.include "8535def.inc"
 .org $0000
 rjmp reset
 .org $004
 rjmp TIM2_OVF
tab:.db $3f,$06,$5b,$4f,$66,$6d,$7d,$07,$7f,$6f
reset: ldi r16,low(ramend);棧指針置初值
       out spl,r16
       ldi r16,high(ramend)
       out sph,r16
       ldi r16,$ff        ;定義PB、PD為輸出口
       out ddrb,r16
       out ddrd,r16
       ldi r26,0          ;設時、分、秒初值為00：00：00
       ldi r27,0 
       ldi r28,0
       ldi r16,$08        ;使用異步時鐘
       out assr,r16 
       ldi r16,$40        ;允許T2溢出中斷
       out timsk,r16
       ldi r16,$05        ;128分頻，1s中斷一次
       out tccr2,r16
       ldi r16,$00        ;T/C2置初值0
       out tifr,r16
       sei      
aa:    mov r16,r26        ;秒寄存器中數(shù)二轉(zhuǎn)十，送r19、r18
       rcall b8td
       mov r19,r17
       mov r18,r16
       mov r16,r27        ;分寄存器中數(shù)二轉(zhuǎn)十，送r21、r20
       rcall b8td
       mov r21,r17
       mov r20,r16
       mov r16,r28        ;時寄存器中數(shù)二轉(zhuǎn)十，送r25、r22
       rcall b8td
       mov r25,r17
       mov r22,r16
       rcall smiao        ;調(diào)動態(tài)掃描
       rjmp aa
 
TIM2_OVF:
       in r1,sreg         ;保護標志
       inc r26            ;秒增1
       cpi r26,60         ;到60秒？
       brne tt
       clr r26            ;到了，則秒清零
       inc r27            ;分增1
       cpi r27,60         ;到60分？
       brne tt
       clr r27            ;到了，則分清零
       inc r28            ;時增1
       cpi r28,24         ;到24時？
       brne tt
       clr r28            ;到了，則時清零
tt:    out sreg,r1
       reti
    
b8td:  clr r17            ;將r16中的二進制數(shù)轉(zhuǎn)換為十進制數(shù)，十位送r17,個位送r16
b8td1: subi r16,10
       brcs b8td2
       inc r17
       rjmp b8td1
b8td2: subi r16,(-10)
       ret
smiao: ldi r16,$fe         ;送個位位線
       out portd, r16      
       mov r23,r18         ;將個位的BCD碼送R23
       rcall cqb           ;查七段碼，送B口輸出
       rcall t1ms          ;延時1ms
       ldi r16,$fd         ;送十位位線
       out portd, r16       
       mov r23,r19         ;將十位的BCD碼送R23
       rcall cqb           ;查七段碼，送B口輸出
       rcall t1ms          ;延時1ms
       ldi r16,$fb         ;送百位位線
       out portd,r16
       mov r23,r20         ;將百位的BCD碼送R23
       rcall cqb           ;查七段碼，送B口輸出
       rcall t1ms          ;延時1ms  
       ldi r16,$f7         ;送千位位線
       out portd,r16
       mov r23,r21         ;將千位的BCD碼送R23
       rcall cqb           ;查七段碼，送B口輸出
       rcall t1ms          ;延時1ms
       ldi r16,$ef         ;送萬位位線
       out portd,r16
       mov r23,r22         ;將萬位的BCD碼送R23
       rcall cqb           ;查七段碼，送B口輸出
       rcall t1ms          ;延時1ms
       ret 

cqb:   ldi zh,high(tab*2)  ;七段碼的首地址給Z
       ldi zl,low(tab*2)
       add zl,r23          ;首地址+偏移量
       lpm                 ;查表送B口輸出
       out portb,r0               
       ret
t1ms:    ldi r24,71        ;延時1毫秒子程
         push r24
del2:    push r24
del3:    dec r24
         brne del3
         pop r24
         dec r24
         brne del2
         pop r24
         ret