The extension of the microprocessor memory , the keyboard and display adopt typical circuits . because this system have to expend a lot of memory , i / o are used masterly in order to satisfy the design demand 单片机系统外围的的存储器扩展、键盘和显示等部分以选取经典电路为主要设计思路,但本系统要扩展海量存储器,所以巧妙的使用和分配了i o口,以满足设计要求。