Jakob Sagatowski's Posts

PLCopen has released their coding guidelines for 61131-3 structured text (ST) some time ago. If you haven’t read that yet, I highly recommend you to do so! Even if I don’t agree with everything, it’s still a good read and a really good initiative to consolidate all the different coding guidelines that every vendor has for their 61131-3 ST environment.

Included in this is Rule L16 “Define the use of tabs”. Let me quote:

Use of tab character (ASCII code 9) should be avoided, and Programming Support Environment set to replace tabs with spaces

This is a common rule in many projects, as this simplifies copying of code into other contexts and makes the code less dependent on the user settings for display. Simply put, the visual interpretation of a tab character varies wildly. As the TwinCAT development environment integrates into visual studio, this is the place we need to do our change. I’m going to use visual studio 2015 community edition for this particular demonstration, but it should be more or less the same in the other versions of visual studio.

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When integrating various forms of devices, generally speaking there are usually requirements that a certain degree of fault isolation of those devices needs to be done. EtherCAT slaves specifically can transmit emergency objects (EMCY) – a protocol inherited from CANopen. An emergency message is a high priority message sent once, and is triggered by an error event in the EtherCAT slave device.

Normally the emergency objects are showing up in the visual studio development environment, but that might not be enough. At one occasion I wanted to be able to handle the emergency objects in PLC code. Handling and reception of the emergency objects via the diagnosis history object will be explained in two parts – first we’re going to start with the theory of the diagnosis history object. In the second part we’ll create function blocks to implement handling of the diagnosis history object. The first part is out and can be located here!

Warning Icon by Martz90 / CC BY

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When I develop software I mostly do the testing on my development computer. It is after all one of the big strengths of being able to run your code on a PC platform – it should more or less work the same on a PC based PLC. But then there is only so much testing you can do in your development machine, at some point you still end up needing to have the real hardware. I’ve already ended up with having some EtherCAT-slaves connected to the development computer so I decided I’ll go for a PLC to split the development computer and run-time environment completely. As Beckhoff has released PLCs from their embedded line with Windows 10 IoT Enterprise LTSB I though that was another reason good enough to buy one and experiment with it. Ended up with a CX5140 with 4gb of RAM and 32GB of flash-storage. Works like a charm out of the box, and I’ve already noticed some changes compared with running a controller with Windows 7 embedded. Since Windows 8 embedded, Microsoft have apparently replaced the FBWF (File-Based Write Filter) with the new UWF (Unified Write Filter). I’ll continue running/testing all my code on this controller, and will be posting new content to this blog as often as I can.

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3S-Smart Software Solutions has since pretty long had a Raspberry Pi (RPI) target image available for their CODESYS runtime. The intention was to create something that you could buy very cheap, primarily for students and such to learn how to program 61131-3.

As I’m primarily working with TwinCAT3, which is based on CODESYS, I’ve been thinking about building a really cheap 61131-3 compatible PLC based on the RPI and the CODESYS target. I didn’t just want it to be one board laying around in my home, but I also wanted it to have the “industrial” feeling, and luckily I found a perfect development board + case for me to initialize the project. Now that it’s finished, I have a PLC running an EtherCAT master in the CODESYS runtime for almost no money at all.

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Webpage is up! Here I’m going to have various information about different PLC programming tutorials. This will mostly be in the TwinCAT 3 and CODESYS environment. I’ve found out that there aren’t too many blogs/resources on TwinCAT 3 development. As I’m working with mostly TwinCAT-development every day at my job I thought it would be a good idea to share some of the knowledge I’ve aquired during as time has passed. Stay tuned!

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