C / C++ / MFC

// Golbal variables
unsigned char ParamBuffer[0x5c];
unsigned char SendBuffer[1024];
unsigned char RecvBuffer[1024];
CWaitDlg      *g_ProgressDlg;

int InitParams()
{
    // Initial the buffer before to write to the serialport.
    // On the side,or read the buffer from some files.
}

int SetSendBuffer(unsigned char *temp,int nLen)
{
    memcpy(ParamBuffer,temp,nLen);
    return 0;
}
int ShowDlg()
{
    // Show the mode progress windows ,and how many buffer was written.
}

int CreateDownThread()
{
    // Here is used a new thread to write the buffer to the serialport.
    ...
}

// this is all global variable 
typedef BOOL (CALLBACK *MyTxtFormat)(char *,char *);	        // this function int other dll
typedef int (CALLBACK *MyShowLoadingDlg)(BOOL);
typedef int (CALLBACK *MySetSendBuffer)(unsigned char *,int nLen);
typedef int  (CALLBACK *MyCreateDownThread)();
typedef int (CALLBACK *MyInitialParam)();

static MyInitialParam		InitialParam;
static MyShowLoadingDlg		ShowLoadingDlg;						
static MySetSendBuffer		SetSendBuffer;
static MyCreateDownThread	CreateDownThread;

HINSTANCE			hCode;
HINSTANCE			hHardware;
MyTxtFormat			TxtFormat;

void CMainFrame::OnDownload()
{
	TCHAR	*szpBuffer = new TCHAR [8000];
	unsigned char szTemp[4096];

	BOOL		bRet = FALSE;
	CFile		pFile;
	DWORD		nActual = 0;

	memset(szpBuffer,255,8000);
	hCode=LoadLibrary("aaa.dll");
	TxtAAA=(MyTxtFormat)GetProcAddress(hCode,"TxtFormat");
	if (TxtToCode)
	{
		bRet = TxtFormat(strLDPath.GetBuffer(strLDPath.GetLength()),
			strBinPath.GetBuffer(strBinPath.GetLength()));
		if(!bRet)
		{
			MessageBox("TxtFormat error！");
			return;
		}
        
		// In the debug window,the szpBuffer is normal.
		if ( pFile.Open( _T(strBinPath),CFile::modeReadWrite | CFile::typeBinary, NULL ) )
		{
			nActual = pFile.Read(szpBuffer, 8000);
		}
	}
    
	// This is my dll,I used F10 to debug step info, that
	hHardware = LoadLibrary("bbb.dll");
	if(hHardware)
	{
		ShowLoadingDlg=(MyShowLoadingDlg)GetProcAddress(hHardware,"ShowLoadingDlg");
		if(ShowLoadingDlg == NULL)
		{
			MessageBox("ShowLoadingDlg Functioin Failed ！");
			return;
		}
		InitialParam = (MyInitialParam)GetProcAddress(hHardware,"InitialParam");
		if(InitialParam == NULL)
		{
			MessageBox("InitialParam Functioin Failed ！");
			return;
		}
		SetSendBuffer=(MySetSendBuffer)GetProcAddress(hHardware,"SetSendBuffer");
		if(SetPlcRam == NULL)
		{
			MessageBox("SetSendBuffer Functioin Failed ！");
			return;
		}
		CreateDownThread = (MyCreateDownThread)GetProcAddress(hHardware,"CreateDownThread");
		if(CreateDownThread == NULL)
		{
			MessageBox("CreateDownThread Functioin Failed ！");
			return;
		}
        
        // Here is to show the progress window.
	ShowLoadingDlg();
        InitialParam();
        SetSendBuffer(pBuffer,sizeof(pBuffer));
        CreateDownThread();
	}

	// This function is overed,but the GUI is all the same hang-up.
	pFile.Close();
	szpBuffer = NULL;
	delete szpBuffer;
	FreeLibrary(hHardware);
}