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Modbus TCP Two UNIT one PORT

Created by: Joel Rock at: 5/11/2015 10:48 PM (8 Replies)

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5/11/2015 10:48 PM	Rate (0)
Joel Rock Regular Member Joined: 12/29/2014 Last visit: 11/12/2024 Posts: 16 Rating: (0)	Hi all, I am implementing a project in which I have been asked to program a PLC as server. In addition, they ask that internally the PLC responds to requests from the TCP client. But the client makes requests to UNIT 20 and 21 by the same port. As I understand the MODBUSCP block as the application server only responds to one. Deputy my chart, I'm waiting for your help. Attachment MODBUS TCP.png (293 Downloads)

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5/12/2015 12:31 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (323)	Hello Joel, the FB MODBUSCP acting as server echoes the received UNIT. So it is possible that the client uses different UNITs. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (323)
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5/12/2015 4:17 PM	Rate (0)
Joel Rock Regular Member Joined: 12/29/2014 Last visit: 11/12/2024 Posts: 16 Rating: (0)	Thanks for your answer Kaulquappe. If the client units. Is there any way to read the unit that sends the client and change the DB assigned to "ID1_db_1" the PARAM_MODBUSCP. Example: If the client (IP: 10.25.24.8) requires holding register read function unit 20 and the read coil unit 21. How do I can answer as it is shown in the attachment? Also, I can only program the server PLC program because I do not have permission to make any changes to the client (SCADA). Attachment wireshark_crp10.jpg (259 Downloads)
	Last edited by: JoelHuaman at: 5/12/2015 4:24:54 PM Last edited by: JoelHuaman at: 5/12/2015 4:26:57 PM Last edited by: JoelHuaman at: 5/12/2015 4:34:52 PM
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5/12/2015 5:22 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (323)	Hello Joel, it is not possible to modify the data source/destination at S7 side during runtime depending on the received unit. Does the client read identical registers/coils? If the addresses are different, there will be no problem. When identical register addresses are accessed it will become complicated. Would it be possible that the client establishes two TCP connections, one for unit 20 and one for unit 21? If yes, there could be a solution by using the integrated ethernet interface of a PN CPU - but some things must be evaluated in advance. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (323)
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5/12/2015 6:01 PM	Rate (0)
Joel Rock Regular Member Joined: 12/29/2014 Last visit: 11/12/2024 Posts: 16 Rating: (0)	Hello Kaulquappe, If the client reads the same directions of both units. The server I'm programming PLC has the following DB's: DB60 (Holding_reg) unit 20 DB61 (Holding_reg) unit 21 DB62 (coil) unit 20 DB63 (coil) unit 21 Unfortunately I can not change anything on the client (SCADA) because we have not authorization to modify the database, or the port. It would be helpful if the MODBUSCP unit can also be configured in server mode. We can not change the PLC modules because it has all the hardware. It is using the CP-341 Lean. How hard it is to change the port Survalent SCADA? A viable solution would do the following: SERVER (Can I have 2 ports as a server to a client?) PORT 502 (unit 20) <----------> PORT 2000 (SCADA client Survalent) PORT 503 (unit 21) <----------> PORT 2000 (SCADA client Survalent) Regards, Joel
	Last edited by: JoelHuaman at: 5/12/2015 6:05:27 PM
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5/13/2015 12:06 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (323)	Hello Joel, this would be the best solution: use two different local port numbers at S7 side. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (323)
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5/13/2015 5:04 PM	Rate (0)
Joel Rock Regular Member Joined: 12/29/2014 Last visit: 11/12/2024 Posts: 16 Rating: (0)	Hello Kaulquappe, First, thank you for your answers, they are very useful. I have a program that performs communication using two slaves 20 and 21 via Modbus TCP, but does not use the MODBUSCP block. Could review and give me an explanation broadly. As communication has achieved the MODBUSCP block? If using the AG_SEND and AG_RECV can achieve Modbus TCP? If this is possible then how could form the Modbus TCP frames. I have understood that the Modbus TCP protocol is comprised of: Transaction identifier, Protocol Identifier, Lenght Field, Address(Modbus), Funcion code (Modbus), Data (Modbus) and Checksum. You will have some idea of how to form the plot as it does in the program that you attached. Regards, Joel Attachment TCP_BACKUP.zip (278 Downloads)
	Last edited by: Joel Rock at: 5/13/2015 5:05:56 PM
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5/14/2015 7:07 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (323)	Hello Joel, I do not recommend to realise the ModbusTCP protocol on your own. It is a lot of work, even if you focus on the functions you need for your application. You can do it with AG_SEND and AG_RECV, of course, but it will take you weeks. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (323)
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This contribution was helpful to 1 thankful Users Joel Rock

5/14/2015 9:18 PM	Rate (0)
Joel Rock Regular Member Joined: 12/29/2014 Last visit: 11/12/2024 Posts: 16 Rating: (0)	Hello Kaulquappe, It would be interesting to make a block of free Modbus TCP communications :) Well, I'll see that other solutions can perform. Thanks for your help. Regards, Joel

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