I'm currently getting familiar with PLC's, the WAGO 750-8206 PLC in particular. It offers a linux OS and can run CoDeSys programs. There are some I/O modules attached to the controller: 750-530, 750-430 and 750-600. What I would like to know is this:
Is it possible to write a C++ linux application that runs on the PLC and gets/sets the digital inputs and outputs?
Even better: can I write a CoDeSys program that "talks to the I/O's" and handles all the logic and at the same time can be accessed by a C++ linux program? THe idea is this: I would like the CoDeSys program to check for let's say two digital inputs. If both are high, a variable should be set to a defined value. The linux application should be able to read that variable and conduct further processing (such as sending JSon data to a server or similar).
Also, I would need to be able to send commands from the linux application to the CoDeSys program in order to switch digital outputs (or set values on analog outputs etc) when the linux application receives a message that triggers the command.
Any thoughts and comments on this topic are greatly appreciated as I am completely new to this topic. Thanks in advance!
The answer you might want
The actual situation has changed into the opposite of the previous answer.
WAGO's recent Board Support Packages and Documentation actively support you in making changes and extensions to the PLC200 line. Specifically the WAGO 750-8206 and 17 (as of March 2016) other PLCs :
wago.us -> Products -> Components for Automation -> Modular WAGO-I/O-SYSTEM, IP 20 (750/753 Series)
What you have to do is get in touch with them and ask for their latest Board Support Package (BSP) for the PLC200 line.
I quote from the previous answer and mark the changes, my additions are in bold.
Synopsis
- Could you hack a PFC200 and get custom binaries executed?
Probably Absolutely yes. As long as the program is content to run on the Linux-3.6.11 kernel and glibc-2.16 and is compiled for the "armhf" API, any existing ARM application, provided you also copy the libraries it uses as well, will just run without even compiling it specifically for the PFC200.
- Would it be easy or quick?
No. Yes, if you have no fear of the Linux Command line. It is as easy as using the Cross Compiler provided by the Board Support Package (BSP) with the provided C-libraries and then run this to transfer your program to the PFC's flash and run it: scp your-program root@PFC200:/usr/bin
ssh root@FC200 /usr/bin/your-program
Of course, you can use Eclipse CDT with the Cross Toolchain for the PFC200 and configure Eclipse to do do remote run and debug.
- Will this change in the future?
Maybe. Remember that PFC200 is fairly new in North America.It has, PFC200 has appeared in September 2014
The public HOWTO Building FORTE for Wago describes how to use the initial BSP to run FORTE, which is the IEC 61499 run-time environment of 4DIAC (link: sf.net/projects/fordiac ), an open source PLC environment allowing to implement industrial control solutions in a vendor neutral way. 4DIAC implements IEC 61499 extending IEC 61131-3 with better support for controller to controller communication and dynamic reconfiguration.
In case you want to access the KBUS (which talks to the I/Os) directly, you have to know that currently only one application can be in charge of KBUS.
So either CODESYS, or FORTE, or your own KBUS application can be in charge of the KBUS.
The BSP from 2015 has many examples and demos how to use all the I/O of the PLC200 (KBUS, CAN, MODBUS, PROFIBUS as well as the Switches and LEDs on the PFC200 directly). Sources for the kernel and with all kernel drivers and the other Open Source components is provided and compiled in the Board Support Package (BSP).
But, the sources for the libraries and tools developed from scratch by WAGO and are not based on GPL/Open Source code are not provided: These include the Application Device Interface(ADI)/Device Abstraction Layer(DAL) libraries which do CANopen, PROFIBUS-Slave and KBus (which is used all PLC I/O modules connected to the main PLC unit)
While CANopen is using the standard Linux Socketcan API to talk to the kernel and you could just write a normal socketcan program using the provided libsocketcan, the KBus API is an WAGO-specific invention and there, you'd have to do some reverse-engineering if you'd not want to use WAGO's DAL for accessing all the electrical I/O of the PLC, but the DAL is documented and examples how to use it are provided in the BSP.
If you use CODESYS however, there is an "codesys_lib_demo-0.1" example library which shows how to provide a library for CODESYS to use.
Outdated Answer
This answer was very specific to circumstances in 2014 and 2015. As of 2016, it contains incorrect information. Still going to leave as-is for now to provide background.
The quick answer you probably don't want
You could very reasonably write code using Codesys that put together a JSON packet and sent it off to a server elsewhere. JSON is just text, and Codesys can manipulate text in a fashion very similar to C. And there are many ethernet protocols available from within Codesys using addon libraries provided by Wago.
Now the long Answers
First some background
Since you seem to be new to Wago and the philosophy of Codesys in general... a short history.
Codesys is used to build and deploy Hard Realtime execution environments, and it is important to understand that utilizing libraries without fully understanding the consequences can destabilize performance of the entire system (bringing Codesys to its knees and throwing watchdog errors in the program). Remember, many PLC's are controlling equipment that could kill someone if it ever crashed.
Wago is fond of using Linux to provide the preemptive RT kernel for the low level task scheduling and then configuring Codesys to utilize much of the standard C-libraries that often accompany linux. Wago has been doing this for quite some time, but they would never allow you to peel back the covers without going through Codesys (which means using IEC 61131 languages, of which C++ is not included), and this was for your own safety (and their product image). If you wanted the power of linux on a Wago, you had to get a special PLC with a completely naked OS, practically no manual or support, and forfeit the entire Codesys runtime.
The new PFC200's have much more RAM and memory available than recent models, allowing for more of the standard linux userland stack (ssh, ftp, http,...) to be included without compromising the Codesys runtime, and they advertise this. BUT... they are still keeping a lid on compilation tools and required header files needed to compile and link to Codesys libraries or access specialized hardware (the Wago KBUS, which interfaces your I/O modules).
The Synapsis
- Could you hack a PFC200 and get custom binaries executed? Probably yes.
- Would it be easy or quick? No.
- Will this change in the future? Maybe. Remember that PFC200 is fairly new in North America.
Things you may not know
Codesys does not necessarily know or care about Wago. You can get Target Platforms for Codesys that do target Intel processors running a linux os. Codesys DOES SUPPORT accessing external libraries (communication in the reverse direction is dangerous), but they often expect a C style interface, and you can only access those libraries by defining C-headers that Codesys will analyze, so you may need to do some magic to get C++ working seemlessly. What you can do is create a segment of shared memory that both C++ and Codesys access, and that is how they pass information (synchronization is another problem).
You can get an Open Wago PLC, running Codesys on Linux. Wago's IPC are made specifically for this purpose. They have more power, memory, and communication capabilities in general; but they do cost more than double your typical Wago PLC.
If you feel like toying with the idea of hacking a Wago, you will need to tear apart the manuals for Codesys (it has its own), the manuals for the Wago IPC's, and already be familiar with linux style inter-process-communication and/or dynamic libraries.
Also, there is an older Wago PLC that had the naked Linux on it 750-8??. It also has a very good manual on how to access the Wago hardware using supplied headers.
You must first understand how Codesys expects to talk to its target operating system. Then you work backwards to make it talk to Wago specific libraries living on that operating system. You must be careful not to hijack Codesys.
Your extra C++ libs should assist Codesys, not take it over. For instance, host a sqlite database on the same device, and use C++ to manage the database and provide a very simple interface that Codesys can utilize. All Codesys would do is call a function and pass some values, but your C++ would actually build an SQL query and issue it to the database (Codesys doesn't need to know why or how this is happening).
I hope at least one paragraph is helpful in some way.
