Message exchange with ControlLogix

[Guest RobinBaxter]

I am working with a client who is planning to use ControlLogix PLCs to control a material handling facility. They already have AB PLCs communicating with DH2 on exisiting plant, and are planning a new facility. They use RSLinx to program the current PLCs. We supply a Manufacturing Execution System for the current facility and interface to the material handling using DH2. For the new facility, we will be using the same MES, but need to communicate with the ControlLogix. For other equipment in the facility, we are using TCP/IP with Winsock, and would like to use the same method for the comms to the AB PLCs. We are not doing the PLC programming - all that we want to do is send a message to the AB PLC to request an action to be performed on the PLC, and to accept status information back from the PLC. It appears that we can do this by making use of the SDK from AB, but is there a simpler way? Is it possible to obtain a specification of the interface (in simple form) that allows us to make a connection and send and receive action messages. I have looked at the Ethernet/IP spec, but this covers far more than we need, and it is difficult to find the bits that are necessary. For example, if I am a server waiting for a connection from the AB controller, I get a message requesting connection but do not know what to reply to accept the connection. Is there a simple way to locate this? Our ideal would be to use Winsock on a PC to make the connection and test out the set of messages that we wish to exchange with the AB PLC. The target installation is VAX VMS, so all that we would then have to do is develop the same message exchange in C on the VAX - we already have the Winsock equivalent which we are using for comms to the other plant in the facility. Doing it this way, we can have emulators on PCs for the AB plant to enable us to test the MES actions, and a PC driver to test the message exchange to the AB PLCs. Hope someone can provide some advice here.

[Chris Elston 78]

How many times is the data going to be requested? Once a minute? Once every 10 mSeconds? How much data is being transferred? one bit? two bits? 200 words? It you don't have alot of data, the "easiest" way is a DDE connection. Some guys in here will tell you that is old stuff, but to me it's easy, fast and it works. If you need to move alot of data, an OPC connection would be a better choice. You can do your owe OPC connection in VB etc...or you can buy pre-made ones from various companies. OR you can buy pre-made ActiveX modules like this one: http://www.mrplc.com/dl/index.php?action=v...ntry&entryid=39 But there are alot of OPC server/client apps out there that can be bought for around $300.00. Do a search "OPC Allen Bradley" DDE is built into RS Linx so is OPC for that matter, but DDE is easy to create a "topic" and request that topic in an MS application such as Excel. Here are a few DDE examples: http://www.mrplc.com/dl/index.php?action=v...ntry&entryid=34 http://www.mrplc.com/dl/index.php?action=v...ntry&entryid=74 Visual Basic to DDE: http://www.mrplc.com/dl/index.php?action=v...ntry&entryid=58 Hope that helps.

[Guest Guest]

The ActiveX control is interesting as is the DDE - thanks for those. The ActiveX one uses DH+, and we would prefer to use the Ethernet module as this makes the cabling easier. As for message size and frequency, we are looking at the transfer of less than 100 bytes of information every 15 to 30 seconds, so not a particularly high load.

[Chris Elston 78]

Sounds like DDE would work for you application then. DDE will work over any link, as long as a topic is created in RS Linx. You'll need RS Linx Professional version, which is you already have RS View running or some type of big network, they should already have RS Linx Pro. DDE can talk on just about any protocol that I've used. I setup a TOPIC in RS Linx to a PLC, in ethernet, DF1, DH-485 and DH+. I've used them all. Works like a champ. The key is RS Linx however. If you any more questions, please post them here, there a tons of people in here in that can help.

[Ken Roach 194]

I would strongly recommend that you team up with Pyramid Solutions (www.pyrasol.com) and use their EtherNet/IP protocol stack. Pyramid is very well versed in ControlLogix connectivity; in fact, they build several products that go to market with an A-B logo on them. The best part about their Adapter software product is that they've ported it to several operating systems; Win32, WinCE, UNIX, and several embedded systems. That means they've already done the hard work to let you test on Windows and run on VMS. I've had two customers do this "the hard way". From one of them I have a file of e-mails demanding, pleading, and threatening for SLC-5/05 protocol examples. Another one borrowed my ControlLogix sales demo for two weeks... and kept it for nine weeks. The third implemented Pyramid's adapter stack in Solaris and is getting ready to ship their first sixteen remote stations. If you're dead-set on doing this yourself, go get the "ControlLogix Data Access" reference document. This should help you narrow down the services of EtherNet/IP to the subset that deals in ControlLogix tag access. http://www.ab.com/manuals/cl/1756-RM005A-EN-E.pdf

[Guest Guest_Peter Nachtwey]

Ron Gage has two AB Ethernet libraries. One for the older CSP protocols and the other for the newer Ethernet/IP protocol. Just do a google search for Ron Gage. I know people that have implement the CSP protocol with little difficulty. Don't do this from scratch unless you have a lot of time/money to invest. 9 weeks doesn't sound long enough for Ethernet/IP. CSP is much easier.