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Old July 19th, 2015, 11:50 PM   #1

scrambled is offline
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Omron CJ1W-ETN21 Automatic Address Generation Error

I have an Omron CJ1M PLC that does Modbus TCP comms via an CJ1W-ETN21 Ethernet module.

At the moment, I have set the ETN21 to automatically generate its node address from the last octet of the IP address. In my case, my test IP address has 156 as its last octet. So I set the two node address dials to 9C (hex equivalent) on my ETN21 module. Should be fine right?

However, when I do so, I get an ERH flashing LED on the ETN21, indicating an "address disagreement". Modbus TCP comms works fine but I'd like to find out why the ETN21 is giving me this error.

I checked the CIO error word and the "address disagreement" bit is the only one that is turned on. What is even more peculiar is that the error goes away if I manually add an IP address table entry routing node address 156 to my IP address which ends in 156. I've attached a screenshot of this configuration.

If I remove the IP address table entry and set the node address conversion back to automatic (dynamic), the error comes back again. This is without touching anything else in CX programmer and the ETN21. I've spent the last hour looking through all the Omron manuals and have not been able to figure out why this is occurring.

Can anyone here point me in the right direction?
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Old July 20th, 2015, 05:43 PM   #2
Sergei Troizky

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With your subnet mask, the most significant bit of the last octet belongs to the network ID, not to the node number.
Try 1C instead of 9C.
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Old July 21st, 2015, 09:26 PM   #3

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Thanks Sergei, that was indeed the problem. Giving it 1C as the node number made the error LED go away. Funny how obvious the problem seems in hindsight.
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