高分请教：为什么串口总是说I/O悬而未决？

Question

function TCustomComm.Write(const Buf; Count: Integer): Integer;
var
  Overlapped: TOverlapped;
  ErrorCode: Integer;
begin
  Lock;
  try
    FillChar(Overlapped, Sizeof(Overlapped), 0);
    Overlapped.hEvent := FEvent.Handle;
if not WriteFile(FHandle, Buf, Count, dWord(Result),
@Overlapped) and (GetLastError <> ERROR_IO_PENDING) then
begin
      ErrorCode := GetLastError;
      RaiseCommError(sWriteError, ErrorCode);
    end;
    if FEvent.WaitFor(FWriteTimeout) <> wrSignaled then
      Result := -1
    else
     begin
       GetOverlappedResult(Handle, Overlapped, dWord(Result), False);
       FEvent.ResetEvent;
     end;
  finally
    Unlock;
  end;
end;function TCustomComm.Read(var Buf; Count: Integer): Integer;
var
  Overlapped: TOverlapped;
  ErrorCode: Integer;
begin
  Lock;
  try
    FillChar(Overlapped, Sizeof(Overlapped), 0);
    Overlapped.hEvent := FEvent.Handle;
    if not ReadFile(FHandle, Buf, Count, dWord(Result),
      @Overlapped) and (GetLastError <> ERROR_IO_PENDING) then
    begin
      ErrorCode := GetLastError;
      RaiseCommError(sReadError, ErrorCode);
    end;
    if FEvent.WaitFor(FReadTimeout) <> wrSignaled then
      Result := -1
    else
     begin
       GetOverlappedResult(Handle, Overlapped, dWord(Result), False);
       FEvent.ResetEvent;
     end;
  finally
    Unlock;
  end;
end;
／／给个参考吧，好好看看吧，Lock为进入临界区。