Before you start learning to code programmable logic controllers, you need to get the software meant for coding. They haven’t changed much throughout the years, so the only changes will be minor ones. Some details will be added to older versions, but all of them have the explanation when you click on them. There are many sites you can download the program from.

PLC programming can be difficult at the start if you don’t have someone to work with you, but if someone else managed it you can also. Also, there are sites that offer you support if you have any problem with PLC or PLC software. There are a lot of little things to remember when it comes to coding, but with some professional help, it will go fast.

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Starting a project

When you open the software you will start with the start screen, and you can close that off, or if you want you can click on view in the main menu and then click start screen again. In the main toolbar, you will notice your online and offline menus.

To start a new project you have to click on the file in the main menu, then a new project, and online. Next step is to give a name to the project and hit okay. That will automatically bring up your screens, and you will see there is a terminal, run, and stop. You need to make sure that is terminal, so the designer software will actually run your terminal software.

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When you click on edit mode in the main toolbar it will allow you to edit the ladder diagram. The menu with all the instruction available will pop up, and you also can see what every instruction does. In the bottom, you will have some main instructions that are going to be used as shortcuts, and you normally start with normally open contact.

That normally open contact is the input and on the other end, you should set the output that is placed also at the bottom menu with other instructions. You are also going to name them, for example, X0 for input and Y0 for output. Once you save it, you can actually turn on the input and you will notice that the output doesn’t turn on, that is because you are not in run mode or program mode.

Steps in program development

The first step before you start programming is to define the task. When you have a machine that you have to program your PLC for, you need to figure out what is actually going to happen. There is usually a master switch that starts the process and shuts it down. Then you need to check for sensors and switches.

Once you have defined the task you need to define the inputs and outputs. The third part is to develop the logical sequence of operation. You can use a flowchart or sequence table, and what this allows you to do is to fully understand the logic before you start programming it. By doing this step you can eliminate a lot of time and aggravation trying to figure out the logic itself. Read more on this page.

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After you finish these three, you can finally develop the PLC program. So, when you start programming it will be easier when you know how the machine is functioning, and you will have the steps in your head that you will use for coding, so you will develop the ladder much quicker. The most important part of the ladder development is documentation.

The final step is testing the program. You want to test it thoroughly to make sure that it actually works. After a while when the testing is done, you want to go back to the operators after a couple of months and ask them if that is exactly what they want. That is when you can make some modifications based on operator feedback.

Binary interpretation

One or zero is the only thing that the computer understands, but that is actually referred for inputs and outputs of your PLC, so it is on or off. If you look at the PLC addresses, you can use binary coded decimal, hexadecimal, or ASCII meaning American standard code for information interchange.

The binary terminology is bit one or zero. Four bits are called nibble, or a digit, eight bits are two nibbles or a byte. Sixteen bits are 2 bytes but also 1 word. This also depends on which processor you are using.

ASCII is based upon 8 bits or 2 hex, and it really represents everything that you can display on a keyboard. So, every letter on a keyboard has its own number in the binary system. On the ASCII site, you can see the codes table, and it shows all the different things you can have on your keyboard. So, every time you hit a key it sends bits of information out to the computer.

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Under the tools menu, you will find four different things you can do for documentation. You have a documentation editor, assigned nicknames, common editor and title page editor. For starters, you are going to do the document editor. There you will add exactly what it is, nickname, extra information, and description for your inputs and outputs.

Under tools, you want to go to the comment editor. It allows you to go rung by rung and document exactly what that rung is doing in your program. Remember that every program should be read like a book. You will notice that this tool is very useful to actually document and ensure that your reader understands exactly what is going on in the program. It is important in the PLC that you understand that everything is “make before break”.

If you get stuck coding, it isn’t anything new to look at someone’s work and copy what they were doing. It is much easier to look at comments and adapt already made code for your PLC program.