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Modbus TCP communication - using one S7-1500 as a slave, and a central PC as master

Created by: NPlayer at: 12/4/2014 8:50 AM (13 Replies)

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12/4/2014 8:50 AM	Rate (0)
NPlayer Posts: 20 Rating: (0)	Hi! I'm going to implement Modbus TCP communication in my current project. I'm using one S7-1500 as a slave, and a central PC as master. This PC has a custom software, probably visual basic, and it communicates with all the other Siemens PLC via Modbus TCP. Let's see if I understood this: I have to make, at least, two MB_CLIENT instances, one to write values, and other to read values, right? The PC software will read values from the PLC and, if the user needs it, write or changes some of the values in the PLC. I can do this with these blocks right? Your help will be very much appreciated, thank you! ----------- new subject after splitting from Sample Program: Modbus TCP with S7-1500
NPlayer Posts: 20 Rating: (0)	Last edited by: CS Moderator at: 12/4/2014 11:41 AM splitting
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12/4/2014 7:49 PM	Rate (0)
Rafael Fernandes Experienced Member Joined: 2/19/2014 Last visit: 10/15/2024 Posts: 8 Rating: (0)	Hello, You can use the same interface and the same port in the PLC (default port is 502) , however your application should open only one connection and perform one request at a time, I don´t see any problem to use the same socket for that. It worked fine during my tests here. Good luck. Rafael
	Industrial Automation / IT Systems Analyst
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This contribution was helpful to 1 thankful Users NPlayer

12/8/2014 11:27 AM	Rate (0)
Gkp Raina Posts: 40 Rating: (0)	Hello, Yes ,you can use two blocks in MB_CLIENT for Read and Write .You have to change the connection ID for the second one.i.e both blocks should have different connection ID .here i am attaching a sample program which i did for testing in (TIA v11 sp2).In this program i used 1212c DC/DC/DC cpu. Regards Prasanna Gk If u found this post helpful ,please rate this post. Attachment Modbus tcp PLC asCLIENT.zip (1963 Downloads)
Gkp Raina Posts: 40 Rating: (0)	Last edited by: Gkp Raina at: 12/9/2014 11:55 AM
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This contribution was helpful to 1 thankful Users NPlayer

12/9/2014 11:43 AM	Rate (0)
NPlayer Posts: 20 Rating: (0)	Oh thank you for your answers and examples! I am looking at your example Gkp Raina. I wonder if I use the same DB area for writing and for reading, could that work? Also, I use a Master Simulator to test the slave PLC, which would be the Device Id if I want to communicate with these type of software? It's the same as the MB_CLIENT ID? Thanks!
NPlayer Posts: 20 Rating: (0)
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12/9/2014 12:03 PM	Rate (0)
Gkp Raina Posts: 40 Rating: (0)	Hello , If you want to keep your plc as slave (server) ,you have to use MB_SERVER block.In server ,you Will have only one connection ID ,you can connect as many as 8 clients (varies on CPU and Firmware versions) to that server.I did a sample code and am attaching that that here. Regards prasanna GK If u find this post helpful,please rate this post Attachment Modbus tcp PLC as SERVER.zip (1522 Downloads)
Gkp Raina Posts: 40 Rating: (0)	Last edited by: Gkp Raina at: 12/9/2014 12:20 PM
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This contribution was helpful to 2 thankful Users NPlayer jkota

12/9/2014 12:23 PM	Rate (0)
NPlayer Posts: 20 Rating: (0)	Yes, my customer have a central PC which is configured as a master, and the rest of the PLC's have to be configured as slaves. So I have to use the MB_SERVER? I was totally confused about this. I made the analogy Master-Server, Slave-Client. So I was confused, let's see that example. Thank you!!
NPlayer Posts: 20 Rating: (0)
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12/9/2014 12:30 PM	Rate (1)
Kaulquappe Posts: 3093 Rating: (323)	Hello NPlayer, client and master are active and slave and server are passive. The mnemonic trick is the two "S" are identical and they are pa"SS"ive. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (323)
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This contribution was helpful to 2 thankful Users Sakura NPlayer

12/9/2014 12:37 PM	Rate (0)
NPlayer Posts: 20 Rating: (0)	Kaulquappe Hello NPlayer, client and master are active and slave and server are passive. The mnemonic trick is the two "S" are identical and they are pa"SS"ive. Regards, Kaulquappe Great trick! So much resources wasted just for this misunderstanding! I will try again with all this information, and share the results! Great forum, thank you!
NPlayer Posts: 20 Rating: (0)
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12/9/2014 6:59 PM	Rate (0)
NPlayer Posts: 20 Rating: (0)	Hi again! I've been able to connect to the PLC via a Modbus Simulator software. I can read input and output states with Read Coils and Read Discrete Inputs. When I choose to read Input Registers, I get some data in the first 5 registers. The first one is the value of all the inputs. The rest I don't know where do they refer. When I choose to read Holding Registers (function 03), the software gives me an Illegal address, so I can't read the struct I use as MB_HOLD_REG. I read in the MB_SERVER documentation something about the MB_HOLD_REG input, but I don't really know what I have to put in order to read the values I want with the 4xxxx addresses. Thanks for the help!!
NPlayer Posts: 20 Rating: (0)
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12/10/2014 4:59 PM	Rate (0)
NPlayer Posts: 20 Rating: (0)	SOLVED! I can read and write variables with the Function 03. The issue is the MB_HOLD_REG. I have a struct inside a DB --> MyDB.MyVar. And I used this variable for the MB_HOLD_REG Input of the MB_SERVER. This was giving me error 8383, and error related to the data being out of range. I solved this by unticking the Optimized access block in the properties of the DB. And then, insted of using MyDB.MyVar, I used this P#DB103.DBX0.0 WORD X, being X the length of the variables (X = 10, max variable is 40010). So, for now, everything seems to work perfectly. Also there is a KTP600 atached to the other ethernet port of my s7-1500 comunicating via profinet and it's also working! The only thing I would like to know is how to use two instances of MB_SERVER or if it's possible.
NPlayer Posts: 20 Rating: (0)
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This contribution was helpful to 3 thankful Users Kahl Min_Moderator PetriLaiho66

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