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PaulB

Ethernet IP node swap on the fly

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I have a question about functionality of the Ethernet IP network. Is it possible to plug and unplug network nodes on the fly? For example if we have Control Logix processor as supervisory PLC. In that PLC we have program loaded, which has, maybe, about 100 - 150 nodes of Ethernet IP IO adapters in its IO configuration tree. These nodes all inhibited. As soon as you plug one of the nodes to the network it becomes uninhibited. Total number of nodes physically connected to the network always will be much less, maybe, 20 -30 nodes. I know that using SSV instruction it is possible to inhibit or enable module communications. I am not sure how to let PLC processor know that this particular node is connected or disconnected. When you run RS Linx on the computer and browse the network, nodes that are not seeing (unplugged) have red cross over them. When node is plugged RS Linx starts seeing this nod and red cross disappears. Is there any way to pass information about "red cross" appearance from RS Linx to the Control Logix processor? Thank you PaulB.

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I have not done a system exactly like this, but do have one coming in the future with 64 potential nodes connected to 4 controllers, which can "swap" banks of nodes by physically connecting machines together. My plan is to put together a logic routine that performs a "List Identity" service request message to each IP address that can potentially have an I/O node associated with it. When you get a successful List Identity response, the logic can check to be sure the device is really the expected I/O device, then it will un-inhibit the correct I/O connection. There are going to be a great many SSV/GSV and MSG instructions involved in such an endeavor, but if you're careful and plan well, they don't have to take up too much time and memory. The "List Identity" function is called a "Device Who" in the MSG configuration. It returns the Identity Object of a device, which is exacly how RSLinx determines what device type and revision is on the network. Ethernet timeout values can be relatively high, so plan on manually timing out your List Identity requests by setting the .TO bit of the message control tag when the .EN has been true too long without the .DN becoming true.

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Ken, thank you for the quick response. Where can I read about "List Identify" and "Device Who" in Rockwell documentation. I've made quick search in 1756-RM003J-EN-P, Logix5000 Controllers General Instructions Reference Manual without results. PaulB

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There is a description of the "Device Who" function in CIP Generic Messaging in RA Knowledgebase Answer ID # 23386. http://rockwellautomation.custhelp.com/cgi...p?p_faqid=23386 You could use this to verify down to the device serial number if you wanted.

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Thank you, Ken. I'll read this.When you are saying Ethernet time out values may be too high. What numbers do you have in mind few seconds, few minutes? Paul.

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