.model small

.stack

.data
message1 db 'count the time.$'
message2 db 0ah,0dh,'Press any key begin.(except space)',0ah,0dh,'$'
message3 db 'Press space stop.',0ah,0dh,'$'
pretime db '00:00$'
time db 0,0,':',0,0,'$'
clean db 8h,8h,8h,8h,8h,'$'
timecarry db 0
count dw 17

.code
main proc far
start:
    mov ax,@data
    mov ds,ax
    lea dx,message1
    mov ah,9
    int 21h
    lea dx,message2
    mov ah,9
    int 21h
    lea dx,message3
    mov ah,9
    int 21h
    lea dx,pretime
    mov ah,9
    int 21h
    mov ah,1
    int 21h
    cmp al,20h
    jz exit
    mov al,1ch
    mov ah,35h
    int 21h
    push es
    push bx
    push ds
    mov dx,offset counttime
    mov ax,seg counttime
    mov ds,ax
    mov al,1ch
    mov ah,25h
    int 21h
    pop ds
    in al,21h
    and al,11111110b
    out 21h,al
    sti
continue:
    mov ah,1
    int 16h
    cmp al,20h
    jnz continue
    pop dx
    pop ds
    mov al,1ch
    mov ah,25h
    int 21h
exit:
    mov ax,4c00h
    int 21h
main endp

counttime proc near
    push ds
    push ax
    push cx
    push dx
    mov ax,@data
    mov ds,ax
    sti
    inc count 
    cmp count,18
    jnz exito   
    call dealcarry
    mov dx,offset clean
    mov ah,9
    int 21h
    mov dx,offset time
    mov ah,9
    int 21h
    call timeback
    mov count,0
exito:
    pop dx
    pop cx
    pop ax
    pop ds
    iret
counttime endp


dealcarry proc near
    inc [time+4]
    mov si,4
    mov bl,0
    mov bh,10
    call mscarry
    mov si,3
    mov bh,6
    mov bl,1
    call smcarry
    mov si,1
    mov bh,10
    mov bl,2
    call mscarry
    mov si,0
    mov bh,6
    mov bl,3
    call smcarry
    mov bl,0
    mov [timecarry],bl
    call timechange
    ret
dealcarry endp

mscarry proc near
    cmp bl,[timecarry]
    jnz exitt
    mov dh,[time+si]
    cmp dh,bh
    jnz exitt
    sub [time+si],bh
    cmp si,0h
    jz exitt
    dec si
    inc [time+si]
    inc [timecarry]
exitt:
    ret
mscarry endp

smcarry proc near
    cmp bl,[timecarry]
    jnz exitth
    mov dh,[time+si]
    cmp dh,bh
    jnz exitth
    sub [time+si],bh
    cmp si,0h
    jz exitth
    sub si,2
    inc [time+si]
    inc [timecarry]
exitth:
    ret
smcarry endp

timechange proc near
    mov ch,30h
    add [time],ch
    add [time+1],ch
    add [time+3],ch
    add [time+4],ch
    ret
timechange endp

timeback proc near
    mov ch,30h
    sub [time],ch
    sub [time+1],ch
    sub [time+3],ch
    sub [time+4],ch
    ret
timeback endp

    end start