MdiChild子窗体中如何调用 Mdi主窗体中的 AdoConnection

MdiChild 封装在Dll中,子窗体中有AdoQuery控件,
Dll 工程文件中的函数为:

function ShowChild(App:TApplication;PFormFreeCallBack:Pointer):TForm;stdcall; export;
begin
Application:=App;
Result:=TDll_Frm.Create(Application);
@FormFreeCallBack:=PFormFreeCallBack;
end;

主窗体的调用为:
ChildForm:=ShowChild(Application,@FormFreeCallBack);

怎样在子窗体中可以调用主窗体中的AdoConnection?

如:
function ShowChild(App:TApplication;PFormFreeCallBack:Pointer;ado:TadoConnection):TForm;stdcall; export;
begin
Application:=App;
Result:=TDll_Frm.Create(Application);
@FormFreeCallBack:=PFormFreeCallBack;
end;

ChildForm:=ShowChild(Application,@FormFreeCallBack,AdoConnection1);

但结果不行.