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S7 1200 1214C CPU and Modbus TCP?/IP communication

Created by: Aditya Gupta at: 12/7/2013 6:48 AM (7 Replies)

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12/7/2013 6:48 AM	Rate (0)
Aditya Gupta Posts: 4 Rating: (0)	Hello Everyone, I am New to PLC Automation Field. I am working on a Project where siemens S7 1200 is used, it is connected to a Ethernet Switch. The data is coming from a Modbus Device via Ethernet Cable, which is connected to the same switch. Also i am running a OPC Server on a Laptop which is connected via LAN cable to the same Switch. Now the Problem is that i want to grab the Data from PLC Registers to OPC Server running in the Laptop, but i am unable to do so. What might be the problem? Will i require any modbus to Ethernet Converter to convert data from Modbus device to a form where PLC can interpret it? can anyone please help me?
Aditya Gupta Posts: 4 Rating: (0)
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12/8/2013 11:52 AM	Rate (0)
jklm Platinum Member Joined: 12/22/2006 Last visit: 1/25/2022 Posts: 1742 Rating: (309)	Hello, There are 3 protocols (communication languages) involved in your setup. 1) The PLC speaks Modbus with the third party device. - the Modbus regsiters are usually stored in a datablock in the PLC. 2) The PLC could speak S7 protocol with the PC loaded with the OPC server. - allows you to read/write to a databloc, even from/to the datablock containing the Modbus registers. 3) The OPC server speaks OPC with an OPC client(s). - the OPC clients can be an application running on the same PC or an extra PC, like OPC scout, WinCC, ... How to set up the S7 communication between the PLC and the PC using an OPC server is described here: http://support.automation.siemens.com/WW/view/en/39960679 Hope this clarifies the situation.
	Last edited by: jklm at: 12/8/2013 11:57 AM Best regards jklm Suggestion was helpful? Feel free to rate it.
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12/9/2013 5:51 AM	Rate (0)
Aditya Gupta Posts: 4 Rating: (0)	thanks alot jklm, it was really helpful. But i would like to know one more thing, does the communication between the modbus device and PLC requires any additional Hardware like Modbus Add on Card or the PLC itself takes care of the protocol conversion?
Aditya Gupta Posts: 4 Rating: (0)
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12/9/2013 8:14 AM	Rate (0)
SMHZ Bronze Member Joined: 10/19/2012 Last visit: 4/17/2022 Posts: 315 Rating: (9)	I dont think so there will be requirement of other additional card/module. Can u mention which S7-1200 CPU u r using?

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12/9/2013 11:21 AM	Rate (0)
Aditya Gupta Posts: 4 Rating: (0)	Hi, The CPU i am using in this project is 1214C..
Aditya Gupta Posts: 4 Rating: (0)
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12/11/2013 2:16 PM	Rate (0)
Fafner Silver Member Joined: 3/20/2013 Last visit: 3/21/2025 Posts: 676 Rating: (44)	hey! to speak to your modbus tcp device with the plc (cpu 1214c) you can use the modbus-instructions of this cpu. they are called MB_CLIENT and MB_SERVER. Some hints to this topic can you find in the forum like here and here. here is an FAQ for the VARIANT datatype. You can find more topics to the MB_CLIENT and MB_SERVER in the forum and in the online help.
	Best Regards, Fafner
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12/13/2013 9:33 AM	Rate (0)
Aditya Gupta Posts: 4 Rating: (0)	hi, thanks for your reply, I understood what you told, but my confusion is that the media is Ethernet cable and i have heard Modbus always works with RS-485, so will there be any requirement of RS-485 to Ethernet Converter?
Aditya Gupta Posts: 4 Rating: (0)
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12/13/2013 9:55 AM	Rate (0)
Fafner Silver Member Joined: 3/20/2013 Last visit: 3/21/2025 Posts: 676 Rating: (44)	There is Modbus RTU (RS485) and Modbus TCP (Ethernet) . Perhaps have a short look about that in wikipedia, or sth. else.
	Best Regards, Fafner
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