SerialPort.Open Method

Definition

Namespace:

System.IO.Ports

Assembly:

System.IO.Ports.dll

Package:

System.IO.Ports v10.0.0-preview.1.25080.5

Source:

SerialPort.cs

Opens a new serial port connection.

C#

public void 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.

C#

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) { }
    }
}

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.

Applies to