;蜂鳴器之報警聲
;P1.0接蜂鳴器,變頻輸出報警

      CODE_SEG SEGMENT CODE 
      DATA_SEG SEGMENT DATA
      STACK_SEG SEGMENT IDATA

      SPK BIT P1.0  ;定義P1.0為蜂鳴器

      RSEG DATA_SEG
  FRQ:DS 1  ;定義1個程序存儲器空間為FRQ
  TMP:DS 1  ;定義1個程序存儲器空間為TMP
      RSEG STACK_SEG

STACK:DS 20  ;定義20個程序存儲器空間，起始地址為STACK

      CSEG AT 00000H  ;程序起始地址
      LJMP MAIN  ;跳轉(zhuǎn)至MAIN
      CSEG AT 0000BH  ;定時/計數(shù)器T0中斷服務(wù)子程序入口地址
      LJMP TIMER0  ;跳轉(zhuǎn)至定時/計數(shù)器T0中斷服務(wù)子程序
      RSEG CODE_SEG

 MAIN:MOV SP,#(STACK-1)  ;堆棧棧頂?shù)刂?      MOV TMOD,#01H  ;定時/計數(shù)器T0采用定時器方式1,16位計數(shù)器
      CLR A  ;A清零
      MOV FRQ,A  ;FRQ清零
      MOV TH0,A  ;計數(shù)初值為0FFH，即65.281ms
      MOV TL0,#0FFH
      SETB TR0  ;啟動T0
      MOV IE,#082H  ;CPU開總中斷，T0開溢出中斷
	
MAIN_LP:INC FRQ  ;FRQ加1
	MOV R7,#04  ;R7=4
	LCALL DELAYMS  ;調(diào)用延時子程序
	SJMP MAIN_LP

TIMER0:MOV TH0,#0FEH  ;重新初始化T0
       MOV TL0,FRQ
       CPL SPK
 RETI 	

;延時子程序
  DELAYMS:MOV A,R7
          JZ END_DLYMS	
  DLY_LP1:MOV R6,#185
  DLY_LP2:NOP
	  NOP
	  NOP
	  DJNZ R6,DLY_LP2
	  DJNZ R7,DLY_LP1
END_DLYMS:RET 

END