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S7 1200 Modbus RTU Connection

Created by: Navid Entezari at: 7/29/2014 7:53 PM (13 Replies)

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7/29/2014 7:53 PM	Rate (2)
Navid Entezari Posts: 40 Rating: (12)	Hello Dear Experts I have a plc1214c DC/DC/DC and CM 1241 RS485. I want to connect 11 hmi Delta to CM 1241 RS485 via Modbus RTU . I tried so much to connecting 11 Hmi and PLC together Via modbus. (using master & slave method),but I not succeed. I could only connect one HMI to plc and Connection Failed when I connect more than one hmi to plc. please help me to solve this problem. thanks for your attention. Best Regards;
Navid Entezari Posts: 40 Rating: (12)
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7/29/2014 10:17 PM	Rate (1)
William_B Posts: 5225 Rating: (1204)	Hi there, Much can be said about how the connection is made. I think it will be helpful for the members to know how you have made a connection between the devices. One think I can think of is the need to have a terminating resistor at the end of the bus. Please give our members as much info as you have to give; including what you have checked already (which includes things like baud rate). The program you use to test with will also be helpful. Do tell our members also how you know the communications are not working.. is it simply not working or is there an error somewhere. Good luck for finding a solution. w LATE NOTE: Much of what you already know about connecting Profibus should apply. It would help the guys a lot if they realise what you have done already, as not going through things you already know and applied.
William_B Posts: 5225 Rating: (1204)	Last edited by: William B. at: 7/29/2014 10:22 PM add late note
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This contribution was helpful to 1 thankful Users Navid Entezari

7/30/2014 6:47 AM	Rate (0)
pratik7332 Bronze Member Joined: 11/26/2009 Last visit: 9/23/2025 Posts: 223 Rating: (1)	hi, Could you give us more information in this manner. IF possible try to apply profibus network in this perticular case.

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7/30/2014 7:47 AM	Rate (1)
Estring Posts: 86 Rating: (3)	Hi all, you cannot connect 11 HMI stations to one PLC via serial port, the RS485 its a single master - multi slaves it means that you can connect one master (HMI or another PLC) to a network of PLC's. in your case you could use modbus TCP/IP on your PLC and then you could connect as much as you would like to HMI. also check your 9pin connector pinout(3-"+" 8-"-"). hope it helps you.
Estring Posts: 86 Rating: (3)
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This contribution was helpful to 1 thankful Users Navid Entezari

7/30/2014 8:03 AM	Rate (0)
William_B Posts: 5225 Rating: (1204)	Estring ..you cannot connect 11 HMI stations to one PLC via serial port, the RS485 its a single master - multi slaves it means that you can connect one master (HMI or another PLC) to a network of PLC's.. Hi there. Modbus RTU over RS485 can handle 1 master and several slaves. Modbus RTU over RS232 is a one-to-one connection. If the Delta HMI can handle this, is another question.. but I am very sure it does not have an issue with handling multiple slaves. It is important however that each device have a unique address. w
William_B Posts: 5225 Rating: (1204)
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7/30/2014 8:35 AM	Rate (1)
Navid Entezari Posts: 40 Rating: (12)	Hello Dear Experts all program is in OB1 and attached in Appendix . thanks for your attention. Best Regards; Attachment program.jpg (784 Downloads)
Navid Entezari Posts: 40 Rating: (12)
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This contribution was helpful to 1 thankful Users William_B

7/30/2014 1:29 PM	Rate (1)
Estring Posts: 86 Rating: (3)	Hi Navid, the program looks fine the issue not with the code though with the hardware connection the RS485 doesnt support multi master topology, you can connect only 1 master in a network. in your case you CANNOT connect 11 HMI devices as master with 1 PLC. if you would like to do so anyway try it with modbus TCP/IP.
Estring Posts: 86 Rating: (3)
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This contribution was helpful to 1 thankful Users Navid Entezari

7/30/2014 2:00 PM	Rate (1)
William_B Posts: 5225 Rating: (1204)	Estring Hi Navid, the program looks fine the issue not with the code though with the hardware connection the RS485 doesnt support multi master topology, you can connect only 1 master in a network. in your case you CANNOT connect 11 HMI devices as master with 1 PLC. if you would like to do so anyway try it with modbus TCP/IP. Sir, I agree that it would not be possible to have the x11 HMI connected as masters. I agree that Modbus TCP would work better for this. Would it however not be possible to have these HMIs connected as slaves? If the Delta HMI can be set as Modbus slave, the PLC could pole each HMI for the information(?). Granted I do not know the Delta make of HMI, but others I have worked with has this option. Thank you for your consideration. w
William_B Posts: 5225 Rating: (1204)
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This contribution was helpful to 1 thankful Users Navid Entezari

7/30/2014 3:34 PM	Rate (0)
William_B Posts: 5225 Rating: (1204)	Dear Navid.. You are being very generous with your star ratings. Mr Greg Estrin and I are hoping for you to find a solution.. not get stars. A star rating means nothing if there is no solution for you. If you have a solution - please be so kind as sharing the facts with us. - Is it possible to connect the HMI as a slave? - How does the physical connection look like? Thank you. w
William_B Posts: 5225 Rating: (1204)
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7/30/2014 8:05 PM	Rate (0)
Navid Entezari Posts: 40 Rating: (12)	Hello Dear Expert All answer is true. But,I did not check yet. After connection check, I will report the result to you. Thanks for your consideration. Best regards,
Navid Entezari Posts: 40 Rating: (12)
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