Free PLC programming software question

I'm no lawyer by any means. I was wondering if there would be any legal ramifications (ie justifiable means of getting sued) by writing an Open Source PLC programming software package. Let's use AB SLCs and RSLogix 500 as an example (only because I'm familiar with them - freely replace with Vendor X). Specifically, AB doesn't release any specs for how programming software communicates to devices. This would undoubtedly require extensive work with a packet sniffer. I don't think you would need to reverse engineer RSLogix itself - only be familiar with what the program does.

So take this fantasy a bit farther. If such a mature project opens up on sourceforge, could AB shut them down or legitimately threaten with litigation?

This is merely a curiosity, prompted by this post.

Not sure... but I know that there are some 'after market' programming packages for other PLC's (ie S5 and S7 for Windows) I am sure that Siemens knows about it... but they let them market and sell it ?? why know one jumped on AB's I don't know??

The really, really old AB documentation had all you needed to write your own software. I'm talking PLC2 era here, though. I don't know that the PLC interface has changed much, but it could have.

I alwys thought the info was "out there", as there have been other software vendors for AB up until recently.

I think this would be very tough to accomplish without insider knowledge (code). Plus a simple firmware update could potentially invalidate all the effort.

OG

I'm not a lawyer so take this for what it's worth. I don't think there is anything they can do about that particular scenario. You haven't copied any code or tried to decompile it. You are simply listening to communications. I don't think there is anything particularly illegal about that.

As for AB specifically I think you would be going at the wrong audience. Generally, people whose choice of plc is influenced by free software won't be too inclined to drop $4,000 on a plc in the first place. People buying AB in the first place will just take the hit on the software too. That is probably why RSLogix hasn't been 'emulated' yet. People looking for free software will be looking for a less expensive PLC. But I digress.

Keith

Keith

I also dont think there can be anything illegal about it. And I also do not think you can be held liable for consequenses if your software is buggy. You just have to state the same kind of disclaimers as the big guys do.

I know of several 3rd party programming softwares for S5 and S7, and one for AB PLC-2.

Thinking about it a little more, I would actually want a project like that if I was AB. You're right, at that price range I doubt it would cut into their sales. It adds the benefit of a community of geeks toying with the innards. You really wouldn't want a buggy, crappy app making your product look bad - but you wouldn't want a better product than your own. That's not a fine line, though.

kamenges said:

You haven't copied any code or tried to decompile it. You are simply listening to communications. I don't think there is anything particularly illegal about that.

As for AB specifically I think you would be going at the wrong audience. Generally, people whose choice of plc is influenced by free software won't be too inclined to drop $4,000 on a plc in the first place. People buying AB in the first place will just take the hit on the software too. That is probably why RSLogix hasn't been 'emulated' yet. People looking for free software will be looking for a less expensive PLC. But I digress.

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Operaghost - I doubt they have that kind of security/flexibility built in. Updates like that would hurt their backward compatibility far more than a little free programming software project. I'm willing to bet the communication isn't that complex - each ladder rung is broken down into a simple text string.

Maybe I'll sponsor such a project after I win the lotto. I don't have the: time, skillset, or inclination, to do so now. So the project will remain an interesting thought...

Unless people want to run it on linux don't think your going to see a whole lot of interest from the opensource community. I have one laptop with Windows XP pro installed just for these type applications.

At one time, there was a 3rd party vendor of AB software. I believe that it was called WinLogix. Then RA decided it was a much better product then what they had and they purchased the company.


Isn't this whole idea called free enterprise?

An additional possible analogy, all the 3rd party vendors writing software to run on PC hardware (ok, or Apple). No vendors go after the 3rd party (as long as they are not treading on patents).

There actually was an open source Allan Bradley simulator available. It was called "Classic Ladder". It would turn your PC into an AB simulator. It also had a driver to let you hook up the parallel port as an IO device so you could make a cheap, dirty and small soft PLC.
It may still be out there. If so, you may be able to adapt it to your needs.
I know that this is not quite what you asked, but it could be a starting point.

is this it:
http://membres.lycos.fr/mavati/classicladder/

Yeah, you'd think so. But the practice turned out to only work with a copywright/patent system, which contradicts the system to some extent. Then introduce lawyers to the scene...

Oakley said:

Isn't this whole idea called free enterprise?

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You don't think people would rather use a free programming app than a $4000 one? I've seen lots of posts here recently asking for that.

wirepuller134 said:

Unless people want to run it on linux don't think your going to see a whole lot of interest from the opensource community. I have one laptop with Windows XP pro installed just for these type applications.

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Yeah, everybody wants "free". You know, though, that with RSLogix there's not much need to have to call the help desk for program errors, PLC issues, etc. That's why they charge for it, I guess. There's an amazing amount of documentation available, and now it's really good.

For a "free" product, you would want a help desk, reference material, someone to answer why, at midnight on Dec 31st, your program wiped and took the C drive with it...

I LIKE free. I don't think you could expect the normal AB quality in free software, though.

i think you could (and would!) if the interface portion of the hardware/software/protocols was open book instead of something propriatory.

i don't mind $4000 for sofware once in a while but if i have to pay that much for something, i really don't want to wrestle with it, at this price this better be something well rounded and user friendly.

Sure - That's why I concluded that AB wouldn't lose much of their $4000 market. They provide a good product and people pay for it. For many applications it's more than worth the money.

I don't understand why everyone's underlying assumption is that a competing product would have to be ****. I think a 3rd party vendor could produce a superior product and sell it for much less. "Free" doesn't equate to **** - this "you get what you pay for" mentality isn't as applicable to software where the cost to redistribute it is zero. Do you worry about calling a help desk for Mozilla Firefox. I find it to be the best product in the industry.

While I deliberately used AB as an example because RSLogix is a decent program, I could hardly agree with the "normal AB quality" portion of your statement. AB hardware is ironclad, their software is fine, but nothing to write home about. Just because most industrial Open Source projects are stuck in early Alpha/Beta phases, doesn't mean that AB software is any better or that another project couldn't be. Besides, I think the reason forums like this are so popular is because of the quality of helpdesks like that.

tomalbright said:

Yeah, everybody wants "free". You know, though, that with RSLogix there's not much need to have to call the help desk for program errors, PLC issues, etc. That's why they charge for it, I guess. There's an amazing amount of documentation available, and now it's really good.

For a "free" product, you would want a help desk, reference material, someone to answer why, at midnight on Dec 31st, your program wiped and took the C drive with it...

I LIKE free. I don't think you could expect the normal AB quality in free software, though.

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