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;
public byte StopBits;
public byte XonChar;
public byte XoffChar;
public byte ErrorChar;
public byte EofChar;
public byte EvtChar;
public ushort wReserved1;
}对C++比较熟悉网友应该知道，结构体中这种格式的声明，如DWORD fBinary: 1;是以位为单位进行变量设置的，DCB中相关位一共占4个字节，也就是相当于C#中的一个int变量所占的空间。很明显上面的DCB结构会有问题，实际上后面你设置的串口参数，如奇偶校验由于偏移有问题，虽然你设置了，其实都没有设置成功。
其实也不是我说人家的DCB声明错了就错了，在SerialPort类中你就可以找到微软官方自己的DCB声明（需要反编译SerialPort类），声明如下：
[StructLayout(LayoutKind.Sequential)]
public struct DCB
{
public int DCBlength;
public int BaudRate;
public uint Flags;
public ushort wReserved;
public ushort XonLim;
public ushort XoffLim;
public byte ByteSize;
public byte Parity;
public byte StopBits;
public byte XonChar;
public byte XoffChar;
public byte ErrorChar;
public byte EofChar;
public byte EvtChar;
public ushort wReserved1;
}并且专门有一个设置位标志的函数，如下：
internal void SetDcbFlag(int whichFlag, int setting)
{
uint num;
setting = setting << whichFlag;
if ((whichFlag == 4) || (whichFlag == 12))
{
num = 3;
}
else if (whichFlag == 15)
{
num = 0x1ffff;
}
else
{
num = 1;
}
dcb.flags &= ~(num << whichFlag);
dcb.flags |= (uint)setting;
}经过修改能正确运行的API代码如下（注意，由于我是在WinCE平台上运行，所以DLL的路径为"//windows//coredll.dll"，你修改为"kernel32"后即可在PC机使用）：
///<summary>
/// API串口类 叶帆修改 http://blog.csdn.net/yefanqiu
///</summary>
public class CommPort
{
///<summary>
///端口名称(COM1,COM2...COM4...)
///</summary>
public string Port = "COM1:";
///<summary>
///波特率9600
///</summary>
public int BaudRate = 9600;
///<summary>
///数据位4-8
///</summary>
public byte ByteSize = 8; //4-8
///<summary>
///奇偶校验0-4=no,odd,even,mark,space
///</summary>
public byte Parity = 0; //0-4=no,odd,even,mark,space
///<summary>
///停止位
///</summary>
public byte StopBits = 0; //0,1,2 = 1, 1.5, 2
///<summary>
///超时长
///</summary>
public int ReadTimeout = 200;
///<summary>
///串口是否已经打开
///</summary>
public bool Opened = false;
///<summary>
/// COM口句柄
///</summary>
private int hComm = -1;
#region "API相关定义"
private const string DLLPATH = "//windows//coredll.dll"; // "kernel32";
///<summary>
/// WINAPI常量,写标志
///</summary>
private const uint GENERIC_READ = 0x80000000;
///<summary>
/// WINAPI常量,读标志
///</summary>
private const uint GENERIC_WRITE = 0x40000000;
///<summary>
/// WINAPI常量,打开已存在
///</summary>
private const int OPEN_EXISTING = 3;
///<summary>
/// WINAPI常量,无效句柄
///</summary>
private const int INVALID_HANDLE_VALUE = -1;
private const int PURGE_RXABORT = 0x2;
private const int PURGE_RXCLEAR = 0x8;
private const int PURGE_TXABORT = 0x1;
private const int PURGE_TXCLEAR = 0x4;
///<summary>
///设备控制块结构体类型
///</summary>
[StructLayout(LayoutKind.Sequential)]
public struct DCB
{
///<summary>
/// DCB长度
///</summary>
public int DCBlength;
///<summary>
///指定当前波特率
///</summary>
public int BaudRate;
///<summary>
///标志位
///</summary>
public uint flags;
///<summary>
///未使用,必须为0
///</summary>
public ushort wReserved;
///<summary>
///指定在XON字符发送这前接收缓冲区中可允许的最小字节数
///</summary>
public ushort XonLim;
///<summary>
///指定在XOFF字符发送这前接收缓冲区中可允许的最小字节数
///</summary>
public ushort XoffLim;
///<summary>
///指定端口当前使用的数据位
///</summary>
public byte ByteSize;
///<summary>
///指定端口当前使用的奇偶校验方法,可能为:EVENPARITY,MARKPARITY,NOPARITY,ODDPARITY 0-4=no,odd,even,mark,space
///</summary>
public byte Parity;
///<summary>
///指定端口当前使用的停止位数,可能为:ONESTOPBIT,ONE5STOPBITS,TWOSTOPBITS 0,1,2 = 1, 1.5, 2
///</summary>
public byte StopBits;
///<summary>
///指定用于发送和接收字符XON的值 Tx and Rx XON character
///</summary>
public byte XonChar;
///<summary>
///指定用于发送和接收字符XOFF值 Tx and Rx XOFF character
///</summary>
public byte XoffChar;
///<summary>
///本字符用来代替接收到的奇偶校验发生错误时的值
///</summary>
public byte ErrorChar;
///<summary>
///当没有使用二进制模式时,本字符可用来指示数据的结束
///</summary>
public byte EofChar;
///<summary>
///当接收到此字符时,会产生一个事件
///</summary>
public byte EvtChar;
///<summary>
///未使用
///</summary>
public ushort wReserved1;
}
///<summary>
///串口超时时间结构体类型
///</summary>
[StructLayout(LayoutKind.Sequential)]
private struct COMMTIMEOUTS
{
public int ReadIntervalTimeout;
public int ReadTotalTimeoutMultiplier;
public int ReadTotalTimeoutConstant;
public int WriteTotalTimeoutMultiplier;
public int WriteTotalTimeoutConstant;
}
///<summary>
///溢出缓冲区结构体类型
///</summary>
[StructLayout(LayoutKind.Sequential)]
private struct OVERLAPPED
{
public int Internal;
public int InternalHigh;
public int Offset;
public int OffsetHigh;
public int hEvent;
}
///<summary>
///打开串口
///</summary>
///<param name="lpFileName">要打开的串口名称</param>
///<param name="dwDesiredAccess">指定串口的访问方式，一般设置为可读可写方式</param>
///<param name="dwShareMode">指定串口的共享模式，串口不能共享，所以设置为0</param>
///<param name="lpSecurityAttributes">设置串口的安全属性，WIN9X下不支持，应设为NULL</param>
///<param name="dwCreationDisposition">对于串口通信，创建方式只能为OPEN_EXISTING</param>
///<param name="dwFlagsAndAttributes">指定串口属性与标志，设置为FILE_FLAG_OVERLAPPED(重叠I/O操作)，指定串口以异步方式通信</param>
///<param name="hTemplateFile">对于串口通信必须设置为NULL</param>
[DllImport(DLLPATH)]
private static extern int CreateFile(string lpFileName, uint dwDesiredAccess, int dwShareMode,
int lpSecurityAttributes, int dwCreationDisposition, int dwFlagsAndAttributes, int hTemplateFile);
///<summary>
///得到串口状态
///</summary>
///<param name="hFile">通信设备句柄</param>
///<param name="lpDCB">设备控制块DCB</param>
[DllImport(DLLPATH)]
private static extern bool GetCommState(int hFile, ref DCB lpDCB);
///<summary>
///建立串口设备控制块(嵌入版没有)
///</summary>
///<param name="lpDef">设备控制字符串</param>
///<param name="lpDCB">设备控制块</param>
//[DllImport(DLLPATH)]
//private static extern bool BuildCommDCB(string lpDef, ref DCB lpDCB);
///<summary>
///设置串口状态
///</summary>
///<param name="hFile">通信设备句柄</param>
///<param name="lpDCB">设备控制块</param>
[DllImport(DLLPATH)]
private static extern bool SetCommState(int hFile, ref DCB lpDCB);
///<summary>
///读取串口超时时间
///</summary>
///<param name="hFile">通信设备句柄</param>
///<param name="lpCommTimeouts">超时时间</param>
[DllImport(DLLPATH)]
private static extern bool GetCommTimeouts(int hFile, ref COMMTIMEOUTS lpCommTimeouts);
///<summary>
///设置串口超时时间
///</summary>
///<param name="hFile">通信设备句柄</param>
///<param name="lpCommTimeouts">超时时间</param>
[DllImport(DLLPATH)]
private static extern bool SetCommTimeouts(int hFile, ref COMMTIMEOUTS lpCommTimeouts);
///<summary>
///读取串口数据
///</summary>
///<param name="hFile">通信设备句柄</param>
///<param name="lpBuffer">数据缓冲区</param>
///<param name="nNumberOfBytesToRead">多少字节等待读取</param>
///<param name="lpNumberOfBytesRead">读取多少字节</param>
///<param name="lpOverlapped">溢出缓冲区</param>
[DllImport(DLLPATH)]
private static extern bool ReadFile(int hFile, byte[] lpBuffer, int nNumberOfBytesToRead,
ref int lpNumberOfBytesRead, ref OVERLAPPED lpOverlapped);
///<summary>
///写串口数据
///</summary>
///<param name="hFile">通信设备句柄</param>
///<param name="lpBuffer">数据缓冲区</param>
///<param name="nNumberOfBytesToWrite">多少字节等待写入</param>
///<param name="lpNumberOfBytesWritten">已经写入多少字节</param>
///<param name="lpOverlapped">溢出缓冲区</param>
[DllImport(DLLPATH)]
private static extern bool WriteFile(int hFile, byte[] lpBuffer, int nNumberOfBytesToWrite,
ref int lpNumberOfBytesWritten, ref OVERLAPPED lpOverlapped);
[DllImport(DLLPATH, SetLastError = true)]
private static extern bool FlushFileBuffers(int hFile);
[DllImport(DLLPATH, SetLastError = true)]
private static extern bool PurgeComm(int hFile, uint dwFlags);
///<summary>
///关闭串口
///</summary>
///<param name="hObject">通信设备句柄</param>
[DllImport(DLLPATH)]
private static extern bool CloseHandle(int hObject);
///<summary>
///得到串口最后一次返回的错误
///</summary>
[DllImport(DLLPATH)]
private static extern uint GetLastError();
#endregion
///<summary>
///设置DCB标志位
///</summary>
///<param name="whichFlag"></param>
///<param name="setting"></param>
///<param name="dcb"></param>
internal void SetDcbFlag(int whichFlag, int setting, DCB dcb)
{
uint num;
setting = setting << whichFlag;
if ((whichFlag == 4) || (whichFlag == 12))
{
num = 3;
}
else if (whichFlag == 15)
{
num = 0x1ffff;
}
else
{
num = 1;
}
dcb.flags &= ~(num << whichFlag);
dcb.flags |= (uint)setting;
}
///<summary>
///建立与串口的连接
///</summary>
public int Open()
{
DCB dcb = new DCB();
COMMTIMEOUTS ctoCommPort = new COMMTIMEOUTS();
// 打开串口
hComm = CreateFile(Port, GENERIC_READ | GENERIC_WRITE, 0, 0, OPEN_EXISTING, 0, 0);
if (hComm == INVALID_HANDLE_VALUE)
{
return -1;
}
// 设置通信超时时间
GetCommTimeouts(hComm, ref ctoCommPort);
ctoCommPort.ReadTotalTimeoutConstant = ReadTimeout;
ctoCommPort.ReadTotalTimeoutMultiplier = 0;
ctoCommPort.WriteTotalTimeoutMultiplier = 0;
ctoCommPort.WriteTotalTimeoutConstant = 0;
SetCommTimeouts(hComm, ref ctoCommPort);
//设置串口参数
GetCommState(hComm, ref dcb);
dcb.DCBlength = Marshal.SizeOf(dcb);
dcb.BaudRate = BaudRate;
dcb.flags = 0;
dcb.ByteSize = (byte)ByteSize;
dcb.StopBits = StopBits;
dcb.Parity = (byte)Parity;
//------------------------------
SetDcbFlag(0, 1, dcb); //二进制方式
SetDcbFlag(1, (Parity == 0) ? 0 : 1, dcb);
SetDcbFlag(2, 0, dcb); //不用CTS检测发送流控制
SetDcbFlag(3, 0, dcb); //不用DSR检测发送流控制
SetDcbFlag(4, 0, dcb); //禁止DTR流量控制
SetDcbFlag(6, 0, dcb); //对DTR信号线不敏感
SetDcbFlag(9, 1, dcb); //检测接收缓冲区
SetDcbFlag(8, 0, dcb); //不做发送字符控制
SetDcbFlag(10, 0, dcb); //是否用指定字符替换校验错的字符
SetDcbFlag(11, 0, dcb); //保留NULL字符
SetDcbFlag(12, 0, dcb); //允许RTS流量控制
SetDcbFlag(14, 0, dcb); //发送错误后，继续进行下面的读写操作
//--------------------------------
dcb.wReserved = 0; //没有使用，必须为0
dcb.XonLim = 0; //指定在XOFF字符发送之前接收到缓冲区中可允许的最小字节数
dcb.XoffLim = 0; //指定在XOFF字符发送之前缓冲区中可允许的最小可用字节数
dcb.XonChar = 0; //发送和接收的XON字符
dcb.XoffChar = 0; //发送和接收的XOFF字符
dcb.ErrorChar = 0; //代替接收到奇偶校验错误的字符
dcb.EofChar = 0; //用来表示数据的结束
dcb.EvtChar = 0; //事件字符，接收到此字符时，会产生一个事件
dcb.wReserved1 = 0; //没有使用
if (!SetCommState(hComm, ref dcb))
{
return -2;
}
Opened = true;
return 0;
}
///<summary>
///关闭串口,结束通讯
///</summary>
public void Close()
{
if (hComm != INVALID_HANDLE_VALUE)
{
CloseHandle(hComm);
}
}
///<summary>
///读取串口返回的数据
///</summary>
///<param name="NumBytes">数据长度</param>
public int Read(ref byte[] bytData, int NumBytes)
{
if (hComm != INVALID_HANDLE_VALUE)
{
OVERLAPPED ovlCommPort = new OVERLAPPED();
int BytesRead = 0;
ReadFile(hComm, bytData, NumBytes, ref BytesRead, ref ovlCommPort);
return BytesRead;
}
else
{
return -1;
}
}
///<summary>
///向串口写数据
///</summary>
///<param name="WriteBytes">数据数组</param>
public int Write(byte[] WriteBytes, int intSize)
{
if (hComm != INVALID_HANDLE_VALUE)
{
OVERLAPPED ovlCommPort = new OVERLAPPED();
int BytesWritten = 0;
WriteFile(hComm, WriteBytes, intSize, ref BytesWritten, ref ovlCommPort);
return BytesWritten;
}
else
{
return -1;
}
}
///<summary>
///清除接收缓冲区
///</summary>
///<returns></returns>
public void ClearReceiveBuf()
{
if (hComm != INVALID_HANDLE_VALUE)
{
PurgeComm(hComm, PURGE_RXABORT | PURGE_RXCLEAR);
}
}
///<summary>
///清除发送缓冲区
///</summary>
public void ClearSendBuf()
{
if (hComm != INVALID_HANDLE_VALUE)
{
PurgeComm(hComm, PURGE_TXABORT | PURGE_TXCLEAR);
}
}
}后记：我的串口程序修改为API方式后，实际发现与SerialPort类遇到同样的问题，所以SerialPort类还是值得信任的。该API方式的代码在WinCE平台和PC平台都调试通过。
