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friedmators

Control Logix (address doesn't point to something usable)

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Hi, Have a DCS system trying to communicate with some recently retrofitted Control Logix processors. They used to be serial and were converted to ethernet. When making data requests I get a 'read reply error: address doesn't point to something usable'. Removed all points except one from my requests to narrow it down. I am requesting N10:0 which looks to be correctly mapped inside RSLogix. We have other similar processors working on site so I know this is not a driver issue per say. The only thing I see odd is when I connect in Logix, the new ethernet card is not listed. Using Linx I was able to configure the card with an IP and gateway and I am connecting up through that card so it seems to be working. Any thoughts would be appreciated.

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I think that when you say "listed", you mean "in the I/O tree" of the RSLogix 5000.Controller Organizer window. Ethernet modules don't need to be in the I/O tree if they aren't used for I/O connections. It sounds like you added a module just for HMI access. What model and revision of DCS are you using ? Is it really ControlLogix -aware, or are they using PLC-5 data table emulation ? What model of ControlLogix ? Is the firmware newer than your existing controllers ?

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Thanks for the reply. We are talking to Ovation here. Not sure exactly what you are asking since I am an Ovation guy but the controller is a 1756-L61 Revision 16.7 We have 1756-L63 Rev 16.56 working here amongst others. Is there a way to debug from the Rockwell side to see why it doesnt like my requests?

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This sort of thing used to be my main business, and I went after it with FrontLine Test Equipment's NetDecoder software. Most folks start with Wireshark and a mirroring switch. Are the controllers all in Slot 0 ? That's the traditional Slot number for ControlLogix but they can be elsewhere. Many third-party drivers hard-code the Slot number, especially if they are using PLC-5 emulation. Are you sure you're using the right driver and defining the right controller type in Ovation ? I'm asking because the older PLC-5 controllers (before 1998 or so) support only a proprietary A-B protocol, while modern PLC-5 controllers support the "EtherNet/IP" protocol. Maybe Ovation implemented both protocols. Over serial, the protocols are identical. Over Ethernet, they are different. One very simple way to determine the protocol Ovation is using is to look at the TCP port that the Ovation is trying to access. If it's TCP Port 2222, it's the old proprietary protocol. TCP Port 44818 is the modern EtherNet/IP protocol. Those version numbers suggest that these are Redundant controllers. Are you connecting to them directly over Ethernet, or are you routing into the system via ControlNet ?

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Quick update: Using the Wonderware AB CIP Driver, I was able to see data from the PLC using the tag name itself. However, requesting N10:0 resulted in a similar error the Ovation DCS was reporting. Seems to be a mapping issue. Ovation allows Slot selection. Everywhere else on site its Slot 0, here its slot 7. 44818 for slot 0, 1792 for Slot 7. Non-redundant. I am thinking we are going down the right path. I have another PLC using the same exact ethernet card and revision number and N registers and its working in Ovation. I was going to confirm wonderware can speak to it using N registers which would pretty much isolate the issue down to the mapping. I did a cursory glance at the configurations of the two PLC's and couldn't find any differences other than the location of the ethernet cards/CPU in the I/O tree though.

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