SerialPort Class Help DataReceived

SerialPort Class Help DataReceived

• betolea

  See the thread http://forums.microsoft.com/MSDN/ShowPost.aspx PostID=1379397&SiteID=1 "How does SerialPort handle DataReceived " and especially the answer from nobugz and my last answer.

  
  

• PaulCzy

  I have a similar problem too. I'm developing a bluetooth communication programm between Pocket PC and a bluetooth module on a PC(COM2). I used C# and SerialPort Class to write two programm, one for PC and another for PPC. I can receive data from PC but can not send data from PPC to PC. When I use hyperterminal on PC, the data from PPC can receive. And when i use a USB-Bluetooth Dongle on PC, it also work well. So i think it must be the DataReceived Event not being thrown. But the deep reason i do not clear.
  
  

• aaarrr

  In my application I also don't have a dataReceived event thrown every time when some data is sent from my microcontroller to the pc.
  When the microcontroller is sending only 1 byte, the pc is able to receive it correctly. When the microcontroller is sending a bytestream (i.e. 7 bytes at a time), inaccuracy errors in the reception occur. On the oscilloscoop I do see the transmission of all the bytes, so the problem likely is in the invocation of the event.

  Decreasing the baudrate or increasing the serialport.ReceivedBytesThreshold is no solution.
  

  Reasons for the failure I'm thinking of are the following.
  I'm not using CTS, RTS nor DTR. Does anyone know whether this is the reason for the failure
  Are too many events thrown

  Best regards

  
  
  

• Tom_MTB

  Hi,

  I.m no expert on VB.Net but a man who is wrote a program called serial port chat.

  The receive section explains the use of Delegate to receive data. Apparantly the receive event runs under its own thread and can upset the main thread.

  The article appears on the DEVX.COM website. Type in SerialPortChat to the search page.

  (I cannot get the link to paste here)

  The article is very explicit and clarified the use of SerialPort1 function enough for me to use it as a stand alone VB application to talk to two PCs, then to a PIC micro as well.

  It only handles ascii characters, so binary is a little difficult unless converted to text strings first.

  
  

• J Garcia ARB

  See my previous post.

  DEVX.Com website, SerialPortChat.

  This works fine with ASCII chars, and if I can get it to work, anyone can.

  Regards

  
  

• Eias Nabhan

  I am not sure about why the DataReceived event handler is not being called. Including all of the code that accesses SerialPort1 would help. Some things to keep in mind the DataReceived event handler will not be called if you call Close() on the SerialPort or if you no longer have any references to the SerialPort like after the following method terminates:
  public sub Write
  Dim mySerialPort as new SerialPort("COM1")

  mySerialPort.WriteLine("Hello World")
  mySerialPort.DataReceived = AddressOf MySerialPortDataReceived
  end sub

  The problem with you serialReceive method is that it will not read any data that is received before you call SerialPort1.Open(). So if you do something like the following you will potentially loose data:
  SerialPort1.Open()
  SerialPort1.WriteLine("Hello World")
  SerialPort1.Close()

  serialReceive()

  You should not be opening and closing the SerialPort every time you read or write to it. In general you should open it once and close it once.

  Ryan Byington [MS]
  

  
  
  

• rswipe

  I was not able to repro this problem. I wrote the following repro using a null modem cable between COM1 and COM2 and did not run into the problem that you hit. Is it possible that the device is sending the extra characters

  public class Repro
  {
  static SerialPort com1;

  public static void Main()
  {
  SerialPort com2;

  com1 = new SerialPort("COM1");
  com2 = new SerialPort("COM2");

  com1.Open();
  com2.Open();

  com1.DataReceived += COM1DataReceivedHandler;

  com2.WriteLine("Hello");
  com2.WriteLine("World");
  System.Threading.Thread.Sleep(5000);

  com1.Close();
  com2.Close();
  }

  private static void COM1DataReceivedHandler(Object sender, SerialDataReceivedEventArgs e)
  {
  while(0 < com1.BytesToRead) {
  Console.WriteLine(com1.ReadByte());
  }
  }
  }

  
  
  

• amirmira

  Hi, I'm using the ir as a serial COM, I can transmit data, but i can receive anything.

  The event DataReceived is not generated and the property BytesToRead always is zero.

  Thanks,

  Juan Carlos

  
  

• Manotas

  Without knowing the specifics of your device I can't know for sure but this problem could likely be because the connection settings are incorrect. I would double check the baud rate, data bits, stop bits, and the handshake protocol your device uses.
  
  
  

• TKTOCK

  The state of the CTS, RTS, or DTR pins should not affect the DataReceived event handler. I am not sure if this address your problem but the DataReceived event handler is not guaranteed to get called for every ReceivedBytesThreshold number of bytes received.

  For example if your device sends 3 packets with a length of 7 bytes one right after another and ReceivedBytesThreshold is set to 7 the DataReceived event handler will likely only be called once. In your DataReceived event handler you will have to expect that multiple packets might have been called.

  Ryan Byington [MS]

  
  
  

• d_Sun

  No, it's not the device that is sending the extra characters. It even doesn't matter whether I'm sending the data from a microcontroller or using Hyperterminal.
  
  Doing some small tests make me think that the DataReceivedEvent is only thrown when a next byte is received through the serial port.About your program screenshot: you send via COM2
  char('H') char('e') char('l') char('l') char('o') char(13) char(10) char('W') char('o') char('r') char('l') char('d') char('\r') char(13) char(10)
  right (as the end sequence in Windows is '\r' '\n') Are you sure you receive all of these characters
  
  FYI, here are my serialport properties:
  

  • BaudRate: 57600
  • Databits: 8
  • DiscardNull: false
  • DtrEnable: false
  • GenerateMember: True
  • Handshake: None
  • Modifiers: private
  • Parity: None
  • ParityReplace: 63
  • PortName: COM1
  • ReadBufferSize: 50
  • ReadTimeout:-1
  • ReceivedBytesTreshold: 1
  • RtsEnable: false
  • Stopbits: One
  • WriteBufferSize: 50
  • WriteTimeout: -1

  My best regards,
  
  Koen
  
  
  
  

• PremSamuel

  I agree to you, Ryan, about the ReceivedBytesTreshold. Can you tell me whether using the property this->serialPort1->BytesToRead can help getting al the packets that has been sent

  I noticed that only with the last received byte errors in the DataReceived event occur. I solved this in a not-so-clean way by adding an additional trailerbyte.

  But now another problem happened: when reading a byte from the serialport using the function this->serialPort1->ReadByte() which happens to be character 10 (line feed), automatically a character 13 (carriage return) is added. The problem of adding additional bytes when reading from the serialport is mentioned in msdn, but only when reading form a bytestream and a charstream (which I'm not doing). Changing the property this->serialPort1->Newline to a value different of line feed is no help. Is there a clean way to overcome this problem. Now I solve my problem by checking whether a character 13 follows the character 10.

  An extract of the problem code is below (VC++):

  System::Void serialPort1_DataReceived(System::Object^ sender, System::IO::Ports::SerialDataReceivedEventArgs^ e) {
  DataReceivedCallback^ dr;
  dr = gcnew DataReceivedCallback(this,&casestudy106051117::Form1::replyhandling);

  try{
  while (this->serialPort1->BytesToRead > 0)
  this->Invoke(dr,gcnew cli::array<System::UInt16^>(1){gcnew System::UInt16(this->serialPort1->ReadByte())});
  }catch(InvalidOperationException^ e){e;
  }catch(System::IO::IOException^ e){e;
  }catch(TimeoutException^ e){e;
  }
  delete dr;

  }

  
  
  

• mvarblow

  Have microcontroller and want to send data to PC...

  Anyone has had succes with this

  
  
• SerialPort Class Help DataReceived