C# API串口通信问题修复与DCB结构优化

在调试ICU通信设备的时候，由于串口通信老出现故障，所以就怀疑CF实现的SerialPort类是否有问题，所以最后决定用纯API函数实现串口读写。
先从网上搜索相关代码（关键字：C# API 串口），发现网上相关的资料大约来源于一个版本，那就是所谓的msdn提供的样例代码（msdn的具体出处，我没有考证），其它的代码大都是它的变种。
其实这个示例代码是有问题的，也就是说DCB结构体声明的有问题，虽然该代码可以正常通信，不过如果你设置了奇偶校验的话，你会发现奇偶校验无效。
VC中的DCB结构声明如下：
typedef struct _DCB {
    DWORD DCBlength;      /* sizeof(DCB)                     */
    DWORD BaudRate;       /* Baudrate at which running       */
    DWORD fBinary: 1;     /* Binary Mode (skip EOF check)    */
    DWORD fParity: 1;     /* Enable parity checking          */
    DWORD fOutxCtsFlow:1; /* CTS handshaking on output       */
    DWORD fOutxDsrFlow:1; /* DSR handshaking on output       */
    DWORD fDtrControl:2; /* DTR Flow control                */
    DWORD fDsrSensitivity:1; /* DSR Sensitivity              */
    DWORD fTXContinueOnXoff: 1; /* Continue TX when Xoff sent */
    DWORD fOutX: 1;       /* Enable output X-ON/X-OFF        */
    DWORD fInX: 1;        /* Enable input X-ON/X-OFF         */
    DWORD fErrorChar: 1; /* Enable Err Replacement          */
    DWORD fNull: 1;       /* Enable Null stripping           */
    DWORD fRtsControl:2; /* Rts Flow control                */
    DWORD fAbortOnError:1; /* Abort all reads and writes on Error */
    DWORD fDummy2:17;     /* Reserved                        */
    WORD wReserved;       /* Not currently used              */
    WORD XonLim;          /* Transmit X-ON threshold         */
    WORD XoffLim;         /* Transmit X-OFF threshold        */
    BYTE ByteSize;        /* Number of bits/byte, 4-8        */
    BYTE Parity;          /* 0-4=None,Odd,Even,Mark,Space    */
    BYTE StopBits;        /* 0,1,2 = 1, 1.5, 2               */
    char XonChar;         /* Tx and Rx X-ON character        */
    char XoffChar;        /* Tx and Rx X-OFF character       */
    char ErrorChar;       /* Error replacement char          */

    char EofChar;         /* End of Input character          */
    char EvtChar;         /* Received Event character        */
    WORD wReserved1;      /* Fill for now.                   */
} DCB, *LPDCB;
有问题的代码DCB结构声明如下：
[StructLayout(LayoutKind.Sequential)]
        public struct DCB
        {
            public int DCBlength;
            public int BaudRate;
            public int fBinary;
            public int fParity;
            public int fOutxCtsFlow;
            public int fOutxDsrFlow;
            public int fDtrControl;
            public int fDsrSensitivity;
            public int fTXContinueOnXoff;
            public int fOutX;
            public int fInX;
            public int fErrorChar;
            public int fNull;
            public int fRtsControl;
            public int fAbortOnError;
            public int fDummy2;
            public uint flags;
            public ushort wReserved;
            public ushort XonLim;
            public ushort XoffLim;
            public byte ByteSize;
            public byte Parity;