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Net for Beginners. Serial Port Programming using Visual Basic. Submitted by Rahul. Sreedharan on 25 March - am. Hello folks, Visual Basic. 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.
Imports System 'To Access Console. WriteLine Imports System. GetPortNames Console. Writing into Serial Port Here is a short snippet of code for writing into serial port. Log in to post comments. Comments susheel shinde not verified 11 April - pm Permalink. Ports Imports System. Object, ByVal e As System. EventArgs Handles MyBase. EventArgs Handles btnConnect. EventArgs Handles Button1. EventArgs Handles Button2. EventArgs Handles Button3. InitializeComponent ' Add any initialization after the InitializeComponent call.
If you don't, it is asynchronous. EndInvoke also has the function that it releases the thread to the pool when the job is done. Therefore, delegate. BeginInvoke must always be matched with a delegate.
EndInvoke call the worker must back to the company when the job is done. This is the reason why you cannot call delegate. In case of control. BeginInvoke, it is not necessary with EndInvoke because it uses the UI thread or another thread with a message pump so there is no thread to release job done by a staff worker.
According to the help file in VB. NET, control. BeginInvoke executes a delegate asynchronously on the thread that the control's underlying handle was created on. It is hard to imagine a more cryptically explanation and it is not even true! First of all, a delegate is not something, which is executed. It is just an object pointing to a method. If you know what really happens, it is OK to use the shortcut and just describe it that way, but it is very confusing to a beginner, who may think of a delegate as some kind of subroutine or function since these are the only ones that are executed, and the sub or function keyword in the definition may also lead your thoughts in that direction.
Second, it is not BeginInvoke, which execute the function, but WndProc, which is called from the message pump. This makes a tremendous difference. If it was the BeginInvoke method, the method would be executed immediately and therefore get higher priority than messages already waiting on the message queue, and BeginInvoke would not return before the job was done.
Besides, the method would be executed on the worker thread and would therefore not be able to call methods of controls generated on the UI thread, so nothing would be gained.
Don't feel stupid if you don't understand the help files. How can an intelligent person understand a wrong explanation? All control objects plus the form classes inherit the Invoke and BeginInvoke method from their common base class System. Control as mentioned previously, so they all have this method. You can therefore choose any control object or the form itself Me.
It is usually recommended to use the form Me since it is less confusing than using a control. If you for example use a control and write TextBox1. You don't. You just borrow its BeginInvoke method to invoke another method on the UI thread, which may or may not write to the TextBox.
What you also do with the selected form or control is to use its the so-called ThreadCallbackList if it exists or else it is generated. This list is used to hold a so-called TME ThreadMethodEntry object, which holds all data you want to send to the UI thread including a delegate that points to the method to be executed and an object with the arguments.
The TME object is also used to transfer any returned data and exceptions from the method back to the calling method on the other thread. This is why it is called the ThreadCallbackList. BeginInvoke have only one or two arguments. The first one is a delegate that points to the method s you want to call. The second one is an object, which must hold all arguments to transfer to the method s. As soon as you have made the Invoke or BeginInvoke call, the argument data are copied to the TME object descibed below.
This allows you to reuse the same argument object for new data. If you for example want to send the string "StringToWrite" to the Display routine, which writes to TextBox1, a control.
BeginInvoke statement may look like this: TextBox1. In this case, you don't need to define any delegate, but can just write: TextBox1. These two methods are the typical way control. BeginInvoke and control. Invoke is used in a serial port program like this one. Behind the scenes, control. BeginInvoke are rather complicated and time consuming. If you are a beginner, just skip the rest of this chapter.
When you call Control. BeginInvoke or Control. Invoke the first thing that happens is that the logic looks up the so-called marshaling control by means of the function FindMarshalingControl. The marshaling control is the first control including the current one that has a handle associated with it and therefore can be used in a Windows message see chapter Message Structure.
Usually, the marshaling control will be the one you have used in your BeginInvoke or Invoke statement, but if this control does not have a handle at the time of the BeginInvoke or Invoke call, the logic looks to the parent control, to the parent of the parent, and so on, until it finds a control, which has. If it cannot find any, it still has a way out because all threads, which have a message pump apparently, have a so-called Parking Window, which can be used.
The logic will then use the marshaling control in the actual BeginInvoke or Invoke call, that is, call MarshalingControl. BeginInvoke or MarshalingControl. The only thing these two calls do is to calls the function MarshaledInvoke. The following code shows what this routine does with all minor details like most definitions, internal flags, locks and exception handling omitted.
GetObject control. SetObject control. IsCompleted ' Wait for operation to finish Me. If that control had a handle at the time of the call, the caller will be equal to the marshaling control. Handle " will return the handle of the marshaling control. It will then be this control control. WndProc , which will receive the message from the message pump on the UI thread.
Note that the delegates and the arguments for the method s are not transferred on the message queue. Instead each call of control. Invoke or control. BeginInvoke wraps them into a ThreadMethodEntry object together with the inputdata for the methods and a lot of other information and post this object to the ThreadCallbackList of the marshaling control the list is build if it does not exist.
The message pump will then dispatch the message to WndProc of the marshaling control, which will then execure the delegates in all ThreadMethodEntry objects in its ThreadCallbackList one by one by means of the InvokeMarshaledCallbacks method. Invoke, MarshaledInvoke calls InvokeMarshaledCallBacks directly if the controls are generated on the present thread message queue not used.
Note that InvokeMarshaledCallbacks courses execution of the delegates of all TME objects in the ThreadCallbackList, so the message you post may be executed sooner as you expect if somebody calls control. You need to be aware than any synchronous call can possibly affect your asynchronous calls and cause them to be processed. Also you cannot expect any synchronization between events generated on the UI thread and events generated on other threads.
A delegate method with an invocation list containing the method s to call on the UI thread. One object methodArgs that holds all necessary input arguments for the method s in the invocation list of the delegate. Note that unlike a normal call by means of a delegate, it is only possible with one object, so if more arguments are needed, they must be wrapped in a common argument object.
The reason why the compressed stack is included is that when InvokeMarshaledCallbacks is called on the UI thread, it invokes a delegate that has been initialized on a different thread that may have different permissions. Therefore, the methods on the UI thread are run on the compressed stack copy of call stack so you can't try to Invoke code on the UI thread that you wouldn't have been able to run on your own thread. As can bee seen, TME objects and their execusion on the UI thread involves a huge overhead if you only want to send a "character-received-beep" to the UI thread.
In many ways, Windows are nothing but an object building, object disposing, byte copying machine with very little payload :- Therefore, it is highly recommended to collect a full telegram before you send it to the UI thread.
From a serial port point of view, you can easily call control. BeginInvoke each time your eventhandler for the DataReceived event runs this is done in the sample program because you will just transfer more bytes in case of a heavy load condition, but other Windows programs may suffer from this. In case of BeginInvoke, you may also use a global flag to limit the number of messages on the message queue Invoke is synchronous and will not let you post a new message before the previous one is processed.
Before you call BeginInvoke, you test a flag, which could be Boolean or for example a bit value there is no way a bit value can be half updated due to the pre-emptive multitasking. If the flag is False or the value is Null, you set the flag or value and call BeginInvoke. If the flag is True or the value different from Null, that is, there is already a message of that type on the message queue, you don't call BeginInvoke, but you may update the value.
The method on the UI thread clears the flag False or value Null when it is used. BeginInvoke are programmed in such a way that they are thread safe, that is, able to work on the shared message queue and ThreadCallbackList - even if they are called from more different threads at the same time. This is obtained by means of some locks not shown.
Each byte is transmittet as a start bit logical 0 followed by 7 or 8 data bits with the least significant bit first, any parity bit and a stop bit logical 1 as shown below: Start bit 0 bit 1 bit 2 bit 3 bit 4 bit 5 bit 6 bit 7 Pari. Stop Note that bit 7 and the parity bit are optional. There are two reasons for transmitting the least significant bit first.
The UART is designed to be used with the so-called little-endian or Intel model where all data are right shifted and the least significant byte or word is stored on the lowest address. Because of the right shifting, it is bit 0 the least significant bit , which has a fixed position, no matter if the data is a byte bit , a word bit or a long word. Therefore, it is most practical to transmit this bit first because depending on the telegram length the last bit may be bit 7, bit 15, bit 63 or anything else.
If you ignore the start bit and the stop bit and transmits all bits from one address and up, the stream of bits will start with the least significant bit of the least significant byte and end with the most significant bit of the most significant byte. In systems, which use the big-endian or Motorola model, all data are left shifted, so that the most significant bit of a byte has the same position as the most significant bit of a word or long word. Therefore, it ought to be the most significant bit, which is called bit 0, but most big-endian systems except for the PowerPC are not so consistent.
With the big-endian model, the most significant byte is stored on the lowest address and it is natural to transmit the most significant bit first.
It is most practical with a variable number of data bits 5, 6, 7 or 8 and parity. The standard UART in the PC 16C has a 16 byte transmitter FIFO and a 16 x bit receiver FIFO, which not only contains the received byte, but also three flags, which indicate a break condition, that is, a condition where all bits including the stop bit are logical 0, a framing error, which indicates that the received stop bit is not logical 1 except for break and a parity error, which indicates an error on the odd or even parity.
Advanced UART's are also able to use the parity bit as a 9th bit to distinguish between address and data and very advanced UART's like 16C are able to perform the address comparison automatically, which is very useful on multidrop lines. They even have a 9-bit wide transmitter FIFO to be able to transmit the 9th bit automatically. As described previously, the interrupt latency of Windows is approximately 1 mS so with a 16 x bit receiver FIFO it is able to receive up to At this speed, it takes 1.
If higher transmission speeds are needed, it is necessary to use more advanced UART's. At for example The PC uses voltage levels according to the RS standard to transmit the data. The default line state is logical 1 passive so unfortunately it is not possible to use the Break detection to determine if a unit is connected. It is very important to notice that SerialPort uses "True" as the active state so that true corresponds to logical 0 and not logical 1 as you would expect!
The input impedance of a RS receiver is approximately 5 Kohm. The trig level is not 0V, but approximately 1. This is very useful, because it enables you to connect a modem signal input directly to a logic signal and utilize the event see next chapter. Note however that on old RS receivers, which has a 5 KOhm serial resistor instead of a 5 KOhm pull down resistor modern receivers , the switching times - especially the turn off time - may be increased considerably due to the reduced input current.
A standard 9-pin serial connector contains the following signals pins. The signals may be set or read with the specified properties: CD Carrier Detect. Input, which may be read with the CDHolding property. RXD Receiver Data. Steady state may be read with BreakState. TXD Transmitter Data. Steady state may be set with BreakState. Output, which may be set or read with DtrEnable. SGND Signal ground. Common return signal. Input, wich may be read with DsrHolding.
Output, which may be set or read with RtsEnable. RI Ring Indicator. Input, which cannot be read with SerialPort. Note however that the drive power is very limited. The output pins are usually not able to sink or source more than approximately mA and in some cases even lower. At 12 V, a standard RS input will only draw 2.
If the connected device uses these signals, it will not transmit before the signals are set! The methods used to set these signals use multithreading and therefore do not course the outputs to change immediately! This means that if the time between such statements are less than approximately 11 mS on a single processor system or 16 mS on a multiprocessor system, you cannot expect the time delay to be active.
If you for example write: COMPort. BreakState statements are executed immediately after each other, so that the break transmission does not work! Before a serial port can be opened, a new instance of the System. SerialPort WithEvents means that the new instance is able to raise events like DataReceived when new data are available and PinChanged when any of the moden input signals change state.
If you are only going to use SerialPort for a polled system, you may not need any events and may therefore omit WithEvents. Therefore, it is necessary to close one COM port before opening a new one.
Note that it is necessary with a short time delay to allow the background thread to close down before you are allowed to reopen the port. The new serial port is opened with NameOfSerialPort. The default size for the transmitter buffers is bytes and the default size of the receive buffer is bytes and.
NET ignores any values smaller than these values. The receive buffer should be able to hold all data until the routine, which emties the buffer, gets up and running. If a 16C UART is used, it is therefore necessary to increase the buffer size to for example bytes. It should be noted that many drivers do not support more than 32 kbytes. After the buffer sizes are set, you start to use these buffer.
Therefore the sizes cannot be changed while the port is open. The SerialPort object has yet another buffer on top of the driver buffer. This buffer is only used when using methods dealing with encodings i.
Chars and Strings, but not bytes. When reading bytes, some bytes may be taken out of the buffer, but not put into it, so if you work only with bytes, the internal SerialPort buffer is newer used.
The size of the buffer is bytes. If you are calling a byte-related method like ReadByte or Read byteArray, Offset, Count , the byte is returned directly or the bytes are put directly into your byte array as they arrives. If you are calling an encoding-related method such as ReadChar, ReadLine or ReadTo, then the bytes are first put into the internal buffer and then the char-encoded data are put into your buffer or returned as string, etc, depending on the method.
Remember that. NET uses bit Unicode for all strings and char's so each received byte is converted to a bit value! The data from the driver buffer are not transferred to the SerialPort buffer before you call the encoding-related method. If you are receiving bit Unicode characters and only one byte is received, then it is assumed that the next incomming byte will complete the character, so the first part is buffered.
No half-characters are returned. ReadExisting is a special case because it creates a new buffer with a size equal to the number of bytes available. All data are read out and returned as a string. By default, strings and char's are transmitted not coded as 7-bit ASCII where all characters above are illegal and will be replaced with "?
Therefore, you cannot use a string or char related method to send or read binary information unless you change the encoding to something, which include all values up to like: YourSerialPort. GetEncoding ' or YourSerialPort. If you need to transfer binary values, it is better to use a byte related receive method like ReadByte and use the only byte related send method there is - Write ByteArray, offset, count.
Unfortunately, the width of all buffers is only 8 bits so the synchronization between data, break and error conditions from the receiver FIFO in the UART is lost. It is therefore impossible to separate binary telegrams by means of a break condition or use modern 9th bit communication :- It is important to notice, that the flow control you select in SerialPort is based on software and not always communicated to the driver.
If the driver recognizes the setting of SerialPort, it is then necessary to select "RequestToSend" in SerialPort to avoid that the original driver setting hardware flow control is changed. However, in that case you actually get an undesirable double flow control - one in hardware and one in software. If the driver does not recognize the setting, it is therefore better to set the flow control of SerialPort to "None" so that you only have the hardware control left. After setting the buffer sizes, SerialPort fires up a background thread, which waits for something interesting to happen on the serial port by means of the API function WaitCommEvent.
A character was received and placed in the input buffer. Bit 1. The event character was received and placed in the input buffer. Bit 2. The last character in the output buffer was sent. Bit 3. The CTS clear-to-send signal changed state. Bit 4. The DSR data-set-ready signal changed state. Bit 5. Bit 6. A break was detected on input. Bit 7. A line-status error occurred. Bit 8. A ring indicator was detected. Therefore, it is very difficult to control the modem signals and terminate a telegram with a break condition :- In case of a DataReceived, ErrorReceived or PinChanged event, the background thread calls the API function QueueUserWorkItem , which graps a thread from the thread pool for any further processing of that event.
If no thread is available in the pool, the event is put in queue for a thread therefore Queue The background thread then immediately calls WaitCommEvent again to wait for the next interesting event. WaitCommEvents clears the event flags before it returns of course it doesn't clear the return value , so when WaitCommEvents is called again, the new call will not return before the UART driver has set one or more of the event flags again. The new thread from the thread pool does the following: First it waits to get a lock on the underlying SerialStream object of SerialPort Monitor.
Enter serialStreamObject. The primary reason for this was to coordinate events with closing the serial port so that no events would be raised while closing was in progress, but the lock also ensures that DataReceived, PinChanged or ErrorReceived will not fire again before the event handler returns.
This ensures that there will only be one instance of the event handler and it simplifies programming. Note that there is a mutual blocking between all events so that if for example a thread for DataReceived is running, PinChanged and ErrorReceived are also blocked until the thread is returned to the pool.
In these two cases, it calls your event handler for the DataReceived event. Because it is called from this thread pool thread, the event handler will also use this thread.
The event handler is therefore not allowed to call methods of a control on the UI thread except for the four thread safe methods Invoke, BeginInvoke, EndInvoke and CreateGraphics and hiden methods to set simple properties like the background color.
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