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Modbus Slave & Modbus Master in S7 Refer to the Modbus Serial Pack v2 zip. Project Modbus v2 Manuals for drivers and hardware Preperation Preparation. To enable the Modbus functionality of the CP cards, you must do three things: Install Point to Point software from Install Modbus Master and Slave drivers from Fit the Modbus dongle to the rear of the CP Install the driver to the CP Preperation Summary of the GOULD-MODBUS Protocol The type of data exchange between MODBUS systems is controlled by Function Codes (FCs). The following FCs can be used to carry out data exchange bit-by-bit: FC 01 Read coil (output) status, FC 02 Read input status, FC 05 Force single coil, FC 15 Force multiple coils.
The following FCs can be used to carry out data exchange register-by-register: FC 03 Read holding registers, FC 04 Read input registers, FC 06 Preset single register, FC 16 Preset multiple registers. Gould-Modbus Summary of the GOULD-MODBUS Protocol It will save considerable time and frustration to have a good idea upfront of the mapping of Modbus data to S7 data. The Modbus slave will define the function codes to be used by virtue of the fact that specific data is held in specific Modbus registers. Function Code Modbus Address Range Access Output Coils Function Codes 01, 05, 15 Read/Write Input Coils Function Code 02 Read Only Internal Registers Function Code 04 Holding Registers Function Codes 03, 06, 16 Gould-Modbus Configure the Hardware as Modbus Slave With the software installed you can now open the Hardware Configuration and configure the CP341 in your rack. Double click the CP to open its properties and click on the Parameter button. The Point to Point configuration software will now open. From the drop down box at the top left, select Modbus Slave as the Protocol.
Next double click the Protocol icon in the middle of the screen. S7-300 Slave Configure the Driver. You are now presented with a number of tabs.
The first tab 'General' shows the driver versions in use. This is for information only. The second tab 'Modbus-Slave' allows you to define the communications properties of the system, baud, stop bits etc. S7-300 Slave Configure the Driver.
On the tab labelled FC01, 05, 15, you can enter the Modbus address ranges to be mapped into M area, Outputs, Timers and Counters. If any areas are not used, enter 0. S7-300 Slave Configure the Driver. On the tab FC02, you can define the mapping for M area and Inputs to be read from.
S7-300 Slave Configure the Driver. On the tab FC03, 06, 16 you only need to enter a DB number. These function codes use the address range starting from Modbus address The DB number specified is the start DB of a range of DB's that are generated by the user and must be 512 words long. If your Modbus address is say 40513, you would need to generate another consecutively numbered DB of 512 words long. Modbus address would be the first address in the second DB (word 0 of the second DB, the 513 word in total). S7-300 Slave Configure the Driver. The tab labelled FC4 is configured in the same way but for the address range.
S7-300 Slave Configure the Driver. The next tab is labelled 'Limits'. This is where you can define the range of DB's, Memory and Outputs to be written to by FC05, FC15, FC06 and FC16. If you were to use the Modbus address 40513, this would reside in the second DB at word 0.
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Open Source Modbus Library
You would therefore need to set the limits here to DB1 and DB2 (assuming DB1 is the DB selected for use by FC03, 06, 16). This is similar for M and Q areas.
The final tab defines any electrical properties. S7-300 Slave Download Hardware Configuration and Modbus Driver. Save and Compile the Hardware Configuration then download to the controller. Once the configuration is downloaded we can install the driver to the CP. To do this you must have an online connection and use the Load Drivers button from the Driver Parameters (as we have just configured). S7-300 Slave Movement of Modbus Data between the CP to the User Program. Now the driver is configured.
Alvin and the chipmunks the squeakquel 720p torrent download. It knows what to do when it receives a Modbus telegram – read or write data to or from a specific Simatic area. Now that the Modbus data can be interpreted by the Modbus driver on the CP341, we need to move the data from the CP to the CPU of the PLC.
This is done by use of FB80 MODB341. This block can be found in the library entitled 'Modbus'. The block is called as part of the cyclic user program via OB1. It needs to know the logical address (LADDR) of the CP341 from the hardware configuration which can be found by highlighting the CP in the rack in Hardware Configuration. The address will be shown under the I-address column of the bottom half of the window. S7-300 Slave Movement of Modbus Data between the CP to the User Program. Block Dependencies: When you add the FB80 block to the user program, you will be required to generate an Instance Data Block.
BEFORE generating this block, ensure that the FB7 and FB8 blocks are also present in the blocks folder (these are found in the same Modbus library). This is because FB80 uses these blocks to communicate with the CP.
S7-300 Slave Movement of Modbus Data between the CP to the User Program. OB100 – Startup OB The only coding that the user must perform is in OB100, where we set a bit on and a bit off to initialise the FB on start-up of the CPU, used at the parameters CPSTART and CPSTARTFM. S7-300 Slave Movement of Modbus Data between the CP to the User Program. OB1 – Main Cyclic OB Call FB80 in OB1 and assign addresses for status reporting. Also assign the CPStart and CPStartFM bits generated in OB100.
Download all program blocks to the controller and test!!! S7-300 Slave Configure the Hardware as Modbus Master To configure the Modbus Master, we start in Hardware Configuration. Perform the same steps as for the slave (selecting Modbus Master as the Protocol) and click on the Protocol icon in the middle of the screen. S7-300 Master Configure the Driver. Here you have three tabs.
The first, 'General' identifies the driver version, as in the slave. The second, 'Modbus Master' is where you define the communications properties, stop bits, baud etc. S7-300 Master Configure the Driver. The final tab defines any electrical properties.
This is the hardware configured for operation. We must now send and receive data to/from the CP341.
S7-300 Master Movement of Modbus Data between the CP to the User Program. OB1 – Main Cyclic OB In the cyclic user program we must call two blocks, PSNDRK and PRCVRK, found in the Modbus library. The Modbus Master will send a request for data to its slave (reading values) or simply send it data (writing). S7-300 Master Movement of Modbus Data between the CP to the User Program. The send block is used to send a number of bytes that are structured in a specific way and populated with specific data, depending upon the function code to be used. For example, FC03 requires the first byte to contain the slave address, the second byte to contain the function code number, the third and fourth bytes (DBW2) must contain the Modbus start address and bytes five and six (DBW4) contain a value representing the number of registers required.
S7-300 Master.(All of the structures of data for the various function codes can be found in section 5 of the Modbus master manual). Movement of Modbus Data between the CP to the User Program. OB1 – Main Cyclic OB You will need to define a DB that can be used to receive the data into.
You call the receive block, and populate its parameters similarly to the send block, telling it the LADDR of the CP341 and the DB to which the data is to be received. S7-300 Master Movement of Modbus Data between the CP to the User Program. With these blocks now configured, you can download to the hardware and you should have a working Modbus master. Of course, the blocks will need code writing around them for timing the send and receives and also error handling, but I recommend using a VAT (variable table) to manually trigger sends etc until you are happy that the system is functioning. This way you are in control of the requests and also the data that is sent.
S7-300 Master S7-400 Modbus Master and Modbus Slave The configuration is similar when using the S Differences include the possibility to install two interface modules to one CP441-2, which can be configured independently for different functions. These interface modules are fitted to the front of the CP, with the type dependant upon the electrical connection to the system (RS232, RS485, RS422). The driver configuration is identical to when using the S7-300.
S7-400 S7-400 Modbus Master and Modbus Slave There are differences in the blocks used for both slave and master functions in the S7-400. Firstly, the slave uses block FB180 MODB441. This can be found in the same location as the block used in the S7-300. Secondly, the master uses different blocks to the S The S7-400 uses the System Function Blocks SFB12 and 13 (BSEND and BRCV).
S7-400 S7-400 Modbus Master and Modbus Slave The main difference with both the master and slave blocks is the requirement of a connection between the devices. This connection is configured in Netpro and the ID of this connection is entered as a parameter to the send and receive blocks. The connection type is Point to Point. Once a new connection of the type Point to Point is added to the configuration, you can view the properties of it. Here you can set the CP to be used and select which of the CP’s interfaces are to be connected. You also find the connection ID, whose value needs to be entered to the send and receive blocks. S7-400 Diagnostics Diagnostics Sometimes you may have configured the system but devices do not communicate in the manner you expected.
Things may appear to be healthy but data is not being successfully transferred. If this is the case then you have a number of options available. The first place to check would be on the block calls. The blocks will generate status and error information. Secondly, you can check the Module Information of the CPU and CP for any diagnostic entries.
Error codes generated on the block calls and in Module Information can be found in the manuals included in the Modbus Serial Pack. A further option is to monitor the network using a network analyzer. This will enable you to see the raw data present on the network media and determine if it is present and correct.
You should be seeing telegrams with the format matching that described in chapter 5 of the Modbus master manual, depending upon the function code being implemented (byte 1 should contain the slave address, byte 2 should contain the function code etc). Diagnostics Multipoint Connection Details. RS422 Multipoint In the RS422 mode CP341 and CP441-2 can only be used as a Master“ Multipoint Connection Details. RS485 Multipoint Multipoint Connection Details. The following applies for both modules:.
GND (PIN 8 by CP341 / CP441-2) must always be connected on both sides. The casing shield must be installed everywhere. A terminating resistor of approx.
330 Ω is to be soldered into the connector on the last receiver of a node sequence. Recommended cable type: LIYCY 3 x 2 x 0,14 R(A)/R(B) and T(A)/T(B) twisted pairs. A wiring with “Stub“ is not allowed Multipoint.
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Great article, are you familiar enough with NModbus (or the modbus protocol in general) to know if it has the ability to be event-driven. That is, to not have to user a timer or manually poll for data from a client PLC?
I know an OPC Server is the ideal solution, but for only a couple PLCs, it’s too expensive. Finally, I know that the NModbus site was hacked and the documentation was lost.
However, the author said the documentation could be recovered if rebuilt from the Nant task in the source code. Perhaps you could re-host the documentation, or that could be another article! I know a LOT of developers are looking for it. Cheers and keep up the good work. Hi Derek, there are no problem in hosting the documentation of nmodbus, but it just consists in 8 examples that can be found inside the source code (“MySample” folder).
About the event-driven communication, it’s just a layer above the syncronous communication. To develop an asyncronous communication you need to have a thread dedicated to polling the modbus device. This thread listen to external calls from the application and executes reads and writes to the plc. When data are ready it fires a “DataReadyEvent(EventArg data)” to all subscribers.
The problem of this architecture is that it requires a lot of code that add no value to the application itself, because once you can write a multithreaded application, you can just extract your data from the communication thread, saving yourself from the pain of event-handling, subscription and memory leaks. There is an example of hmi in my that shows a basic structure of multithreaded app.
Hi, I’d like to rephrase Dereks question above regarding event-driven. I stumbled upon S7.net (originally hosted at: which is dedicated for Siemens PLC and is now continued at: I belive this library uses modbus (but not sure). However it also lacks the event driven communication. I understand that you can create a thread that polls the PLC and generates the event when it detects that data is changed. However the optimal solution would be that the PLC (or modbus device) sends the data itself upon change. Does such mechanism exist for the modbus protocol? If your PLC (or another modbus device ) is a master, so your PC application will be a slave.
In this case the PLC(master) can share is information when ready to do it, and the PC(slave) only have to receive it. The NModbus supports this “kind of feature”, it can be configured as Slave or Master (ASCII, TRU and TCP/IP). I think you must read something about the Modbus Protocol first. The Modbus protocol is very simple to understand, so you don’t need so much time to do it. After that you will use the NModbus library mutch better. (sorry for my bad english ? ) Best regards.
Hi, Thanks for your answer. I Read about the protocol for about 5 minutes now ? So from what I understand you have a master and a slave configuration. The master sends out requests which the slave node(s) reply to. Typically a polling scenario.
In order to get data upon events I have to set up the PLC as a master which writes to the PC as a slave. This would require some kind of extra logic (PLC program) set up in the PLC which I want to supervise. With TCP-modbus it is possible to setup the PC and PLC as both master and slave (on different connections).
Not the general simple solution I was looking for so I think if I want an event driven communication it’s better to go with some OPC-solution which has already solved what I’m looking for. Do you know how this is solved under the hood of the OPC-server? Is the OPC server polling the device? Hi Eric, probably you are confusing the two libraries, but S7.Net use S7 protocol, nModbus use Modbus protocol (that depending on the physical cable can be Modbus TCP (ethernet) or Modbus RTU (RS 422 – RS 485). S7.Net use Profinet (or Industrial Ethernet, don’t remember that good) and it’s derived from LibNoDave that can communicate both with Profinet and MPI. To use nModbus you need to add the Modbus libraries to the plc program.
About Master and Slave, think like internet: a website is the Master and your pc that browse the site is the Slave. The master choose who and when a slave can talk, but it’s up to the slave to choose what he needs from the master, so you need no extra-coding on the plc part if you just need to read/write values on a DB. Both MPI, Profibus and Profinet are multi-master protocols, this means that when a master did what he needs, he pass the token to the other master, and so on. Modbus RTU is not multi-master, Modbus TCP is multi-master. Cisco 7921g usb driver windows 7.
About S7.Net, you can check a working hardware configuration sample in this thread: this has been tested. About the event-driven architecture: or you implement your own in your polling thread, or you use it as is with an OPC Server. Hello again, I’m greatful that you are answering my newbie questions. The background for the question is that I found the S7.net library. Tried it and worked well. Since there are no real support for this library I wanted to find more information regarding how it worked under the hood (which protocol was used and so on).
I found this discussion: Which to me indicated that the library used modbus TCP for communication. I kind of doubt that it is derived from LibNoDave after reading this discussion: And by looking at the source it seems like it’s really implemented in C# all the way down to the byte communication. But it may very well use another protocol than modbus and I’m quite eager to find out which protocol. We did not set up anything (if I remeber correctly) on the PLC side to be able to access it using S7.net.
Yes you can use C# and NModbus to control your drive, if the serial port is a RS232. If it is a RS422 or 485 you need extra-hardware. To communicate with Modbus through the serial port you need the Modbus RTU protocol, already included inside NModbus. You just have to know what register you need to read/write, and write the values that you need.
Probably you need to do this independently if you use a PLC or a PC. However It is reccomended to use real-time OS to control motors, and Windows is not such OS. Hi Mesta, Thanks so much for your information. I am new to Modbus, and have been read myself like one week about it. I am working one one project which needs to realise the Modbus RTU master function in C#, in order to read the data value from the slaves.
I found that your library is the best, but.my problem is that: Can you explain to me the structure of your library? In fact I do not know which parts are the library excatly. It has so 6 projects when I open it in Visual C# 2010 some other I can not even open Thanks a lot. Hope you understand what I mean! Hi mesta, Sorry for bothering you again. I would like to ask that, I want to make one software application which will read and display the Modbus RTU communication register values.
How can I do it? Should I create a IModbusSerialMaster first, then send message to slave? I want to display all the regoister values when I connect my software and PLC. Which is the function to read from RTU slave? Thanks a lot. Please even give me a general hint is also very appreciated. As I am new to this field, but need to get the work done still.Thanks!
Hi mesta, thanks for answering. But they are too much for me I do not understand what do you mean. Can you explain little bit in detail? In fact what I want is: user enter slave ID, comport number, and baudrate then I have one button which will connect to the corresponding port automatically. Then the value of the registers should be displayed in datagrdiviewI get got stuck in this connect button.You gave is a very good library, but I do not know where should I start to do. Hope you understand, Also you know any Modbus RTU slave simulator?
Hello everybody, i have just download the NModBus library to read some Holding Registers of a device, in my c# 2010 express solution explorer added the reference to the modbus.dll from binary/net of the extracted folder, added all namespaces from modbus ie using modbus.data, using modbus.io and so on. Then also added ftdAdapter.dll and wrote a small code to read holding registers using modbus RTU as explained by mesta at this page. But my project is not able to build.
It says namespace name ‘Modbus’ could not be found (are you missing a using directive or an assembly reference? U guys are way ahead this issue, please drop me a line of advice. Got out of obstacle but stuck at the next. Well, I have a Modbus tester from namely “Modbus tester ”, this is something I have used for years. I have made some usual settings inside this software (protocol = Modbus RTU, pairity = even as per my device and so on).
Starting address address = 3901, no of registers = 2, type of reg = holding and so on. This Modbus tester software reads my device correctly and also sets the display correctly in binary / hex / float etc.
This is perfect. But when I run the same settings using same converter same device with Modbus RTU holding register read (start address = ushort 3901 and no of reg = ushort 2, device address = 1), my c# code throws an exception saying “Function code 131, exception code 2, the data address received in query is not an allowable address ”. For the time being this is beyond me, how come NModbus driver is interpreting the same working address as wrong? Anybody has any clue? Please drop me a line.
Mesta u r very correct. Memory I was reading were meant to be read as a block but I was trying to read only 4 locations from top out of 20, which was giving me a CRC error. Next, a location named 3901 in the manual = address 3900 in the c# code. I was able to fix the problem by looking at the response in the serial port monitor software.
Then I hooked my Oscilloscope in Rtx of com port, that too was helpful. Now NModBus C# API is ROCKING in my shop floor, thanks a lot for ur expert advice.
Hi Mesta i have had started long time ago from here now i have written my own modbus implementation for S7 300 / 400 / 1200 and also have written a small library using tcp ip fetch and write service to talk to above mentioned PLCs and they all work as expected. There is one thing i am still strugling with and that is drawing line circles and rectangles on the winform. While developing a SCADA one has to show pipelines and stuff, is there any windows OS paint like program using which i could draw those static graphics on winform? I have been working with this library for almost a year and have a problem that I can’t solve. In searching through the NModbus discussion groups, it looks like other people have this problem as well and it hasn’t been resolved, (see and ). The problem is related to shutting down the TCP ports when the ModbusTcpSlave is disposed. If I dispose of the slave, the ports are still active.
If I iterate through the Masters collection and manually close the clients, then an exception is thrown (either IO Exception or Object Disposed Exception) that I haven’t been able to catch, so the software simply crashes. This seems like a bug within the class library since the software is still trying to communicate on the port after the clients have been closed and the ModbusTcpSlave has been disposed.
The only way I’ve found to close these ports is to kill the software altogether and start over. Is there a recommended way to close the client ports? This is a real problem that may require my client to walk away from the software altogether. Any help would be appreciated. Thanks for your quick reply; however, properly closing the ports is not the problem. The problem is that as soon as they are closed, an ObjectDisposedException is thrown from NModbus.
In reviewing the NModbus source code, this is what I think the problem is: in class ModbusTcpSlave, in the method AcceptCompleted, a new master is created when a client connects and a corresponding event handler is added for masterConnection.ModbusMasterTcpConnectionClosed. The method linked to this event handler is supposed to remove the master and close the socket, but it is not being called. So, if I call the Dispose method on ModbusTcpSlave, the slave is shutdown, but the master ports remain open. I verified this using NETSTAT from a command line.
If I manually close the masters, they are closed, but the event handler created when the connection was first made is still active and polling, so the software immediately throws the exception and kills my software. This is a NModbus problem because only NModbus can unsuscribe from the event handler.
I have no way to control this event handler from my code. I have tried to catch this exception, but haven’t been successful.
This is a problem in my software because if the ModbusTcpSlave needs to be shut down and restarted (e.g., in the case of a communication failure), then when it is restarted and the master reconnects, then the original ports remain open. Eventually, those open (but now dead) ports are causing the software to crash. I think a simple solution would be to unsubscribe from the masterConnection.ModbusMasterTcpConnectionClosed event in the ModbusTcpSlave.Dispose method. However, I would really like your opinion on this matter, especially if there is a way to properly dispose of the slave and master connections. I use DAQFactory Monitor: Tx (10:02:57.706): 062 003 000 002 000 020 225 010 Rx (10:02:57.710): 062 003 000 000 000 000 000 000 000 020 230 003 082 000 010 003 082 005 070 007 058 009 046 011 034 013 022 015 010 016 254 018 242 020 230 028 038 036 012 043 166 051 179 221 053 When i use nModbus4: Modbus.IO.ModbusSerialTransport Write – TX: 62,3,0,3,2,0,20,255,10 Modbus.IO.ModbusSerialTransport ReadResponse – RX:62,3,0,0,0 – and that’s all.
I am get only 5 registers. When i go to “Modbus.cs” and change “public const int MinimumFrameSize = more than 6;” i get new message “Message frame must contain at least (6) bytes of data”. Where is the problem? I can’t understand how with that function you obtain those values. I used your code and I got the expected message. The request frame is “Node” / “Address” / Start Address #1 / Start address #2 / N° of registers #1 / N° of registers #2 / And you have not six, but seven bytes.
Also you are getting function code 3, that it’s “Read holding registers” but you actually wrote ReadInputRegisters. And infact in the first post you obtained a 62,4,0, that it’s the correct number of the function. Now if you are trying to read holding registers with the function that read inputs, you obviously can’t. What you have to do is to go step by step in the sources and understand what’s going on when you create the frame.
Also if you modified the sources, or you have a suspect that they can be modified, I suggest you to go back to the original version. If you need some modbus documentation, you can go here. I experienced a similar issue today like in the above comment: “I am getting IOException Checksum Failed to match 62,4,0!= 62,4,0,0,2” I receive a “valid modbus response” with slave-adress, functional-code, correct number of following registers, the registers contain the values I expect and the crc-checksum is correct.
(Even calculated it on my own with the Utlity provided by NModbus4) But.somewhere inside the library. (i assume “ModbusMessageImpl”-class), a few bytes of the response get dropped / get lost. And therefore, such exceptions arise. After some hours I was not able to locate the cause for this.
In my opinion, the response is valid, but NModbus4-lib is doing something wrong! Sadly, noone is reacting to such issues, see for example here: (This question is from someone else, not me). Hi, I made a Windows Form to communicate via nmodbus with a slave.
(ASCII Mode). Reading works fine and I can store the Registervalues in an Array and print them in Labels. Now I want to write a Register. And the slave will send a respond message (Ok or failed). With the terminal programm of the sample it works well.
(I think ReadRequestResponse in ModbusAsciiTransport is writing it to a byte called frame). I want to use the responded message from the slave in a Label. So I can see in Form1 if I the slave accepted the changes or not. How can I implement this?
Thanks for the Support here. Thank you Mesta, I know that the normal Response is the same query that the master wrote. But if the writing fails it responds with another message.
So it would be nice to read the message. But I if it is not usual to read the Response I don´t need to read it. My Problem is that after sending the write request I want to close the port again. But the program throws me because the Serialport is busy. I thought the best would be to read the responding message and then close the port. But it would be possible just to wait some time till it is not busy anymore and then close it.
(Maybe with a timer) What is the best way to deal with this problem? I think everybody who works with Modbus has to solve this So there should be a common way to do it. Thank you so much for responding so fast and for all the help. Hello Mesta, I have read forums entries here from 3 years ago.and i dont seem to find a solution for my problem.
ANd so im entering into the loop. I am into automation project right now. Need to control a despatche oven machine. Its controller based system that applies a MOdbus protocol. Last week I downloaded the Nmodbus project. I had it working (perfectly) but only with PLC modbus simulator as my slave. My boss was glad to hear that i have control now with the machine.But, it wasnt the case when i connected with the real machine.
I set and followed all the configuration settings if the serial port. But when the code run into these line var values = master.ReadHoldingRegisters(slaveId, startAddress, 1); textBox3.Text = values0.ToString;.the program got in to “stalled” status. I had to close it down on the task manager. Additional info: There is a third party software running in the master pc that seems to have no problem using the modbus. It can actuaLLY read out data from the machine.
And I think to rule out some probelem in the machine itself. Hope to hear from youand to anybody who reads this ? Thanks, Joseph. Man you’re fast! I was expecting ur reply tomorrow. I was only given until tomorrow to figure out the Modbus communication.so i must be able to connect it. The controller is a Protocol3.
It supports Modbus RTU. Currently there is software running at configuration 9600,None,8 bits, 1 of the serial port. There is no problem at all, only the software is limited in functions. So we have to design a system that can automate the machine based on the company’s data architecture. Meaning it has to be connected with our manufacturing system where we can automate and control. Because right now we have to depend on the operator (human) which has been proven to be a source of lots of problems in the production floorAnd i just couldn’t even connect.
? The machine has no HMI, but it has a small LCD display with a small panel to make the settings. The third party software serves as the HMI. Let u know tomorrow. Thanks for your quick reply I am able to read the register value using “Modbus slave” software. But I couldn’t get those values in my program. Getting Checksum error.
I used the same slave address, baud rate, data bits and parity. Please tell me which function I have to call for the following scenario. My PLC is master and my PC is slave. Conected using RS485 to USB. But, StartModbusAsciiSlave; function isn’t defined. Whether I have to call StartModbusSerialAsciiSlave or StartModbusAsciiSlave Please share if any tutorial for modbus ASCII mode. My Application connected successfully with Telnet Server using TCPClient.
But while ReadingHoldingRegister from Telnet server I am getting following Error’s in different scenario. An existing connection was forcibly closed by the remote host 2. The requested address is not valid in its context 3. Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. The operation is not allowed on non-connected sockets. Note: Telnet Server is a device not a server i.e We can’t run TCP listener R Muruganandhan.
Hello David; I always presumed (not to say 'assumed') that Siemens did not support Modbus/TCP. Your post made me look a little deeper, and here is what I found on different Siemens webpages: Siemens websites on Modbus/TCP options: Flyer: Manual: You can obtain further information on this topic at the following address: Siemens AG Industrial Solutions & Services Information Technology Plant Solutions Werner-von-Siemens-Str. 60 D-91052 Erlangen Tel.: +49 91 31 7-46111 Fax +49 91 31 7-44757 E-mail: [email protected] Internet: If you are located in Amwerica, note that you might have trouble getting pricing and delivery info from your local rep; divisdion of certain Siemens markets and products may be strange to understand for us laymen.
In that case you would need to deal directly with the European providers, possibly using a Simatic Card (prepaid buying cards used for certain transactions over the web). Thanks for the new comm. Oppertunities, Daniel Chartier. Daniel, Thanks for tracking that info down, it should help it trying to purchase this library. My Siemens Rep. Said, 'Since it's very pricey for one thing but also it's not readily available/supported here in the US.'
He went on to say there might be shareware versions meaning customers had made there own custom implementation of Modbus TCP. Its very feasible to write a custom protocol with FB50 and FB60. I was hoping someone else has been down this path and might have a working example to share. I really only need to implement a simple class 0 master or slave. The Open Modbus/TCP you describe has a few problems. It uses the AGSEND and AGRECV Siemens blocks, which in turn use SFC58 and SFC59.
In any complete TCP/IP transaction, these limit the length of any transfered data to 240 bytes. (Some of the CPs are stated to transfer more, but they do this by splitting the data into 240 byte transactions). Unfortunately Siemens do not seem to have implemented the IP protocol fragmentation scheme correctly, so each of these transactions will appear (to, for example, a Windows socket) as complete and separate. The maximum data length of a Modbus RTU message is 255 bytes, and the Modbus TCP header adds a further 6 - i.e. Greater than the 240 limit. If you are sure that you will never have more than 240 characters (which is 234 if you exclude the ModbusTCP header) then you are probably OK. If you are not certain, then you should take further advice.
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