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Modbus TCP class

Stephan Stricker

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23 May 2014CPOL 1.7M   60.4K   154   171

A Modbus TCP class.

The project has moved to GIT

https://github.com/stephan1827/modbusTCP

Please download and ask questions from there.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Written By

Stephan Stricker

Systems Engineer

 Germany

This member has not yet provided a Biography. Assume it's interesting and varied, and probably something to do with programming.

Comments and Discussions

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Re: problem with writing to Siemens PLC holding register with MODBUS TCP Stephan Stricker21-Dec-12 22:55 Stephan Stricker 21-Dec-12 22:55  Anne, Can you please download wireshark and add some traces? This will tell us what data is sent and the response from the plc. Stephan Re: problem with writing to Siemens PLC holding register with MODBUS TCP Member 94111612-Jan-13 9:16 Member 9411161 2-Jan-13 9:16  Hi Stephen, Thanks for your reply. As you suggested, I tried wireshark, and was using your MODBUS tester to test the communication. It seems that for writing multiple registers, the start address couldn't go over 84. If start address is bigger than 84, for example 85, PLC will give out exception. I saved the file and screen copy, but not sure how to attach it to this message. and I am new to it, maybe did something silly. Thanks, Anne Re: problem with writing to Siemens PLC holding register with MODBUS TCP Stephan Stricker3-Jan-13 4:12 Stephan Stricker 3-Jan-13 4:12  Anne, somewhere in the Siemens PLC there must be a configuration where you define the size of your Modbus buffer. It seems that you buffer is 84 plus the amount of data you try write. When you write to addresses below 84 do you see the values in the Siemens PLC? Stephan Re: problem with writing to Siemens PLC holding register with MODBUS TCP Member 94111612-Jan-13 12:16 Member 9411161 2-Jan-13 12:16  I am kind of get it. In my case, if the second 100 bytes are for writing, then the start address should be 50 instead of 100. Is it right? thanks, Anne Re: problem with writing to Siemens PLC holding register with MODBUS TCP Andrea Feduzzi14-May-13 6:12 Andrea Feduzzi 14-May-13 6:12  did you resolve the problem!? If yes could you contact me at andrea.feduzzi@gmail.com or post below. I use siemens s1200 series thanks Can't Write Coils KitaMenang22-Nov-12 3:08 KitaMenang 22-Nov-12 3:08  Hi thanks for the code but i am having a slight problem Connection to the PLC is succesful but i cant seem to write coils. I am using your test application. Problem: The Start address is at 0 The Size is 8 Bytes I can write the first coil but when i try to write the second one it does not work I have tried writing multiple coils but still it does not work. May I no why this is happening and how i can solve it Re: Can't Write Coils Stephan Stricker22-Nov-12 3:17 Stephan Stricker 22-Nov-12 3:17  What error message do you get? Can you create a network trace with Wireshark? convert error tomasz25616-Nov-12 2:28 tomasz256 16-Nov-12 2:28  I have Visual Studio 2008 and Framework 3.5 SP1 after convertion, a have error 'no overload for 'MBmaster_OnResponseData' matches delegate 'ModbusTCP.Master.ResponseData' and others which Framework or version VS should be correct for compile without convertion? Re: convert error Stephan Stricker18-Nov-12 8:44 Stephan Stricker 18-Nov-12 8:44  The framework that I used was 2.0 but it should work with newer frameworks as well. The message that you get sounds like the number of parameters that you define ResponseData function is not correct. Stephan Can't open with free ms tools chris wedgwood26-Oct-12 4:09 chris wedgwood 26-Oct-12 4:09  I am not familiar with the visual studio tools, but I expect to be able to figure it out. However, I cannot open the solution with the free download Visual Studio Express (VB and C# installed) Can someone please give me a step by step on how to get started. Thanks. Re: Can't open with free ms tools Stephan Stricker18-Nov-12 8:45 Stephan Stricker 18-Nov-12 8:45  The source code should work with VS2010. What exactly happens when you try to open it? Re: Can't open with free ms tools chris wedgwood18-Nov-12 23:11 chris wedgwood 18-Nov-12 23:11  Ah, I fixed it. I was confused about which tool to use, and ended up with the 2012 desktop version, which works really well. Thank you ! Unable to Read, able to write alexamex16-Oct-12 6:38 alexamex 16-Oct-12 6:38  Hi, Thanks for this amazing API. Btw, I am able to write, but unable to read. No error message given. Did someone have that bug too? Thanks. Alex Re: Unable to Read, able to write Stephan Stricker16-Oct-12 7:15 Stephan Stricker 16-Oct-12 7:15  If you dont see an error message everything should be fine. Can you create a Wireshark trace from the data exchange and post it here? Any VB.Net synchronous mode examples available? Member 90645551-Jul-12 2:25 Member 9064555 1-Jul-12 2:25  I am testing function code 23 using synchronous mode. I can get the command to work but am having some difficulity getting my code set up to check for exceptions, I wanted to make sure the command was executed sucessfully before processing the results. I was hoping to find a simple code sample that would show the proper way to check for exceptions. It works globalpositioning14-May-12 6:06 globalpositioning 14-May-12 6:06  Stephan, I tested your software in VisualStudio2008 and after some conversion processed by the environment, I compiled and worked perfectly without modifications. I tested this software with a Modbus/TCP simulator from a company called EmbeddedIntelligence. Excellent job. Disconnects and holding registers value displacement harizhent16-Mar-12 4:31 harizhent 16-Mar-12 4:31  Hi, Thank you for shearing this code. I just compiled your sample code and i'm having few problems... few seconds after connecting and reading any data from HMI(Beijer iX), program disconnects(connection is lost). Then i try read holding registers from HMI(40001-40005), the results i get is like that.. http://imageshack.us/photo/my-images/269/deletelt.png/[^] data is correct but it is misplaced or something like that.. thank you. Re: Disconnects and holding registers value displacement Stephan Stricker20-Mar-12 2:51 Stephan Stricker 20-Mar-12 2:51  The values may look wrong because you read them as BYTES. Most analog values in modbus are WORDS so if you changes the selection at "Show as" to word it should be correct. Some slaves also have a communication heart beat. This means that once you connect you have to send a reuqest every x seconds. Otherwise the slave will auto disconnect. My vote of 5 Nikolay Ugorliev24-Feb-12 1:27 Nikolay Ugorliev 24-Feb-12 1:27  Great job! Modbus says error: Illegal function! xeroxvrey6-Feb-12 5:57 xeroxvrey 6-Feb-12 5:57  Hello, I get this error: (Modbus says error: Illegal function!) When working with a simulator called "Modbus Slave", but if I taste with another called "mod_RSsim" works perfectly, the same error I get when I connect to a device physical Modbus TCP. Is it a compatibility issue with some other Modbus protocol? Re: Modbus says error: Illegal function! Stephan Stricker6-Feb-12 6:07 Stephan Stricker 6-Feb-12 6:07  The error means that you try to call a function code that is not supported by the slave or you try to call a function to an address that does not allow this function. This error comes from the slave. Re: Modbus says error: Illegal function! xeroxvrey6-Feb-12 10:27 xeroxvrey 6-Feb-12 10:27  Thanks for the reply, I am using the sample application (Sample Modbus Common), without modification, then I don't think the error is to call a function or bad register, because the application properly written on the register configured by pressing the "Write multiple register - Write single register - Write multiple coils - Write single Coil" but no function of reading, in any of them I get this error. As I mentioned before this only happens to me with the simulator (Modbus Slave[^]) and the actual device, with other simulator (mod_RSsim) all functions are working properly. What can be? Modbus TCP Class not working Joseph Frippiat23-Jan-12 1:50 Joseph Frippiat 23-Jan-12 1:50  Hello, I am not able to make the code work. When I try, with the sample application, to read 32 coils starting at address 1000 (with the button <read coils="">, I always get empty data (zeroes everywhere). In the OnReceive function, id and function are equals to zero and tcpAsyClBuffer is filled with zeroes. I checked in the slave Modbus, it receives the request and it answers it. I don't know where the data are going? Thanks for any answer, Joseph Re: Modbus TCP Class not working Stephan Stricker23-Jan-12 1:56 Stephan Stricker 23-Jan-12 1:56  Joseph, could it be that the data simply is zero? You can double check with Wireshark what data you request and what data you receive in the response. Also keep in mind that coils are output data. If you want to read digital input data you have to use discrete inputs. Stephan Re: Modbus TCP Class not working Joseph Frippiat23-Jan-12 2:13 Joseph Frippiat 23-Jan-12 2:13  Stephan, the function code returned in the answer can not be zero. It must be equal to 0x01 if there is no error or 0x81 if there is an error. I do not understand why it is zero. It seems that when the event OnReceive is fired, the tcpAsyClBuffer is not filled. Joseph

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