Mesta Automation. In this post you will find how to use n. Modbus with C and how to create a simulation enviroment to test your program with Modbus. Using%20Multiple%20DAQ%20modules_html_m51fc3908.gif' alt='C Source Code Serial Port Communication Visual Basic' title='C Source Code Serial Port Communication Visual Basic' />Other useful resources that you can find in this post are using a Modbus simulator. Creating virtual Com ports. Using this site ARM Forums and knowledge articles Most popular knowledge articles Frequently asked questions How do I navigate the siteUsing sniffer tools to debug the transmission. A Modbus TCP Client in C with another library. Getting NModbus. The C library I use the most when I need Modbus communication between pc and plcs or other components is n. Modbus. n. Modbus manages both Modbus TCP and RTU protocols, its well tested and sources are available. The new NModbus. 4 library on Git. Heres the part of the game where we get to talk code for a change. But first, lets discuss more noncode Yay First I want to talk about IP addresses and ports for. C Source Code Serial Port Communication Visual Basic' title='C Source Code Serial Port Communication Visual Basic' />Hub, but to compile it you need Visual Studio 2. C 6 features used. A. general provisions 177. Download demo project with source 81. Kb Introduction Serial communications is needed in several types of applications, but the Win32 API isnt a very easy to. IC InterIntegrated Circuit, pronounced IsquaredC, is a multimaster, multislave, packet switched, singleended, serial computer bus invented by Philips. You can also download from Nu. Get by searching for NModbus. The old library on google code has bugs check comments for more informations, please consider using either the new NModbus. The old library of n. Modbus is http code. Once you extract the sources you can open the solution file, located in the src folder. Sample code. NModbus contains many samples included in the source code. Once you open it, you can go to My. Sample project that contains many examples on how to read and write using different devices. You can check a how to video here https www. The two examples that I use the most are Modbus TCP and RTU, and an example of the code to use the library is this Modbus TCP. Tcp. Client client new Tcp. Client1. 27. 0. Modbus. Ip. Master master Modbus. Ip. Master. Create. Ipclient. read five input values. Address 1. 00. ushort num. Inputs 5. bool inputs master. Read. Inputsstart. Address, num. Inputs. Inputs i. Console. Write. LineInput 01, start. Address i, inputsi Address 1. Write. Multiple. Coilsstart. Address, new bool true, false, true. Serial. Port port new Serial. PortCOM1. configure serial port. Baud. Rate 9. 60. Data. Bits 8. port. Parity Parity. None. Stop. Bits Stop. Bits. One. create modbus master. IModbus. Serial. Master master Modbus. Serial. Master. Create. Rtuport. byte slave. Id 1. ushort start. Address 1. ushort num. Registers 5. read five registers. Read. Holding. Registersslave. Id, start. Address, num. Registers. for int i 0 i lt num. Registers i. Console. Write. LineRegister 01, start. Address i, registersi. Id 1. ushort start. Address 1. write three coils. Write. Multiple. Coilsslave. Id, start. Address, new bool true, false, true. Depending on the registers that you are going to read and write you have different methods, that will call different functions of the protocol, and that will return the results in 2 formats ushort or bool if you are reading multiple registers you will get array of ushorts and bools. ITDONOTWORKNModbus is supported by thousands of users, and you can find help on the NModbus google Group. Testing your program with a simulation The most common Modbus simulator is located at http www. This simulator provides both Modbus TCP and RTU protocols, and shows the content of the registers in the main windows so you can analyze the behaviour of your program directly in the tables of the simulator. Creating Virtual COM Ports to test Modbus RTU While its easy to use TCP to analyze the Modbus TCP on the host just create a socket with a 1. Modbus RTU or ASCII may require some hardware, like a null modem cable and 2 COM Ports. To avoid this you can download a null modem emulator called Com. Com open source, located at http sourceforge. Sniffer tools available for free If you need to analyze the traffic between two devices to see whats going on with your communication, there are two useful tools Wireshark is used to sniff ethernet packets and to decode the protocol. This tool can decode Modbus TCP protocol quite well and its also useful to debug the transmission. Free Serial Port Monitor is a serial port sniffer that can analyze the transmission between 2 COM Ports. Other Modbus TCP libraries While NModbus is the best choice, another Modbus TCP library is available at http www. Articles1. 62. 60Modbus TCP class. This library provides a client with some interesting features and its also useful for debugging the devices. How to video on NModbus. You can get the software configuration in the article. Serial Communication with Visual Basic. NETMore events can be executed on the same thread. This is the method used by the UI. All UI related actions gets. Each message has a name, which starts with WM Windows Message like WMCLICK, and it has an. This method has a similar name except that WM. On like On. Click. Very urgent messages like mouse cursor movements WMSETCURSOR and change of. WMACTIVATE and WMSETFOCUS are handled immediately, but most messages are linked together with other. It is possible to post up to 1. With the exception of the WMPAINT message, the WMTIMER. WMQUIT message, the system always posts messages at the top of a message queue by means of a. This ensures that a window receives its input messages in the proper. FIFO sequence. The WMPAINT message, the WMTIMER message, and the WMQUIT message, however, are. In. addition, multiple WMPAINT messages for the same window are combined into a single WMPAINT message, consolidating. Combining WMPAINT messages reduces the number of times a. The routine that reads from the message queue is called the message pump. Its basically an almost infinite loop. Get. Message as shown below. While Get. MessageMsg, 0, 0, 0. Translate. MessageMsg. Dispatch. MessageMsg. Once someone post a message, Get. Message returns with the value true. The loop then performs any message. Translate. Message. For example, the keyboard sends raw, virtual key messages like WMKEYDOWN. WMKEYUP. These virtual key messages contain a code that identifies which key was pressed or released, but not its. Shift or Alt key or the character Language. Translate. Message. WMCHAR. At last, the message pump calls. Dispatch. Message, which calls the message handling procedure Wnd. Proc of the control window specified in the message. Note that in case of one. Invoke, Begin. Invoke, End. Invoke and Create. Graphics, it is Whd. Proc of the control you have used in the call, which. Button. 2. Wnd. Proc in case of Button. Begin. Invoke even though Button. Wnd. Proc is basically a Select case construction, which calls the method associated with the message like this. Protected Overridable Sub Wnd. ProcBy. Ref m As System. Windows. Forms. Message. Select Case m. msg. Case WMCLICK. On. Clickm. l. Param. Case WMERASEBKGND Paint background. On. Paint. Backgroundm. Param. Case WMPAINT Paint foreground. On. Paintm. l. Param. Case. Case Windows. Forms. 20Thread. Callback. Message. Me. Invoke. Marshaled. Callbacks Empty the Thread. Callback. List of the control. Case WMCLOSE. Raise. Event Closing Old obsolete closing event. Raise. Event Form. Closing New 2. If Not Cancel Then. Destroy. Windowm. Wnd Close specified windowform. End If. Case WMDESTROY. Close all windowsforms. Post. Quit. Message0 Stop the message pump and terminate the application. End Select. Protected Overridable Sub On. ClickBy. Val e As System. Windows. Forms. Bulleted. List. Event. Args. Raise. Event Clicke Execute all event handlers for the Click event. Protected Overridable Sub On. PaintBy. Val e As System. Windows. Forms. Paint. Event. Args. Do whatever painting it has to do. Raise. Event Painte Execute all event handlers for the Paint event. The Paint. Event. Args specifies the Graphics to use to paint the control and the Rectangle, which needs to be. This is used in both On. Paint and On. Paint. Background. The 2. Windows. Forms. 20Thread. Callback. Message depends on the version 1. NET 1. 1 and 2. 0 for version 2. Windows. Forms. 20Thread. Schoolmate Save Game here. Callback. Message is described in more details in the control. InvokeBegin. Invoke chapter, but it. WMKEYUP and WMKEYDOWN. This means that if a program keeps sending such messages to the message queue, the window will not react on e. Therefore it is very important not to overload the message queue with these kind of messagesIn. NET 2. 0, the form closing event, which has only Cancel. Event. Args, is obsolete and replaced with the Form. Closing. event, which inherits from Closing, but also has information about the reason why the form is closed Close. Reason. property. Note that both events are raised before the form is closed so that it is possible to cancel the operation. Cancel true. Note that very urgent messages like WMSETCURSOR are send directly to Wnd. Proc bypassing the message queue. When the associated method like On. Click or On. Paint has done whatever it has to do, it must. These methods are called event handlers. Raise. Event. It is a very confusing name because it makes you. It doesnt. It just execute some event. You write some event handlers and when you want. The event has a name similar to the message and. Click. When the method and any event handlers. Dispatch. Message returns and the loop calls Get. Message again to wait for the next message. When Get. Message receives a WMQUIT message posted with Post. Quit. Message by means of WMDESTROY it returns with the. While loop exits. Let us take an example. If the user moves or resizes a window, some part of the window a rectangle, a region or. The method, which has moved or resized the windows, tells which part. Invalidate. However, there may be other UI events, which has occured before the window has been. Instead, Invalidate sends the messages. WMERASEBKGND and WMPAINT with the necessary Paint. Event. Args to the message queue. When WMERASEBKGND. On. Paint. Background method and when. Opengl Es 2.0 Sample Program here. WMPAINT reaches the buttom and there are no other messages in the queue except for WMQUIT as described previously. WMPAINT, WMTIMER and WMQUIT have lower priority than all other messages, the On. Paint method is executed and. Note that the time difference between background paint and. WMPAINT. When WMPAINT is finished, it will raise the Paint event, that is, execute all handlers. If you for example has created graphics with Create. Graphics, this graphics may need to be redrawn so you must. Paint event, which can do this. The On. Paint method and any other methods associated with a message are overridable so that they may be changed if you derive a class from. If you for example want to add something to the On. Paint method of the class Child. Class, which is derived from Parent. Class, you can. do it like this. Protected Overrides Sub On. PaintBy. Val e As System. Windows. Forms. Paint. Event. Args. The code you want to add. My. Base. On. Painte Call the original On. Paint method to do the rest and at last raise the Paint event. This is the preferred method rather than making some routines in Child. Class, which subscribe to the Paint event of Parent. Class. All applications or services, which use Child. Class, can then subscribe to the Paint event of this class if they have any graphics to redraw. Because the message pump is used to handle events for the GUI, it runs on the Main thread, on which all GUI objects. A typical GUI application, after doing some initialization in the Main method, will then start running. Because the message pump is an infinite loop it will run until the application closes, so the Main. The System. Windows. Forms. Application. Run method takes care of message pumping. If no form is specified, it begins. UI thread for the application or. If a form is specified, it also makes the specified form visible like. Shared Sub Main Called from the primary thread. Application. Enable. Visual. Styles. Application. Set. Compatible. Text. Rendering. Defaultfalse. Application. RunNew Form. Start the application and make Form.