SerialPort.Open Method

Definition

Namespace:

System.IO.Ports

Assembly:

System.IO.Ports.dll

Package:

System.IO.Ports v9.0.0-rc.2.24473.5

Opens a new serial port connection.

public:
 void Open();

public void Open ();

member this.Open : unit -> unit

Public Sub Open ()

Exceptions

UnauthorizedAccessException

Access is denied to the port.

-or-

The current process, or another process on the system, already has the specified COM port open either by a SerialPort instance or in unmanaged code.

ArgumentOutOfRangeException

One or more of the properties for this instance are invalid. For example, the Parity, DataBits, or Handshake properties are not valid values; the BaudRate is less than or equal to zero; the ReadTimeout or WriteTimeout property is less than zero and is not InfiniteTimeout.

ArgumentException

The port name does not begin with "COM".

-or-

The file type of the port is not supported.

IOException

The port is in an invalid state.

-or-

An attempt to set the state of the underlying port failed. For example, the parameters passed from this SerialPort object were invalid.

InvalidOperationException

The specified port on the current instance of the SerialPort is already open.

Examples

The following code example demonstrates the use of the SerialPort class to allow two users to chat from two separate computers connected by a null modem cable. In this example, the users are prompted for the port settings and a username before chatting. This code example is part of a larger code example provided for the SerialPort class.

public:
    static void Main()
    {
        String^ name;
        String^ message;
        StringComparer^ stringComparer = StringComparer::OrdinalIgnoreCase;
        Thread^ readThread = gcnew Thread(gcnew ThreadStart(PortChat::Read));

        // Create a new SerialPort object with default settings.
        _serialPort = gcnew SerialPort();

        // Allow the user to set the appropriate properties.
        _serialPort->PortName = SetPortName(_serialPort->PortName);
        _serialPort->BaudRate = SetPortBaudRate(_serialPort->BaudRate);
        _serialPort->Parity = SetPortParity(_serialPort->Parity);
        _serialPort->DataBits = SetPortDataBits(_serialPort->DataBits);
        _serialPort->StopBits = SetPortStopBits(_serialPort->StopBits);
        _serialPort->Handshake = SetPortHandshake(_serialPort->Handshake);

        // Set the read/write timeouts
        _serialPort->ReadTimeout = 500;
        _serialPort->WriteTimeout = 500;

        _serialPort->Open();
        _continue = true;
        readThread->Start();

        Console::Write("Name: ");
        name = Console::ReadLine();

        Console::WriteLine("Type QUIT to exit");

        while (_continue)
        {
            message = Console::ReadLine();

            if (stringComparer->Equals("quit", message))
            {
                _continue = false;
            }
            else
            {
                _serialPort->WriteLine(
                    String::Format("<{0}>: {1}", name, message) );
            }
        }

        readThread->Join();
        _serialPort->Close();
    }

    static void Read()
    {
        while (_continue)
        {
            try
            {
                String^ message = _serialPort->ReadLine();
                Console::WriteLine(message);
            }
            catch (TimeoutException ^) { }
        }
    }

public static void Main()
{
    string name;
    string message;
    StringComparer stringComparer = StringComparer.OrdinalIgnoreCase;
    Thread readThread = new Thread(Read);

    // Create a new SerialPort object with default settings.
    _serialPort = new SerialPort();

    // Allow the user to set the appropriate properties.
    _serialPort.PortName = SetPortName(_serialPort.PortName);
    _serialPort.BaudRate = SetPortBaudRate(_serialPort.BaudRate);
    _serialPort.Parity = SetPortParity(_serialPort.Parity);
    _serialPort.DataBits = SetPortDataBits(_serialPort.DataBits);
    _serialPort.StopBits = SetPortStopBits(_serialPort.StopBits);
    _serialPort.Handshake = SetPortHandshake(_serialPort.Handshake);

    // Set the read/write timeouts
    _serialPort.ReadTimeout = 500;
    _serialPort.WriteTimeout = 500;

    _serialPort.Open();
    _continue = true;
    readThread.Start();

    Console.Write("Name: ");
    name = Console.ReadLine();

    Console.WriteLine("Type QUIT to exit");

    while (_continue)
    {
        message = Console.ReadLine();

        if (stringComparer.Equals("quit", message))
        {
            _continue = false;
        }
        else
        {
            _serialPort.WriteLine(
                String.Format("<{0}>: {1}", name, message));
        }
    }

    readThread.Join();
    _serialPort.Close();
}

public static void Read()
{
    while (_continue)
    {
        try
        {
            string message = _serialPort.ReadLine();
            Console.WriteLine(message);
        }
        catch (TimeoutException) { }
    }
}

Public Shared Sub Main()
    Dim name As String
    Dim message As String
    Dim stringComparer__1 As StringComparer = StringComparer.OrdinalIgnoreCase
    Dim readThread As New Thread(AddressOf Read)

    ' Create a new SerialPort object with default settings.
    _serialPort = New SerialPort()

    ' Allow the user to set the appropriate properties.
    _serialPort.PortName = SetPortName(_serialPort.PortName)
    _serialPort.BaudRate = SetPortBaudRate(_serialPort.BaudRate)
    _serialPort.Parity = SetPortParity(_serialPort.Parity)
    _serialPort.DataBits = SetPortDataBits(_serialPort.DataBits)
    _serialPort.StopBits = SetPortStopBits(_serialPort.StopBits)
    _serialPort.Handshake = SetPortHandshake(_serialPort.Handshake)

    ' Set the read/write timeouts
    _serialPort.ReadTimeout = 500
    _serialPort.WriteTimeout = 500

    _serialPort.Open()
    _continue = True
    readThread.Start()

    Console.Write("Name: ")
    name = Console.ReadLine()

    Console.WriteLine("Type QUIT to exit")

    While _continue
        message = Console.ReadLine()

        If stringComparer__1.Equals("quit", message) Then
            _continue = False
        Else
            _serialPort.WriteLine([String].Format("<{0}>: {1}", name, message))
        End If
    End While

    readThread.Join()
    _serialPort.Close()
End Sub

Public Shared Sub Read()
    While _continue
        Try
            Dim message As String = _serialPort.ReadLine()
            Console.WriteLine(message)
        Catch generatedExceptionName As TimeoutException
        End Try
    End While
End Sub

Remarks

Only one open connection can exist per SerialPort object.

The best practice for any application is to wait for some amount of time after calling the Close method before attempting to call the Open method, as the port may not be closed instantly.