关键字：AT89S51,门铃电路

1．实验任务当按下开关SP1，AT89S51单片机产生“叮咚”声从P1.0端口输出到LM386，经过放大之后送入喇叭。2．电路原理图

3．系统板上硬件连线（1．       把“单片机系统”区域中的P1.0端口用导线连接到“音频放大模块”区域中的SPK IN端口上；（2．       在“音频放大模块”区域中的SPK OUT端口上接上一个8欧或者是16欧的喇叭；（3．       把“单片机系统”区域中的P3.7/RD端口用导线连接到“独立式键盘”区域中的SP1端口上；4．程序设计方法（1．       我们用单片机实定时/计数器T0来产生700HZ和500HZ的频率，根据定时/计数器T0，我们取定时250us，因此，700HZ的频率要经过3次250us的定时，而500HZ的频率要经过4次250us的定时。（2．       在设计过程，只有当按下SP1之后，才启动T0开始工作，当T0工作完毕，回到最初状态。（3．       “叮”和“咚”声音各占用0.5秒，因此定时/计数器T0要完成0.5秒的定时，对于以250us为基准定时2000次才可以。6．汇编源程序T5HZ                  EQU 30HT7HZ                  EQU 31HT05SA                EQU 32HT05SB                 EQU 33HFLAG                 BIT 00HSTOP                  BIT 01HSP1                      BIT P3.7                            ORG 00H                            LJMP START                            ORG 0BH                            LJMP INT_T0START:               MOV TMOD,#02H                            MOV TH0,#06H                            MOV TL0,#06H                            SETB ET0                            SETB EANSP:                   JB SP1,NSP                            LCALL DELY10MS                            JB SP1,NSP                            SETB TR0                            MOV T5HZ,#00H                            MOV T7HZ,#00H                            MOV T05SA,#00H                            MOV T05SB,#00H                            CLR FLAG                            CLR STOP                                              JNB STOP,$                            LJMP NSPDELY10MS:       MOV R6,#20D1:                      MOV R7,#248                            DJNZ R7,$                            DJNZ R6,D1                            RETINT_T0:             INC T05SA                            MOV A,T05SA                            CJNE A,#100,NEXT                            MOV T05SA,#00H                            INC T05SB                            MOV A,T05SB                            CJNE A,#20,NEXT                            MOV T05SB,#00H                            JB FLAG,STP                            CPL FLAG                            LJMP NEXTSTP:                    SETB STOP                            CLR TR0                            LJMP DONENEXT:                JB FLAG,S5HZ                            INC T7HZ                            MOV A,T7HZ                            CJNE A,#03H,DONE                            MOV T7HZ,#00H                            CPL P1.0                            LJMP DONES5HZ:                 INC T5HZ                            MOV A,T5HZ                            CJNE A,#04H,DONE                            MOV T5HZ,#00H                            CPL P1.0                            LJMP DONEDONE:                RETI                            END

7．C语言源程序#includeunsigned char t5hz;unsigned char t7hz;unsigned int tcnt;bit stop;bit flag;void main(void){  unsigned char i,j;  TMOD=0x02;  TH0=0x06;  TL0=0x06;  ET0=1;  EA=1;  while(1)    {      if(P3_7==0)        {          for(i=10;i>0;i--)          for(j=248;j>0;j--);          if(P3_7==0)            {              t5hz=0;              t7hz=0;              tcnt=0;              flag=0;              stop=0;              TR0=1;              while(stop==0);            }        }    }}void t0(void) interrupt 1 using 0{  tcnt++;  if(tcnt==2000)    {      tcnt=0;      if(flag==0)        {          flag=~flag;        }        else          {            stop=1;            TR0=0;          }    }  if(flag==0)    {      t7hz++;      if(t7hz==3)        {          t7hz=0;          P1_0=~P1_0;        }    }    else      {        t5hz++;        if(t5hz==4)          {            t5hz=0;            P1_0=~P1_0;          }      }}