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  程序启动后计时初值为15, 之后可通过串口发来的数据(如"99")来修改下一次计时初值.

#include 
   
    unsigned char code DIG_CODE[10] = {0x3f, 0x06, 0x5b, 0x4f, 0x66, 0x6d, 0x7d, 0x07, 0x7f, 0x6f};//对应数码管显示0~9 char buf[2];int tcount = 0;//记录经过的10ms区间段个数int sec = 15;//倒计时初始值记录int sec2 = 15;//倒计时初始值void T0_INT() interrupt 1 //timer0中断, 每10ms触发一次{	TR0 = 0;//关闭timer0	TH0 = 0xD8;	TL0 = 0xF0;//65536 - 10000 = 55536	if(tcount % 2 == 0)	{		//显示个位数		P2 = 0;// P2 = 0 -> (P24, P23, P22) = (0, 0, 0) -> 右数第一个数字点亮		P0 = DIG_CODE[sec2 % 10];		tcount ++;	}	else if(tcount % 2 == 1)	{		//显示十位数		P2 = 1 << 2;//P2 = 0000 0100 -> (P24, P23, P22) = (0, 0, 1) -> 右数第二个数字点亮		P0 = DIG_CODE[sec2 / 10];		tcount ++;	}	if(tcount == 100) //10ms * 100 = 1000ms = 1s -> 1s时间到	{	 	tcount = 0;		sec2 --;		if(sec2 == -1)		{			sec2 = sec;		}	}	TR0 = 1;//重新开启timer0}int main(){	int i = 0;	TMOD = 0x21;	SCON = 0x50;//设置串行通信格式	TH0 = 0xD8;	TL0 = 0xF0;//65536 - 10000 = 55536	IE = 0x82;//EA + ET0 -> 1000 0010	TH1 = 0xE6;	TL1 = 0xE6;//1200bps under 12MHz	RI = 0;	TR0 = 1;//开启timer0	TR1 = 1;//开启timer1	while(1)	{		if(RI == 1)		{			RI = 0;			buf[i++] = SBUF;//接收串口发来的数据			if(i == 2)			{				i = 0;				sec = (buf[0] - 48) * 10 + (buf[1] - 48);			}		}	}	return 0;}