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We're evaluating cpppo to talk to various Rockwell Automation PLCs. We have address ranges in form "N25:00" (N = integer, file number 25, file offset 0), but EtherNet/IP seems to want @<class>/<instance>/<attribute>.

How do you translate from one to the other?

If tags were defined in these PLCs, is there a way to get a list of them, or information about them? We have no ability to change the PLCs, and usually can't see the ladder logic/configuration in them.

cpppo's list_identity, list_interfaces, and list_services all work, but don't return anything that seems to translate:

List Services  0 from ('10.91.xxx.yyy', 44818): {
    "count": 1,
    "item[0].communications_service.capability": 32,
    "item[0].communications_service.service_name": "Communications",
    "item[0].communications_service.version": 1,
    "item[0].length": 20,
    "item[0].type_id": 256
}

List Interfaces  0 from ('10.91.xxx.yyy', 44818): {
    "count": 0
}
JimB
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  • @pjkundert any thoughts? – JimB Feb 13 '17 at 09:39
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    Hi, Jim; The addressing you gave is actually Modbus addressing. Some *Logix PLCs (maybe all of them?) support Modbus/TCP I/O, in addition to EtherNet/IP CIP. What I understand, is that the data is available from both protocols -- under Modbus/TCP, it'll be addressed in the N25:00 method. In EtherNet/IP CIP, it'll be located at some // address. However, I've never configured this in a *Logix PLC, so I don't know how to discover what (if anything) is the CIP address that corresponds to the same data as has been made available via the N25:... Modbus addressing. – pjkundert Feb 15 '17 at 00:05
  • Thanks for the thoughts. We've done quite a bit of Modbus, and this doesn't match anything I've seen. Modbus has a single address, typically in the 40001 range for integers. This addressing fits with Rockwell's (Allen-Bradley's) DF1 protocol (which these PLCs are), but that's RS-232, not Ethernet. I hoped EtherNet/IP was an extension. – JimB Feb 16 '17 at 03:40
  • You are right, I'm sorry -- I was mixing up Allen Bradley Data Highway addressing with Modbus! Sorry for that. Of course, you're right -- Modbus uses numeric ranges to distinguish data types, not N:..., etc! Yes, there are way to tunnel DF1 via EtherNet/IP CIP, but I haven't had any experience with that... – pjkundert Feb 17 '17 at 13:59
  • Looks like it's called "AB/Ethernet (CSP)", and there isn't a whole lot out there outside of dedicated comm modules. – JimB Feb 17 '17 at 15:09

2 Answers2

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You left out an important detail info. What kind of Rockwell PLC? The N25:00 address could be the older PLC type like SLC5, PLC5 series. On the other hand Ethernet/IP is used in the newer tag-based PLC like Compactlogix, ControlLogix PLC.

btw, there's PyLogix that will talk to the newer type PLC.

Phi Bach
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It looks like you will need a gateway of some type. I'm using a commercial product called cogent data hub to get my rockwell data into a SQL database. Not sure that helps you much.

At the very least you'll want some sort of DDE/OPC server. You can use RSLinx Classic for that if you bought it.

Bill J.
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