SerialPort.Open Method
Definition
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Opens a new serial port connection.
public:
void Open();public void Open ();member this.Open : unit -> unitPublic Sub Open ()Exceptions
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.
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.
The port name does not begin with "COM".
-or-
The file type of the port is not supported.
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.
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.
Applies to
.NET