Dear Automation List: I'm not singling out Mr Rodriguez here, but we are asked this message multiple times a week, mostly for Modbus, as well as other PLCs. This makes it a prime candidate for a FAQ, but we need to answer the question. Does anyone know of a good resource on the web for getting communications components, source code, or what have you for various brands of PLCs. I'm thinking of a site with links to the documents containing the protocols, links to companies selling OPC servers and COM components talking to PLCs, and links or complete source code to talking to PLCs. This link could be sent out in a message to those subscribing to the automation list, and it would make everyone happy! This would seem to me to be a useful resource. Does anyone know of any site like this? If not, what does one think about creating a site like this?
Regards to all
Alex Pavloff
Software Engineer
Eason Technology
> -----Original Message-----
> From: "Cristian Rodriguez S." <[email protected]>
> To: 'Automation List' <[email protected]> > Subject: COMM: Modbus code
>
> I am looking for some code or software for connecting an > application in VC++ > that generate 15 different outputs ( Integer values each one) > with a PLC, and > this PLC use MODBUS communication protocol. My original idea > is create a > code for communication but I need some person to orient me. > If is possible for your help I appreciate this. > > Thanks for your help in this issue > > Atte. > Cristian Rodriguez Silva.

 

>I'm not singling out Mr Rodriguez here, but we are asked this message >multiple times a week, mostly for Modbus, as well as other PLCs. > >This makes it a prime candidate for a FAQ, but we need to answer the >question. Does anyone know of a good resource on the web for getting >communications components, source code, or what have you for various >brands of PLCs. I'm thinking of a site with links to the documents >containing the protocols, I already have such a site which was advertised several times last year: http://ourworld.cs.com/rahulsebos and I hereby volunteer! >...links to companies selling OPC servers and COM components talking >to PLCs, and links or complete source code to talking to PLCs. This >link could be sent out in a message to those subscribing to the >automation list, and it would make everyone happy! I am also willing to add such links to the section about Modbus (or any other network), however I do not intend to search actively for the information due to limited time, but if the information comes along in this list, I can update the webpage. so 'future generations' don't have to spend much time searching for things. Rob Hulsebos

 

Alex and everyone, If such a site doesn't already exist, Control.com certainly has room and would be happy to provide this resource to the community. A resource section for PLC communications, with code and links to vendors, protocols and other pertinent documents, could fit well into our existing Links section and could start growing immediately. OTOH, perhaps some input from A-List members would help us to design a resource to best meet the group's needs. Post ideas for content and structure, and we can make this happen quickly... Jennifer Powell Editor & Moderator, Control.com and Automation List

 

Hi all I think it's a great idea for Free Source and sharable utilities, the commercial vendors can handle their own advertising. There are collection sites for scientific interests and and others where there is cooperation. This market is not so served because it's fiercly proprietary and competitive. An OPEN site that collects source, information, and free binaries would be useful. There is a modbus.com who would probably be happy to host this, Regards cww

 

At 14:22 12/01/01 -0800, Alex Pavloff wrote: <clip> >This makes it a prime candidate for a FAQ, but we need to answer the >question. Does anyone know of a good resource on the web for getting >communications components, source code, or what have you for various brands >of PLCs. I'm thinking of a site with links to the documents containing the >protocols, links to companies selling OPC servers and COM components talking >to PLCs, and links or complete source code to talking to PLCs. <clip> If anyone has any samples, source code, etc., then they should consider contributing them to the PLC archive. This is exactly what it was established for. ********************** Michael Griffin London, Ont. Canada [email protected] **********************

 

I agree completely!!! Check out www.plcarchive.com and post your code today! &lt;rant> Seriously, we have a resource like this already that is just waiting for some of our illustrious colleagues to participate. Everyone would love to have a resource like this when they are looking for something to take, but few seem willing to post what they have. I regularly contact A-List subscribers off list asking for submissions, and currently seem to be running at about a 10% (or less) success rate. Everyone else is either "too busy" or promises to either post or send to me so I can format and post, but then never seem to get around to it. If you look right now, there are only 5 people who have bothered to contribute *anything* to this resource. If you recall, these was much enthusiasm, and promises all around by everyone that if such a resource existed, the servers would be nearly overloaded by all of the uploading back when this was in the discussion phase. Curt, I am not directing this at you, but taking the opportunity to point out that calling for another site on which to post open code for our industry is really a duplication of effort. Given the lackluster response by everyone I have contacted, I think any other attempts would be doomed. &lt;/rant> I would like to thank Brad, Simone, Michael, Allen, and Anthony for submitting code to the site and helping support this effort. Rather than starting something new, why don't we better use what we have? The plcarchive can be used for more than ladder logic. Brad has posted an excellent tutorial, and if anyone has source code for drivers etc. in C, Pascal, or even punch cards, I am certain we can find a way to incorporate it into the current system. If not, we will rework the site to make it easier to incorporate. (Dan: Feel like I am volunteering you yet?) Just my $.02. I would really like to see the archive utilized for exactly what you are describing, but it will take the effort of those willing to share what they have, not just those who want to share from someone else. It has to be written and shared before it can be reused. --Joe Jansen www.plcarchive.com

 

Actually, the PLC Archive was established, as I remember the discussion that established it, to provide a place to put PLC ladder code snippets that could be used mostly irregardless of the particular brand of PLC one was using. I think it would be an EXCELLENT place to put communication code, but I think that the organization would have to change in order to provide a quick "pick a protocol -- here are ALL the various documentation, source, and some links to other resources for it" so that those looking for info on a protocol don't have to wade through things they don't need, and so that they get what they need. I would be willing to volunteer time to organize (contributing the plc code that I've worked on will be contingent on my employer, of course). Alex Pavloff Software Engineer Eason Technology

 

Joe, this is just a question of scope. It was my understanding that you were collecting examples of PLC code or psuedocode to help people with the bulk of programming solutions where every single crew typically reinvents the wheel. I am an outspoken proponent of eliminating this effort wasted in pointless duplication in all its forms. What you are trying to do with programming is exactly what we are trying to do with platforms and fieldbus. When you develop 50 functionally equivalent solutions instead of using the same one 50 times, you have wasted 98% of the development time. And that's whether you are talking programs, platforms, or fieldbus. What I can't understand is why we can't get people to agree to share and derive the benefits. When there is a non-commercial, politically safe, publicly owned cooperative effort to provide the means there is no downside. Since I don't deal much with PLC (application) code, your effort didn't pop into my mind as the place for it. It should have as we should support the projects as closely aligned as these are. In the spirit of sharing though, open fieldbus access code should reside in your archive, our archive and modbus.org or at least we should arrange for linkage so that people who need it can find it. Our code archive: www.linuxplc.org, contains only GPL code and is free and open for anybody. It does include some modbus code and you are certainly welcome to anything you think can be of use. With the permission of our gracious host, we will link or mirror your archive as well as it is certainly germain. Let's not compete, there's enough of that in this market already. Sorry I forgat you. Regards cww

 

A few comments on the rash of Modbus requests: I see OPC-Foundation has a nifty "by-network" index now: http://www.opcfoundation.org/Search/Network.htm But don't try to use Netscape 4.x as (surprise) it seems only MsIE can handle the javaScript it relies on. I know the control.com moderator is not meant to be Dr. Auto - but at some point if control.com has a good FAQ some of these simple repeat questions could be bounced back with a canned reply of "Check the FAQ/Archive" so that we as valued alist folk don't just waste the air-waves with such bounces. It is interesting to note that the frequency of requests likely relates to the overall population of interest. With an Oil & Gas background, I grew up with the natural notion that Modbus was the safest, most open-optioned multi-vendor interface. Yet visit an AB dealer (or any "big" non-Modbus vendor), mention Modbus and you'll likely be greeted with the same warmth as if you've just told a Frenchman "English is the language of the web". ;-] Plus it's also interesting to note that all the big PLC companies (Siemens, AB, Modicon, GE, Omron) now sell at least a low-end PLC with an internal Modbus option. I remember hearing things like "It will be a cold day in Hell when Company-XXX sells a Modbus PLC" - guess Lucifer may want some ice skates. Regards Lynn August Linse, Senior Product Application Engineer 15353 Barranca Parkway, Lantronix Inc, Irvine CA 92618 [email protected] www.lantronix.com Tel: (949)300-6337 Fax: (949)453-7132

 

As the discussions progressed, we decided that we would break it off into specific categories as the code base grew. The idea was to look for natural boundaries, be they PLC brand, protocol, or whatever best fit the submissions that we were receiving. The problem is that, at the time of this writing, we only have 16 submissions. If we ever do indeed get to the point of wading through things we don't need, then it will be broken into categories. As it stands, there simply hasn't been enough contributed to warrant any sort of categorization. Simply put: There is nothing to organize at this time. As always, any code that you can contribute would be greatly appreciated. The more that we get, the sooner we will start to see what the categories should be, and can start to put different types of submissions into groups. What I don't want to do is to set up a a different section for everything that we can think of, and then have 80% of them just sitting empty. Until we have code to put into a section, there is no reason to create it. In fact, if anything it is detrimental, because someone that comes in looking for info will see the category, click the link, and find it empty. This is pretty frustrating. If they continue looking around the site and see a lot more empty categories, they will simply abandon it as a resource, comparing it to an on-line ghost town. At least with everything in one place, it is easy to see what we do and, mostly, do not have. And there is nothing sitting empty. Please, everyone, try to find just one piece of generic code that you can post. Ladder, protocol, C code, tutorial, whatever. The point is that nothing will be gained if we don't start putting stuff out there! Thanks to all for the support. --Joe Jansen www.plcarchive.com

 

In response to Lynn, Joe, Alex, and others: Since code is so frequently requested for these applications, I agree that the PLC Archive can serve the List well, provided people contribute what's needed. So please contribute! An Automation FAQ would also be very useful, to help minimize repetition. It would reference the PLC Archive for appropriate code wherever necessary. Occasionally I field common, easy questions offline (like the basics of PLC operation, lost passwords, and technical support contacts) based on my memory and archive. It seems logical that Control.com provide this for the benefit of the List, so I'll compile these questions into a usable form, both on the site and as part of the Listserv document everyone gets when they subscribe to the List. I'll post the URL of the Web page to the A-List when it's been created, for your review. If anyone has suggestions for frequently asked questions *you've* noticed and can provide answers (the more comprehensive the better ), or links or anything else, please send them to me at [email protected]. Jennifer Powell List Moderator