to save money, because most equipment doesn't need these lines. So who will notice? Until someone does. So you end up with adapters that seem to work, pass any test, work on most equipment – but then you start on certain devices, and they fail. Worse, those flow control lines only get used under substantial data transfer – so the link may appear to pass every test, you may even be able to use it to configure your device without any problems, giving the impression that all is well and your serial link is fine – then you send a page full of text to print or a long string of g-code commands and they end up corrupted.
    – There's no autoconfiguration. You need to get every setting right – bit rate, parity, start and stop bits, byte length, flow control method. A misconfiguration of length or flow control again may appear to work when testing, but then fail when sending the intended data through.

    With RS232, you really need to know everything there is about how it works in order to recognise and diagnose problems. There's a reason USB replaced it, and it's not just because USB is faster.

  6. Hi, awesome video , I need some help though.

    Can you convert a rs232 to ethernet and the back to rs232 with a adaptor?
    And would the a PLC still be able to understand the data and continue to send and receive data?

    Thanks

  7. Is it possible to connect two or more devices in a parallel connection to a single UART channel for both Rx and TX

  8. Omg I ran so many RS-232 cables throughout a building for terminals. Back in the day RS-232 was on a DB25 using full hardware handshake. Also 20ma current loop was used for long hauls. Originally used to replace telegraphy equipment along the railroad. Western union used it for telegrams on Teletype equipment.
    Dont be fooled just by DB9 connectors as RS-232 was originally DB-25 (25 pin connectors)

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