怎样用51单片机P3.3口外部电平变化做一个4位数码管显示的计数器?要求...答:/*p0口接段选,p1口接位选*/ include"reg51.h"define uchar unsigned char define uint unsigned int uchar qian,bai,shi,ge;uint num=0;uchar tab[10]={0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x6f};//共阴数码管的编码 void ISR(void)//中断服务程序 { num++;qian=num...