单片机按键实现计算器加减乘除；case0x7d:key='F';P1=tab[15];break;///????case0xeb:key='9';a=9;P1=tab[9];break;case0xdb:key='6';a=6;P1=tab[6];break;case0xbb:key='3';a=3;P1=tab[3];break;case0x7b:key='E';res+=(mul*a);P1=tab[res];break;//=cas