如何使用API实现串行通讯?

Question

如何使用API实现串行通讯?

Answer 1

在Windows环境下，对于串行通讯的控制是通过中断机制驱动的，由系统自行处理。Windows禁止应用程序直接和硬件打交道，程序员只能使用Windows提供的标准函数通过通讯驱动程序与硬件接口。首先，用CreateFile()函数打开通讯端口，然后通过SetupComm() 函数给通讯的输入输出队列分配一定大小的内存缓冲区，接着通过BuildCommDCB()函数 和SetCommState()等函数对主要通讯参数进行设置。初始化完成后就可以利用ReadFile()函数和 WriteFile() 函数对通讯端口进行读写操作了。程序界面如图所示。本文提供的实例程序使用简单方便。利用一条串行数据线连接在两台计算机Com2之间就可以进行文本文件传输。对于Delphi的具体编程方法这里不再赘述。实例中有详细注释。  unit comunate;
interface
uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,
  Dialogs, Buttons, StdCtrls, ComCtrls;
const
  WM_COMMNOTIFY = WM_USER + 1;  // 通讯消息
type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    Button4: TButton;
    OpenDialog1: TOpenDialog;
Label1: TLabel;
BitBtn1: TBitBtn;
    RichEdit1: TRichEdit;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
    procedure Button4Click(Sender: TObject);
  private
    { Private declarations }
    procedure WMCOMMNOTIFY(var Message :TMessage);message WM_COMMNOTIFY;
  public
    { Public declarations }
  end;
  
var
  Form1: TForm1;
implementation
{$R *.DFM}
var
  hNewCommFile,Post_Event: THandle;
  Read_os : Toverlapped;
  Receive :Boolean;
  ReceiveData : Dword;
  
procedure AddToMemo(Str:PChar;Len:Dword);  // 接收的数据送入显示区
begin
  str[Len]:=#0;
  Form1.RichEdit1.Text:=Form1.RichEdit1.Text+StrPas(str);
end;
 
procedure CommWatch(Ptr:Pointer);stdcall;     // 通讯监视线程
var
  dwEvtMask,dwTranser : Dword;
  Ok : Boolean;
  Os : Toverlapped;
begin
  Receive :=True;
  FillChar(Os,SizeOf(Os),0);
  Os.hEvent :=CreateEvent(nil,True,False,nil); // 创建重叠读事件对象
  if Os.hEvent=null then
    begin
      MessageBox(0,'Os.Event Create Error !','Notice',MB_OK);
      Exit;
    end;
  if (not SetCommMask(hNewCommFile,EV_RXCHAR)) then
    begin
      MessageBox(0,'SetCommMask Error !','Notice',MB_OK);
      Exit;
    end;
  while(Receive) do
    begin
      dwEvtMask:=0;
      // 等待通讯事件发生
      if not WaitCommEvent(hNewCommFile,dwEvtMask,@Os) then
        begin
          if ERROR_IO_PENDING=GetLastError then
             GetOverLappedResult(hNewCommFile,Os,dwTranser,True)
        end;
      if ((dwEvtMask and EV_RXCHAR)=EV_RXCHAR) then
        begin
          // 等待允许传递WM_COMMNOTIFY通讯消息
          WaitForSingleObject(Post_event,INFINITE);
          // 处理WM_COMMNOTIFY消息时不再发送WM_COMMNOTIFY消息
          ResetEvent(Post_Event);
          // 传递WM_COMMNOTIFY通讯消息
          Ok:=PostMessage(Form1.Handle,WM_COMMNOTIFY,hNewCommFile,0);
          if (not Ok) then
            begin
              MessageBox(0,'PostMessage Error !','Notice',MB_OK);
              Exit;
            end;
        end;
    end;
  CloseHandle(Os.hEvent); // 关闭重叠读事件对象
end;
  
procedure TForm1.WMCOMMNOTIFY(var Message :TMessage);  // 消息处理函数
var
  CommState : ComStat;
  dwNumberOfBytesRead : Dword;
  ErrorFlag : Dword;
  InputBuffer : Array [0..1024] of Char;
begin
  if not ClearCommError(hNewCommFile,ErrorFlag,@CommState) then
    begin
      MessageBox(0,'ClearCommError !','Notice',MB_OK);
      PurgeComm(hNewCommFile,Purge_Rxabort or Purge_Rxclear);
      Exit;
    end;
  if (CommState.cbInQue>0) then
    begin
      fillchar(InputBuffer,CommState.cbInQue,#0);
      // 接收通讯数据
      if (not ReadFile( hNewCommFile,InputBuffer,CommState.cbInQue,
                        dwNumberOfBytesRead,@Read_os )) then
        begin
          ErrorFlag := GetLastError();
          if (ErrorFlag <> 0) and (ErrorFlag <> ERROR_IO_PENDING) then
            begin
              MessageBox(0,'ReadFile Error!','Notice',MB_OK);
              Receive :=False;
              CloseHandle(Read_Os.hEvent);
              CloseHandle(Post_Event);
              CloseHandle(hNewCommFile);
             Exit;           end
          else
            begin           
             WaitForSingleObject(hNewCommFile,INFINITE); // 等待操作完成
             GetOverlappedResult(hNewCommFile,Read_os,
                                  dwNumberOfBytesRead,False);
            end;
       end;
      if dwNumberOfBytesRead>0 then
        begin
          Read_Os.Offset :=Read_Os.Offset+dwNumberOfBytesRead;
          ReceiveData := Read_Os.Offset;
          // 处理接收的数据
          AddToMemo(InputBuffer,dwNumberOfBytesRead);
        end;
end;
  // 允许发送下一个WM_COMMNOTIFY消息
  SetEvent(Post_Event);
end;
  
procedure TForm1.Button1Click(Sender: TObject); // 打开文件用于发送
begin
  if OpenDialog1.Execute then
    begin
      Button3.Enabled :=False;
      Button4.Enabled :=False;
      RichEdit1.Lines.LoadFromFile(OpenDialog1.FileName);
      Form1.Caption := IntToStr(RichEdit1.GetTextLen);
    end;
    Button1.Enabled :=False;
end;
  

Answer 2

procedure TForm1.Button2Click(Sender: TObject); // 发送数据
var
  dcb : TDCB;
  Error :Boolean;
  dwNumberOfBytesWritten,dwNumberOfBytesToWrite,
  ErrorFlag,dwWhereToStartWriting : DWORD;
  pDataToWrite : PChar;
  write_os: Toverlapped;
begin
  Form1.Caption :='';
  // 打开通讯端口COM2
  hNewCommFile:=CreateFile( 'COM2',GENERIC_WRITE,0,
                           nil, OPEN_EXISTING,FILE_FLAG_OVERLAPPED,0 );
  if hNewCommFile = INVALID_HANDLE_VALUE then
     MessageBox(0,'Error opening com port!','Notice',MB_OK);
  SetupComm(hNewCommFile,1024,1024); // 设置缓冲区大小及主要通讯参数
  GetCommState( hNewCommFile,dcb);
  dcb.BaudRate :=9600;
  dcb.ByteSize :=8;
  dcb.Parity :=NOPARITY;
  dcb.StopBits := ONESTOPBIT;
  Error := SetCommState( hNewCommFile, dcb );
  if ( not Error) then MessageBox(0,'SetCommState Error!','Notice',MB_OK);
  dwWhereToStartWriting := 0;
  dwNumberOfBytesWritten := 0;
  dwNumberOfBytesToWrite :=RichEdit1.GetTextLen;
  if (dwNumberOfBytesToWrite=0) then
    begin
      ShowMessage('Text Buffer is Empty!');
      Exit;
    end
  else
    begin
      pDataToWrite:=StrAlloc(dwNumberOfBytesToWrite+1);
      try
        RichEdit1.GetTextBuf(pDataToWrite,dwNumberOfBytesToWrite);
        Label1.Font.Color :=clRed;
        FillChar(Write_Os,SizeOf(write_os),0);
        // 为重叠写创建事件对象
        Write_Os.hEvent := CreateEvent(nil,True,False,nil);
        SetCommMask(hNewCommFile,EV_TXEMPTY);
        Label1.Caption:='正在发送数据...!';
        repeat
           Label1.Repaint;
           // 发送通讯数据
           if not WriteFile( hNewCommFile,pDataToWrite[dwWhereToStartWriting],
                              dwNumberOfBytesToWrite,dwNumberOfBytesWritten,
                         @write_os ) then
           begin
               ErrorFlag :=GetLastError;
               if ErrorFlag<>0 then
                 begin
                  if ErrorFlag=ERROR_IO_PENDING then
                     begin
                       WaitForSingleObject(Write_Os.hEvent,INFINITE);
                       GetOverlappedResult(hNewCommFile,Write_os,
                                           dwNumberOfBytesWritten,False);
                     end
                   else
                     begin
                       MessageBox(0,'WriteFile Error!','Notice',MB_OK);
                       Receive :=False;
                       CloseHandle(Read_Os.hEvent);
                       CloseHandle(Post_Event);
                       CloseHandle(hNewCommFile);
                       Exit;
                     end;
                end;
             end;
        Dec( dwNumberOfBytesToWrite, dwNumberOfBytesWritten );
           Inc( dwWhereToStartWriting, dwNumberOfBytesWritten );
        until (dwNumberOfBytesToWrite <= 0);  // Write the whole thing!
        Form1.Caption:=IntToStr(dwWhereToStartWriting);
      finally
        StrDispose(pDataToWrite);
      end;
      CloseHandle(hNewCommFile);
    end;
  Label1.Font.Color :=clBlack;
  Label1.Caption:='发送成功!';
  Button1.Enabled :=True;  Button3.Enabled :=True;  Button4.Enabled :=True;end;
 procedure TForm1.Button3Click(Sender: TObject); // 接收处理var  Ok : Boolean;  dcb : TDCB;  com_thread: Thandle;  ThreadID:DWORD;begin  ReceiveData :=0;  Button1.Enabled :=False;  Button2.Enabled :=False;  RichEdit1.Clear;  // 打开COM2  hNewCommFile:=CreateFile( 'COM2'，GENERIC_READ,0,                         nil, OPEN_EXISTING,FILE_FLAG_OVERLAPPED,0 );  if hNewCommFile = INVALID_HANDLE_VALUE then     begin       MessageBox(0,'Error opening com port!','Notice',MB_OK);       Exit;     end;  Ok:=SetCommMask(hNewCommFile,EV_RXCHAR);  if ( not Ok) then    begin      MessageBox(0,'SetCommMask Error!','Notice',MB_OK);      Exit;    end;  SetupComm(hNewCommFile,1024,1024);  GetCommState( hNewCommFile, dcb );  dcb.BaudRate :=9600;  dcb.ByteSize :=8;  dcb.Parity :=NOPARITY;  dcb.StopBits := ONESTOPBIT;  Ok := SetCommState( hNewCommFile, dcb );  if ( not Ok) then MessageBox(0,'SetCommState Error!','Notice',MB_OK);  FillChar(Read_Os,SizeOf(Read_Os),0);  Read_Os.Offset := 0;  Read_Os.OffsetHigh := 0;  // Create Event for Overlapped Read  Read_Os.hEvent :=CreateEvent(nil,true,False,nil);  if Read_Os.hEvent=null then    begin      CloseHandle(hNewCommFile);      MessageBox(0,'CreateEvent Error!','Notice',MB_OK);      Exit;    end;  // Create Event for PostMessage  Post_Event:=CreateEvent(nil,True,True,nil);  if Post_Event=null then    begin      CloseHandle(hNewCommFile);      CloseHandle(Read_Os.hEvent);      MessageBox(0,'CreateEvent Error!','Notice',MB_OK);      Exit;end;  // 建立通信监视线程  Com_Thread:=CreateThread(nil,0,@CommWatch,nil,0,ThreadID);  if (Com_Thread=0) then    MessageBox(Handle,'No CraeteThread!',nil,mb_OK);  EscapeCommFunction(hNewCommFile,SETDTR);  Label1.Font.Color :=clRed;  Label1.Caption:='正在接收数据...!';end;  procedure TForm1.Button4Click(Sender: TObject); // 停止通讯处理begin  Label1.Font.Color :=clBlack;  Label1.Caption:='infomation';  Form1.Caption := IntToStr(ReceiveData);  Receive :=False;  CloseHandle(Read_Os.hEvent);  CloseHandle(Post_Event);  CloseHandle(hNewCommFile);  Button1.Enabled :=True;  Button2.Enabled :=True;end;
end.

Answer 3

串口通信源程序 
简介：
在MFC下，编写串口通信程序包括两种方法，一种是使用MSComm控件，一种是使用API通信函数。本程序演示了如何使用串口通信API实现串口通信。 
http://www.8860.net/delphicode/dispdoc.asp?id=55