倒计时演示2.asm

一些单片机汇编程序 流水灯 键盘 lcd A/D D/A等

;利用中断的99秒倒计时器
ORG 00H
JMP START
ORG 0BH
JMP TIM0
START:MOV R3,#00
      MOV R4,#100
      MOV DPTR,#TABLE
      MOV SP,#40H
      MOV TMOD,#01H
      MOV TH0,#HIGH(65536-3800)
      MOV TL0,#LOW(65536-3800)  ;初值4Ms
      SETB TR0
      MOV IE,#82H
TIM0:
     MOV TH0,#HIGH(65536-3800)
     MOV TL0,#LOW(65536-3800)
     INC R3
     CJNE R3,#250,X1
     MOV R3,#00
     DEC R4
     MOV A,R4
     MOV B,#10
     DIV AB
     MOV 20H,B ; 个位
     MOV 21H,A  ; 十位
     CJNE R4,#00,DD1
     MOV R4,#100
 DD1:    CALL SCAN
X1:  PUSH ACC
      PUSH PSW
      CALL SCAN
      POP PSW
      POP ACC
      RETI
SCAN:MOV P2,#11111011B ;扫描子程序
     MOV A,20H
     MOVC A,@A+DPTR
     MOV P0,A
     CALL DELAY1
     MOV P2,#11111101B
     MOV A,21H
     MOVC A,@A+DPTR
     MOV P0,A
     CALL DELAY1
     RET
DELAY:MOV R5,#50
D1:   MOV R6,#40
D2:   MOV R7,#248
      CALL SCAN
      DJNZ R7,$
      DJNZ R6,D2
      DJNZ R5,D1
      RET
DELAY1:MOV R6,#4    ;扫描延时
D3:    MOV R7,#248
       DJNZ R7,$
       DJNZ R6,D3
       RET
TABLE:DB 0C0H,0F9H,0A4H,0B0H,99H,92H,82H,0F8H,80H,90H    ;共阴字码表
END