C#

[StructLayout(LayoutKind.Sequential)]
public struct DCB {
//taken from c struct in platform sdk
public int DCBlength; // sizeof(DCB)
public int BaudRate; // current baud rate
/* these are the c struct bit fields, bit twiddle flag to set
public int fBinary; // binary mode, no EOF check
public int fParity; // enable parity checking
public int fOutxCtsFlow; // CTS output flow control
public int fOutxDsrFlow; // DSR output flow control
public int fDtrControl; // DTR flow control type
public int fDsrSensitivity; // DSR sensitivity
public int fTXContinueOnXoff; // XOFF continues Tx
public int fOutX; // XON/XOFF out flow control
public int fInX; // XON/XOFF in flow control
public int fErrorChar; // enable error replacement
public int fNull; // enable null stripping
public int fRtsControl; // RTS flow control
public int fAbortOnError; // abort on error
public int fDummy2; // reserved
*/
public uint flags;
public ushort wReserved; // not currently used
public ushort XonLim; // transmit XON threshold
public ushort XoffLim; // transmit XOFF threshold
public byte ByteSize; // number of bits/byte, 4-8
public byte Parity; // 0-4=no,odd,even,mark,space
public byte StopBits; // 0,1,2 = 1, 1.5, 2
public char XonChar; // Tx and Rx XON character
public char XoffChar; // Tx and Rx XOFF character
public char ErrorChar; // error replacement character
public char EofChar; // end of input character
public char EvtChar; // received event character
public ushort wReserved1; // reserved; do not use
}

COMMTIMEOUTS *timeouts = new COMMTIMEOUTS ;
memset(timeouts, 0, sizeof(COMMTIMEOUTS)) ;
timeouts->ReadIntervalTimeout          = ReadIntervalTimeout ;
timeouts->ReadTotalTimeoutMultiplier   = 5 ;
timeouts->ReadTotalTimeoutConstant     = readTimeOut ; //...
timeouts->WriteTotalTimeoutConstant    = 0 ; //
timeouts->WriteTotalTimeoutMultiplier  = 2*BaudRate/8 ;
const bool ret = SetCommTimeouts(*hDev, timeouts) != FALSE ;
delete timeouts ;
m_currentTimeOut = readTimeOut ;

_serialPort.ReadTimeout = 500;
_serialPort.WriteTimeout = 500;