从PC机的超级终端接受两个数和一个运算符，通过串口传给嵌入式系统，按操作符计算完两数后，把结果发还给PC机的超级终端，调试该程序，直到运行结果正确为止。（实现多位数的加减乘除）-From the PC-HyperTerminal to accept two numbers and an operator, passed through the serial port embedded systems, according to the calculation operator finished