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Modbus TCP/IP - Sending and Receiving Data

Created by: BenB at: 6/21/2013 4:19 PM (4 Replies)

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6/21/2013 4:19 PM	Rate (0)
BenB Advanced Member Joined: 3/5/2013 Last visit: 7/25/2024 Posts: 21 Rating: (0)	Hello, I am currently using an S7 1214c CPU and I have a Banner Wireless gateway that is functioning as a Modbus Client. I want to set the CPU to function as the Modbus Server so that I can send and receive data to the holding registers of the device. I have used Modbus RTU before, but never TCP. For RTU there are send and receive blocks that allow data to be transferred. The only block I see in Step 7 V12 is the MB_SERVER block. I also see a TSEND_C and a TRCV_C block, but I'm not sure if they are to be used for Modbus TCP. So, my questions are: 1. How do I set up the Step 7 V12 program establish a connection with my client device? How can I verify this connection? 2. Once a connection is made how can I send and receive data to the client device? Do I use data blocks to hold the read data and the data to be written? Any help with this would be greatly appreciated! Thank you, BenB

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6/21/2013 4:44 PM	Rate (1)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 12/23/2024 Posts: 15531 Rating: (2461)	BenB Hello, I am currently using an S7 1214c CPU and I have a Banner Wireless gateway that is functioning as a Modbus Client. I want to set the CPU to function as the Modbus Server so that I can send and receive data to the holding registers of the device. I have used Modbus RTU before, but never TCP. For RTU there are send and receive blocks that allow data to be transferred. The only block I see in Step 7 V12 is the MB_SERVER block. I also see a TSEND_C and a TRCV_C block, but I'm not sure if they are to be used for Modbus TCP. So, my questions are: 1. How do I set up the Step 7 V12 program establish a connection with my client device? How can I verify this connection? 2. Once a connection is made how can I send and receive data to the client device? Do I use data blocks to hold the read data and the data to be written? Any help with this would be greatly appreciated! Thank you, BenB A couple of quick suggestions, easiest and first is to find out if your wireless device can be configured for profinet. If so, change to that protocol and download the GSD file to your portal. It is much simpler to communicate to a profinet client in the Siemens world. Second, in case the device does not support profinet, you can setup the S7-1200 plc as eitherMB_SERVER or MB_CLIENT by using the instruction block to match your needs. If you just need the server component, create a new OB/FC to support your banner modbus client, drag in the MB_SERVER component, read up on the help for the block, and set up the block interface tags. For the parameters, and just one client, maybe something like this: DISCONNECT = false (setting it to true disables communications) CONNECT_ID = 1 IP_PORT = 502 [default] - make it the same as the port your client will use MB_HOLD_REG = Pointer to a DB (and buffer length)containing the values you want the client to access for read/write. See help for details NDR -> NewDataReceived (bool)- your client sent new data - good for one scan DR -> ClientReadData (bool) - good for one scan ERROR & STATUS are used to diagnose your client connection and block configuration The client will have access to your digital & analog I/O via the standard Modbus function calls. When it reads / writes from/to the 4000x registers, your MB_HOLD_REG DB is used. Then you configure the client to access your plc's ip address at the above port (502:default). That's it. Then you just look for new data received, then act on the new data from the client, accept or reject it, and pass it on for processing as needed.
	science guy
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6/21/2013 5:06 PM	Rate (0)
BenB Advanced Member Joined: 3/5/2013 Last visit: 7/25/2024 Posts: 21 Rating: (0)	Okay I just talked to Siemens Support and I was going down the complete wrong path. I want the PLC to be able to read and write data to registers. For this I was told I need to use the client block. Can you please point me in the direction where I could find everything I need to know about the client block and how its used to access data. Thank you, BenB

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6/21/2013 5:40 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 12/26/2024 Posts: 12313 Rating: (2695)	Hello Ben; In Modbus/TCP a client polls one or more servers. So if you want to read and write to various CPUs they must be servers and your CPU must ne a client on Modbus/TCP. The MB_Client and related Modbus/TCP instructions are explained in this manual: STEP 7 Basic V12.0 And you will find a sample program from our friend Pegaia in this thread: Tips and sample program for MODBUS TCP Hope this helps,, Daniel Chartier
	Last edited by: dchartier at: 6/21/2013 5:40 PM
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6/11/2018 10:50 AM	Rate (0)
Wit_Moderator Moderator Joined: 8/21/2014 Last visit: 12/20/2024 Posts: 1035 Rating: (14)	New question published by HarePrasath is split to a separate thread with the subject Need help to commission Modbus TCP/IP. Best regards The Helping Hand
	My Forum is the place to personalize your profile, track your topics, and maintain content that interests you. Best regards Wit_Moderator
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