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Old April 16th, 2018, 12:56 PM   #1
richleva
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Exclamation MODBUS TCP, Need Help!1

Hello,
I need some help/advice. I have a Micrologix 1400 series B on surface at a mine site. Underground I need to read hart data from a flow meter. We installed the Schneider STB with hart Modules. I can see that the STB module is properly retrieving all the data from the flow meter. But my problem is getting the PLC to retrieve the data from the STB module Via Modbus TCP.

I know that the ML 1400 Series B is compatible with Modbus TCP, I enabled it in the programming and setup my message instructions. But after I toggle a bit to enable the MSG instruction I get error "Local Communication is shut down?"

I made sure to enable the Modbus TCP Features.

As for the Schneider STB module, I can connect to it remotely from surface no problem and make changes to it, as needed.

I attached two Screen shoots of the RSlogix MSG configs for the totalizer and the STB registers.

Any advice is very appreciated.

Thanks everyone
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Old April 16th, 2018, 01:44 PM   #2
OkiePC
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Quote:
Originally Posted by richleva View Post
But after I toggle a bit to enable the MSG instruction I get error "Local Communication is shut down?"
This is (in my experience) a sure sign that you need to power cycle the PLC to get the changes to the Ethernet port to properly take effect.

Also, the node number (Unit Identifier) of 255 looks suspect. I'm not familiar with your other device, so it might be okay...some devices ignore the node number with Modbus TCP altogether since you are calling them out by IP address.
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Old April 16th, 2018, 01:50 PM   #3
Ken Roach
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RA Knowledgebase confirms; when you enable Modbus/TCP on a MicroLogix 1400, you must power cycle at least once to reset the communications stack.

https://rockwellautomation.custhelp....il/a_id/117801
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Old April 16th, 2018, 02:03 PM   #4
richleva
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Ok Thanks Guys, I will try this tomorrow. But, when downloading to the controller. does it not cycle power on its own? Or maybe not...
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Old April 16th, 2018, 02:17 PM   #5
OkiePC
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Quote:
Originally Posted by richleva View Post
Ok Thanks Guys, I will try this tomorrow. But, when downloading to the controller. does it not cycle power on its own? Or maybe not...
Not. It's only when making changes to the channel settings that a power cycle is required. Just changing the IP address may allow comms to keep working at least for a short while, but any changes to the port call for a power cycle. Enabling Modbus TCP and then going to run mode without power cycling has given me that same error.
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Old April 16th, 2018, 09:58 PM   #6
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Quote:
Originally Posted by OkiePC View Post
This is (in my experience) a sure sign that you need to power cycle the PLC to get the changes to the Ethernet port to properly take effect.

Also, the node number (Unit Identifier) of 255 looks suspect. I'm not familiar with your other device, so it might be okay...some devices ignore the node number with Modbus TCP altogether since you are calling them out by IP address.
its been my experience that more times than not the unit id/slave id/node id whatever you want to call it, is significant even in modbus/tcp. you may want to ensure you are using the proper slave id number in your modbus poll.
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Old April 17th, 2018, 11:14 AM   #7
richleva
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Talking

Quote:
Originally Posted by OkiePC View Post
Not. It's only when making changes to the channel settings that a power cycle is required. Just changing the IP address may allow comms to keep working at least for a short while, but any changes to the port call for a power cycle. Enabling Modbus TCP and then going to run mode without power cycling has given me that same error.
Everything Worked Perfect after the power cycle !!!
Thank you very much
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