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Old April 7th, 2009, 01:48 PM   #1
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Red face Automation Direct Modbus TCP

Hello everyone,
I have been pulling my hair out on this one. I have been unsucessful in communicating Modbus TCP to a Eurotherm Data recorder using an Automation Direct D0-06 PLC. I have all but exhausted any tech support from either manufacture. The PLC is the master and the Eurotherm Data recorder would be the slave. I'm using the H0-Ecom100 ethernet card running through an ethernet cable to the Eurotherm. I have upgraded firmware in the processor to the latest automation direct has out. I have used the examples in the manual chapter 5 (in testing). I have converted the modbus address using Automation direct's conversion sheet (decimal to octal). Can anyone offer me any advice on this matter? Any helpful advice would be very appreciated.
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Old April 7th, 2009, 03:49 PM   #2
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I am by no means an expert on this stuff, but I'll bet that you need to put an Ethernet switch...I was just on the phone w/ AD tech and they said make sure that you go into NET EDIT and change the peer to peer table for the modbus tcp, which I think you said you had done. Check it again. You will need a cross-over cable unless you add a switch...

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Old April 7th, 2009, 04:48 PM   #3
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I agree with David. Running point to point, you either need a crossover cable or a switch with straight cables.

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Old April 7th, 2009, 04:56 PM   #4
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Plug a pc in one end and try to ping the other that will show wether you need a switch or cross-over cable. Have a look onthe net for a shraeware called SimplyModbus it has a demo mode (or buy if think it's good) I've used it to test comms reasonably easy to set up and lets you change stuff on the fly (big-endian etc)
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Old April 7th, 2009, 09:27 PM   #5

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Download the wireshark application. Assign a fixed IP to your master, slave, and your pc (of course, make them all similar, ie Get yourself an old ethernet hub, and connect all 3 devices to the hub. Run the wireshark application from your pc. Be careful, if you have a real tight IT department, you may not see the communications between master and slave - in which case use a home laptop or something. You should be able to see the modbus tcp communications as well as the specific modbus queries. If you have another slave that is responding, then connect that as well. That way you can compare. Another idea is to download a Modbus tcp simulator/tool. There are tons of them for free...If you can see the communications between master and slave in this setup, then it is likely that ports (specifically 502) are being blocked in the field setup.

Good luck.

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Old April 8th, 2009, 09:28 AM   #6
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I concur with Mike on using Wireshark to diagnose this situation.
Once you have captured the data, you now have more information to go to both/either of the manufacturers to show them what is going on.
You can also post the capture file back into this thread for others to help.
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Old April 17th, 2009, 11:36 AM   #7
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RE: Automation Direct Modbus TCP

Thank you for all of your help,
I will look into this.

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