单片机 定时器中断实践,蜂鸣救护车

#include #include sbit SPK = P2^7; unsigned char frq; unsigned int flag; void delayms(unsigned char ms); void main() { TMOD = 0x01; frq = 0x00; TH0 = 0x00; TL0 = 0xff; TR0 = 1; IE = 0x82; flag=0; while(1) { switch(flag) { case 0:frq++;break; //flag标志置0时,frq递增 case 1:frq--;break; //flag标志置1时,frq递减 } if (!(frq^0xff)) flag=1; //当frq增加到FFH时,flag置1,准备frq递减 if (!(frq^0x00)) flag=0; //当frq递减到00H时,flag置0,准备frq递增 delayms(15); } } void timer0() interrupt 1 using 1 { TH0 = 0xfe; TL0 = frq; SPK = ~SPK; } void delayms(unsigned char ms) // 延时子程序 { unsigned char i; while(ms--) { for(i = 0; i < 120; i++); } }