The Try-Catch surrounds the port open function to flag system errors, for example that the port does not exist. GetPortNames A procedure to send a frame in cmd,data format out the port. Write buffer, 0, 2 End Sub To send one byte, use this. Write buffer, 0, 1 To read one line blocking. ReadLine To read one byte blocking. ReadByte serial-port-vb. Read buffer, offset, count For receiving data at unexpected times, use the DataReceived event. This is a bit tricky because it runs in a different thread and requires a handler.
The dispatch code is generated when a device driver is loaded. If more device drivers want to use the same hardware interrupt, that is, same interrupt vector, the interrupt objects are linked together in a chain. Windows does not depend entirely on the hardware interrupt priority. It has its own priority system with 31 interrupt request levels IRQL. Windows uses IRQL's for implementing a priority mechanism similar to the one in the interrupt controller. If IRQL is 0, all interrupts are enabled.
The dispatch code in the interrupt object calls KiInterruptDispatch if there is only one interrupt object for this vector. If there are more objects it calls KiChainedDispatch. KiInterruptDispatch or KiChainedDispatch raises the IRQL to the level specified in the interrupt object to block for all other interrupts with the same or lower priority. The ISR reads short information like status etc.
The ISR acknowledge the interrupt. The ISR is not allowed to do any time consuming actions. APC routines are used to execute some code asynchronous in the context address space of a particular thread.
Therefore each thread has its own APC queues - one for kernel mode and one for user mode. This will course execution of the APC routines in the right address space. By means of APC routines, one thread can execute code in the address space of another thread - even a thread from another process. A callback method is not executed immediately on the thread from which it is called, but delayed and executed on the thread, which shall receive the result.
Thread switching is also done by means of a DPC routine. All thread synchronization is therefore done at dispatch level IRQL 2 , so no other thread related jobs must take place at this or higher levels. Instead it must post an APC routine, which can do the job.
In practice, interrupt handling is even more complicated than described here - especially on a multi processor system, but these are the basic principles on a bit system with all minor details omitted. On a bit system, the interrupt system is similar, but with some modifications. This is important when working with serial port because you must have a hardware FIFO buffer First In, First Out , which can hold all characters you receive until the DPC routine in the driver has transfered these data to a software buffer in the driver.
As this may easily take mS, the software buffer in the driver should be at least times as big as the hardware buffer.
The interrupt system DPC routine is not allowed to perform very time consuming or thread related operations, so all further processing must be done by non-interrupt routines. There are two ways to do this. Each event can be executed on its own thread. This is usually done by means of a background thread, which waits for one or more events. It can then grap a thread from the thread pool and use this for further processing of the various events so that the background thread immediately gets ready for the next event.
This is the method used in SerialPort. More events can be executed on the same thread. This is the method used by the UI. All UI related actions gets translated to a message. It is possible to post up to 10, messages to one queue. This ensures that a window receives its input messages in the proper first in, first out FIFO sequence. The routine that reads from the message queue is called the message pump. The loop then performs any message translations by means of TranslateMessage.
These virtual-key messages contain a code that identifies which key was pressed or released, but not its character value, which might depend on the state of the Shift or Alt key or the character Language. At last, the message pump calls DispatchMessage, which calls the message handling procedure - WndProc - of the control window specified in the message. Note that in case of one of the four thread safe methods - Invoke, BeginInvoke, EndInvoke and CreateGraphics, it is WhdProc of the control you have used in the call, which will receive the message - for example Button2.
WndProc in case of Button2. BeginInvoke - even though Button2 may have absolutely nothing to do with the message! Message Select Case m. NET 1. 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 messages! Note that both events are raised before the form is closed so that it is possible to cancel the operation instance.
When the associated method like OnClick or OnPaint has done whatever it has to do, it must call any other methods, which shall also be executed when this event occurs. These methods are called event handlers, and the method, which executes the event handlers, is RaiseEvent.
It is a very confusing name because it makes you believe that it raises a new event like raising a flag or an interrupt. It doesn't.
It just execute some event handlers from a list, but it is a convenient way of describing things. You write some event handlers and when you want to execute these, you just "raise the event". The event has a name similar to the message and the associated method except that no prefix is used like for example just Click. When the method and any event handler s have finished their jobs, DispatchMessage returns and the loop calls GetMessage again to wait for the next message.
Let us take an example. If the user moves or resizes a window, some part of the window - a rectangle, a region or maybe the whole window - needs to be redrawn. The method, which has moved or resized the windows, tells which part it is by calling Invalidate.
However, there may be other UI events, which has occured before the window has been changed and also needs to be executed, so the redraw is not done immediately. If you for example has created graphics with CreateGraphics, this graphics may need to be redrawn so you must make a handler for the Paint event, which can do this. The OnPaint method and any other methods associated with a message are overridable so that they may be changed if you derive a class from another.
All applications or services, which use ChildClass, can then subscribe to the Paint event of this class if they have any graphics to redraw in case the window is invalidated. A typical GUI application, after doing some initialization in the Main method, will then start running the message pump. Because the message pump is an infinite loop it will run until the application closes, so the Main thread can't do anything else once the message pump starts. The System. Run method takes care of message pumping.
If no form is specified, it begins running a standard application message loop on the current thread usually the UI-thread for the application or service.
If a form is specified, it also makes the specified form visible like: Shared Sub Main ' Called from the primary thread Application. EnableVisualStyles Application. Run New Form1 ' Start the application and make Form1 visible End Sub In case of an application, a form is usually specified or else there is no UI the user can click, but it is also possible to show the form later by means of NameOfForm. Show if an event to do this is available. If you want to hide a form, you can call NameOfForm. This will set the Visible property to false.
If you want to close a form, you can call NameOfForm. Each application can have many UI-threads, which again can have many windows, but the thread that creates a window must also be the thread that handles all messages send to that window. All the controls in a single window must be created on that windows UI thread, but if you have multiple top-level windows, you can have multiple UI threads - as many as you have windows if you really want.
It has the advantage that if one window is blocked the others may still be functional. All methods and event handlers runs on the same thread as the one from which they are called - either directly, by means of a delegate described later or by means of a raised event, which is actually the same as a delegate call! Because the message pump runs on the UI thread, the methods it calls will do the same, and if these methods raise events as the OnPaint method, the event handlers will also run on the UI thread.
However, if an event handler is activated by means of an event, which for example is raised from a thread pool thread for example in case of SerialPort, then the event handler will also use the thread pool thread and it is therefore not allowed to call methods of the UI thread except for four thread safe methods - Invoke, BeginInvoke, EndInvoke and CreateGraphics described later.
In two cases, it may be desiable to empty the message queue. To keep the UI thread responsible while a big UI job is running. Note that it is not recommended to run big jobs on the UI thread! To ensure that the UI is updated before a thread goes to sleep. In this way, the user will not notice that the UI thread is dead for for example mS. S he sees an immediate responce to the mouse click and before s he can click the mouse again, the UI thread is ready.
During the sleep pause, mouse movements are not blocked as they are not handled by the message queue, but send directly to WndProc. It is possible to empty the message queue by calling System. Note that it is not necessary to specify System. Forms - just Application. DoEvents , and you may get a build error if you imports System.
Forms, which is actually quite un-logical. If you use Application. DoEvents, you should be aware of two problems: There is a very small chance that one of the messages, which get processed, is a message to close down the window.
The routine, which calls Application. DoEvents , must be able to handle this. Maybe there is no longer any window or form when Application. DoEvents returns. You can handle this problem by letting the form close event set a flag, which you can test after Application. There is a small chance that one of the messages is the same message as the one, which gets processed.
This is know as the re-entrance problem. The re-entrance problem can be really nasty and very difficult to handle. In case of a simple message without any data, you can just skip any code in subsequent calls by means of a flag or a lock and "Exit Sub", but there are numerous situations where you need the message so that this is not possible.
You can also disable the control, which sends the message - for example "Button1. For these reasons: Do not use Application. DoEvents unless it is the only resonable way out to solve a problem or flaw in something you cannot change - for example SerialPort or bad drivers.
WParam is used for small pieces of information like flags and LParam is used to points to an object if more information is needed for the message like BulletedListEventArgs and PaintEventArgs. Windows has two basic functions, which are used to post messages - SendMessage and PostMessage. These are Win32 API routines, which you can normally forget all about, but they may be useful in some situations to send messages to controls or forms.
PostMessage just sends the message to the message queue of the target window and returns immediately after. SendMessage blocks the caller till the message gets processed by the message pump.
The subtle but important difference is that messages sent using SendMessage aren't queued in the message queue whereas PostMessage messages are. SendMessage messages are directly "sent" to the message pump.
The message pump retrieves and processes messages sent using SendMessage before looking into those in the message queue. Effectively, there are then two queues, one for SendMessage messages and one for PostMessage messages which is what we call the message queue. The message pump processes all messages in the first queue before starting with the second.
An interesting observation is that if code does a SendMessage from within the message pumping thread, the window procedure WndProc gets called directly, that is, it doesn't go through the message pump. Note that in both cases, the message is executed on the thread that created the window - not on the thread on which PostMessage or SendMessage is called!
SendMessage has a 5 seconds timeout for the target window to process the message. NET, you need another way to do it. Of course standard methods cannot call subroutines and functions, which was unknown when the method was written. You also need another way if you want to change the subroutines and functions to call dynamically while the program is running not fixed at compilation time.
NET has a general usable way to handle this. This is the so-called delegate. A delegate is an object, which has a list called the invocation list, which is able to hold pointers to one or more methods to call Subroutine1, Subroutine2 and Function1 in the above example.
Invoke Data1, Data2 Actually, you don't need to write ". Remember that a delegate may have many methods in its invocation list, which shall be executed with the same data Data1, Data2. In case of only one method in the list, it makes sense to talk about a delegate being executed as the help files do, but it is of course not the delegate, which is executed, but the method s it addresses.
Because such a call can only return one value, only the last method in the invocation list can be a function. However, it may be quite difficult to ensure which method is the last one so in practice all methods should be subroutines if there are more methods than one.
Invoke, BeginInvoke and EndInvoke are described in more details later. In the definition of the delegate it shall be specified whether the last method to call is a function or a subroutine. In case of a subroutine, the delegate is defined as "Public Delegate Sub If we for example want to transfer a string by value to a subroutine, the whole definition becomes: Public Delegate Sub NameOfDelegate ByVal Buffer As String When you define a delegate, the compiler actually creates a complete class definition to support this delegate.
This is used to implement the invocation list. The target object field is only used in case the delegate contains a reference to an instance method like e. In this case, the compiler puts a pointer to Object1 into the target field and a pointer to Method1 into the method field.
If the delegate refers a shared method no object , the compiler sets the target pointer to Null. The two properties Target and Method of the delegate refers to these two fields. AsyncCallback is an optional delegate, which points to a method, which shall be executed when the asynchronous call completes. If the callback method needs any arguments these are transferred in the following object anyObject. IAsyncResult is an interface object, which represents the present state of an asynchronous operation and therefore can be used to monitor the progress of a BeginXXX call like BeginInvoke.
If the method to invoke is a subroutine, the new Invoke and EndInvoke methods are also subroutines. If the method to invoke is a function like in this case, the Invoke and EndInvoke methods are also functions, which returns the return value of the invoked method integer in this case. The reason why the three methods Invoke, BeginInvoke and EndInvoke are build by the compiler and not inherited from the base class multicastDelegate is that the way you call a method shall be the same whether you call it directly or by means of a delegate, and because the number of arguments varies, you cannot use a standard method or would have to combine all arguments in a single object.
BeginInvoke, which is described later, is a very good example of the necessary limitations if the compiler did not tailor cut the three methods to the actual needs. Use of the three methods is described in details below. Delegates are sometimes described as type-safe function pointers because they are similar to function pointers used in other programming languages like C, but unlike function pointers, which can only reference shared methods, that is, subroutines and functions that is called without a specific instance of a class, delegates can also reference instance methods Instance.
As can be seen, the signature is necessary to be able to build the Invoke and BeginInvoke methods how many arguments are needed and of which type.
It is also necessary to be able to decide whether Invoke and EndInvoke shall be subroutines no returned value or functions. Because the Invoke and BeginInvoke methods must be able to call the methods in the invocation list in exactly the same way as a direct call, the delegate must have the same signature number and type of arguments as the method s to call.
Therefore, you cannot use a delegate to point to a method with other arguments than specified in the definition. When you declare a delegate, it is in principle not different from the declaration of normal data types like Bytes, Integers, Arrays and Strings. NET has many standard delegates.
Object, e As System. MethodInvoker increases the efficiency internal in. NET by cutting some corners, so it is recommended to use this delegate if you have no arguments to transfer and does not need information about the sender, which raises the event.
EventHandler is used if you need information about the object that raises the event. The signature in the EventHandler delegate defines a subroutine whose first parameter sender is of type Object and refers to the instance that raises the event, and whose second parameter e is derived from type EventArgs and holds any event data.
If the event does not generate event data, the second parameter is simply an instance of EventArgs. Otherwise, the second parameter is a custom type derived from EventArgs and supplies any fields or properties needed to hold the event data. Note however that control. Invoke and control. Empty - even though you have supplied your own EventArgs, so don't use Eventhandler to marshal any call with arguments to another thread described later!
EventHandler is used a lot in. Object, ByVal e As System. Click End Sub As you can see, it automatically inserts the two arguments of the EventHandler delegate. Usually you have a method, which you want to invoke, and then define a delegate to do this, but this is the other way around.
Your subroutine is going to be invoked with the system delegate EventHandler, which cannot be changed, so your subroutine must have the same arguments or else you will get an error message. Click" indicates that this subroutine will handle the event Click from the sender Button1. It is possible for many subroutines to handle the same event, and it is possible for one subroutine to handle many events provided that they have the same signature.
In this case, the various events are just separated with comma like "Handles Button1. Click, Button2. Button This is the way Button1 is declared by Windows Forms designer in the above example. WithEvents is explained in further details in chapter "Event Keywords". You can usually forget all about this delegate except if you want to put your serial port code in its own class.
End Sub Note that the names of the standard delegates are quite confusing. However, they simply abstract the creation and processing of delegates. Event is just a replacement for "Delegate Sub". The delegate is always defined "Sub" because the invocation list can contain many methods eventhandlers so it is impossible to return one value you never know which method is the last one in the invocation list.
Therefore an event cannot be declared " These methods allow delegates, which point to eventhandlers, to be combined added or removed from the invocation list of the event delegate like this: Private Sub MyEventHandler As you can see, eventhandlers may be added and removed while the program is running.
However, if you add an eventhandler, it is very important that you remember to remove it again if you intend to dispose the object, which raise the event. The reason for this is that the automatic garbage collector of. Net does not remove an object from memory as long as it is referenced by eventhandlers. Handles Me. MyEvent It is possible for a subroutine to handle many events.
In this case, the events are just specified as a comma separated list like this Handles Button1. Click, Button3. You can later use RemoveHandler and AddHandler to remove and add your eventhandler from the invocation list. When an object is declared WithEvents, the get and set methods to reference and build and dispose the object is overrided by two new methods as shown below: Private WithEvents cmd As Button Sub Eventhandler End Sub Sub Eventhandler Click, handler3 End If End Set End Property Note that the original name is changed to a property with a get method, which points to the object.
This courses a slight overhead each time you reference the object, but this is the price to pay for a better program overview and reliability. EventHandler and MouseEventHandler are standard delegates so it is actually delegates handler, handler2 and handler3 , which are added to the invocation list in the AddHandler statements.
The invocation list is a list of delegates, which points to the methods to be executed, but when you use AddHandler yourself, you can forget this. VB does this for you. Note what happens if you set Button to nothing, that is, dispose the object. Privacy policy. This topic describes how to use My. Ports to send strings to the computer's serial ports in Visual Basic. This example sends a string to the COM1 serial port. You may need to use a different serial port on your computer. Use the My.
One of the cool features of Visual Basic. In this tutorial we are going to use Visual Basic. In the first section of our tutorial we will build a simple command line program that would show us how to read and write from the Serial port using Visual Basic. Here we are going to use the SerialPort Class provided by the dot net framework to access the port using vb. The code may look similar to Serial Programming using C tutorial since we are using the same dotnet framework.
All the VB. Creating a Vb. You can also use the opensource Sharpdevelop IDE for running the command line programs. One problem with the latest version of Sharpdevelop IDE 5. If you select the " Empty Project " option instead of the " Console Application " ,the Command line window will not be visible while debugging your Project,.
So stick with the " Console Application " option. You can rename the Module1. A dialog will popup asking you to confirm the action. Press OK. Now your file name under your Solution Explorer as well as the Module name on the Source file will be changed to the one specified by you here SerialCommWrite. Now you can add your code for controlling the serialport under Sub Main and start Programming. Adding Files to Your Project and Compiling.
Instead of typing your own code under the Sub Main you want to add the downloaded source files from github directly under your Project Tree. You can first delete the IDE created Module1.
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