汇编打字游戏。出现了一点小bug！该如何解决

Init_game macro op1,op2,op3,op4,op5,op6  
 mov cx,00h  
 mov dh,op1  
 mov dl,op2 
op6:mov ah,02h        ;设置光标位置
 mov bh,00h  
 int 10h 
 push cx 
 mov ah,0ah           ;重复显示相同字符
 mov al,op3           ;要显示的字符
 mov bh,00h           ;页号
 mov cx,01h           ;显示的次数
 int 10h 
 pop cx 
 inc cx 
 inc op4 
 cmp cx,op5 
 jne op6               ;不等则转移
endm 
clear_screen macro op1,op2,op3,op4 ;清屏宏定义  
 mov ah,06h            
 mov al,00h 
 mov bh,07h 
 mov ch,op1 
 mov cl,op2 
 mov dh,op3 
 mov dl,op4 
 int 10h 
 mov ah,02h            ;设置光标位置
 mov bh,00h            ;页号为0
 mov dh,00h            ;行号为0 
 mov dl,00h            ;列号为0
 int 10h 
endm 
menu macro op1,op2,op3 ;菜单显示宏定义  
 mov ah,02h            ;设置光标位置
 mov bh,00h 
 mov dh,op1 
 mov dl,op2 
 int 10h 
 mov ah,09h 
 lea dx,op3            ;显示op3
 int 21h 
endm 

data segment  
ZK db "WELCOME TO PLAY$"  
no db "date:2003/6/24$" 
meg db "press Enter key to continue.......$" 
meg1 db "when a letter is dropping,please hit it!$" 
meg2 db "press space key to pause!$" 
meg3 db "press ESC key to return main interface!$" 
meg4 db "press letter 'E' to exit!$"
meg5 db "press Enter key to return main interface!$" 
speed dw 600d 
letters db "jwmilzoeucgpravskntxhdyqfb"  
 db "iytpkwnxlsvxrmofzhgaebudjq" 
 db "nwimzoexrphysfqtvdcgljukda" 
letters_bak db "jwmilzoeucgpravskntxhdyqfb"  
 db "iytpkwnxlsvxrmofzhgaebudjq"  
 db "nwimzoexrphysfqtvdcgljukda" 
 time db 'you have take time:$'
letter_counter db 0  
life_flag db 78 dup(0) 
position_flag db 78 dup(0)  
present_position db 1 
start_hour db 0
start_min db 0
start_second db 0 
end_hour db 0
end_min db 0
end_second db 0
data ends 
stack segment para stack 'stack' 
 db 64 dup(0) 
stack ends 
code segment 
 main proc far 
 assume cs:code,ds:data,ss:stack 
 start: mov ax,data 
 mov ds,ax 
 mov letter_counter,00h  
 mov present_position,1  
 lea si,position_flag  
 mov ah,00h 
 mov cx,00h 
init_postion_flag:        ;对position_flag依次赋值为00h
 mov [si],ah      
 inc si 
 inc cx 
 cmp cx,78d 
 jne init_postion_flag 
 lea di,letters          
 lea si,letters_bak 
 mov cx,00h 
init_letters:          ;将letters_bak的值赋给letters
 mov ah,[si] 
 mov [di],ah 
 inc si 
 inc di 
 inc cx 
 cmp cx,78d 
 jne init_letters 
 mov ah,00h 
 lea si,life_flag 
 mov cx,00h 
init_life_flag:       ;对life_flag依次赋值为00h
 mov [si],ah 
 inc si 
 inc cx 
 cmp cx,78d 
 jne init_life_flag 
 mov cx,00h  
 mov ah,01h  
 or ch,00010000b 
 int 10h 
clear_screen 00d,00d,24d,79d             ;清屏
 Init_game 00d,00d,0ah,dl,80d,nextsign1          ;循环显示边框       
 Init_game 24d,00d,0ah,dl,80d,nextsign2          
 Init_game 00d,00d,0ah,dh,25d,nextsign3 
 Init_game 00d,79d,0ah,dh,25d,nextsign4 
 menu 05d,15d,ZK                 ;在第5行15列显示ZK
 menu 07h,15d,no                 ;在第7行15列显示no
 menu 09d,15d,meg 
 menu 11d,15d,meg1 
 menu 13d,15d,meg2 
 menu 15d,15d,meg3 
 menu 17d,15d,meg4 
 put: mov ah,02h                 ;设置光标位置 
 mov bh,00h 
 mov dh,22d                      
 mov dl,33d 
 int 10h 
 mov ah,01h                      ;从键盘输入任意字符 
 int 21h 
 cmp al,0dh                                      
 je speed3                       ;是回车转移到speed3
 cmp al,45h                      ;空格转移到exit   
 je exit 
 exit: mov ah,4ch 
 int 21h  
 speed3: mov ax,speed+12 
 mov speed,ax 
 jmp begin 
 ;开始游戏
 begin: clear_screen 01d,01d,23d,78d              ;清屏宏调用  
 clear_screen 01d,01d,23d,78d  
 Init_game 23d,01d,01h,dl,78d,nextsign5    ;此时dl是33d
 
 ;call  start_time               ;;;;;;;;;;;;;调用之后就不能正常显示字母
 mov ah,02h                                ;设置光标位置
 mov bh,00h 
 mov dh,01h 
 mov dl,01h 
 int 10h

 mov cx,00h  
 lea si,letters                  
nextletter:  
 mov ah,02h                     ;显示letters
 mov dl,[si] 
 int 21h 
 inc si 
 inc cx 
 cmp cx,78d 
 je nextcycle 
 jmp nextletter 
from_front:  
 sub present_position,78d  
 jmp gobackto_si 
find_zero: 
 cmp letter_counter,78d  
 je recycle 
 cmp present_position,78d 
 je from_one 
 mov ah,00h 
 nextsi: add present_position,01h 
 inc si 
 cmp [si],ah 
 je gobackto_di 
 cmp present_position,78d 
 je from_one 
 jmp nextsi 
from_one:mov present_position,01h  
 jmp gobackto_si 
 recycle:mov letter_counter,00h 
 mov present_position,01d 
 lea si,position_flag 
 mov cx,00h 
 mov ah,00h 
clearsi: mov [si],ah 
 inc cx 
 cmp cx,78d
 je nextcycle 
 inc si 
 jmp clearsi 
nextcycle:  
 lea di,letters 
 lea si,position_flag 
 add present_position,31d              ;32d.present_position是用来指定当前光标的所在列
 cmp present_position,78 
 ja from_front          ;大于则转移
gobackto_si: 
 add si,word ptr present_position 
 dec si                  ;指定position_flag第32位置
 mov ah,[si]              ;获取position_flag第32位置的值
 cmp ah,01h 
 je find_zero 
gobackto_di: 
 mov ah,01h 
 mov [si],ah 
 add di,word ptr present_position 
 dec di 
 mov dl,present_position          ;设置光标位置在present_position处
 mov ah,02h  
 mov bh,00h  
 mov dh,01h 
 int 10h 
 mov cx,00h 
nextrow: push cx  
 mov cx,00h 
out_cycle:                       ; 延迟 
 push cx 
 mov cx,00h 
in_cycle:                    ;这种延迟有点怪。。。。还是用
 add cx,01h 
 cmp cx,1000 
 jne in_cycle  
 push dx                   
 mov ah,06h                     ;从键盘输入字符。AL=输入字符
 mov dl,0ffh 
 int 21h 
 pop dx 
 jz pass                    ;上面哪个运算会改变标志位.pop?
 cmp al,1bh                     ;如果键入ESC，则返回主菜单 
 je to_start1 
 cmp al," "                         ;如果键入SPACE，则游戏暂停 
 je pause 
 cmp al,[di]                       ;输入字母正确！则字母消失 
 je disappear 
pass: pop cx                 ;显示字母
 inc cx 
 cmp cx,speed 
 je print 
 jmp out_cycle 
pause: push dx                   ;暂停处理 
 mov ah,06h                ;等待输入一个字符
 mov dl,0ffh 
 int 21h 
 pop dx 
 cmp al," " 
 jne pause 
 jmp pass 
 
to_start1:                      ;返回主菜单
 call end_time
 clear_screen 00,00,24,79 
 mov ah,09h
 lea dx,time
 int 21h
 mov ah,02h
 mov dh,10
 mov dl,30
 int 10h
 mov bx,0
 mov bl,end_hour
 sub bl,start_hour
 call take_time
 mov ah,02h
 mov dl,':'
 int 21h
 mov bx,0
 mov bl,end_min
 sub bl,start_min
 call take_time
 mov ah,02h
 mov dl,':'
 int 21h
 mov bx,0
 mov bl,end_second
 sub bl,start_second
 call take_time
 mov ah,02h
 mov dh,11
 mov dl,30
 int 10h
 mov ah,09h
 lea dx,meg5
 int 21h
put1: 
 mov ah,01h
 int 21h
 cmp al,0dh
 jz start
 jmp put1
print:  
 mov ah,0ah                      ;在当前光标位置写空格  
 mov al," " 
 mov bh,00h 
 mov cx,01h 
 int 10h 
 inc dh                            ;列号+1
 mov ah,02h                     ;改变光标位置 
 mov bh,00h 
 int 10h 
 mov ah,0ah                     ;在当前光标位置写字母  
 mov al,[di] 
 mov bh,00h 
 mov cx,01h 
 int 10h 
 pop cx 
 inc cx 
 cmp cx,21d                       ;一个字母下落过程中有21行
 je print_next_letter 
 jmp nextrow                    ;下一行 
disappear:                      ;击中字母后输出空格 
 pop cx 
 pop cx 
 mov ah,0ah 
 mov al," " 
 mov bh,00h 
 mov cx,01h 
 int 10h 
 jmp hit  
print_next_letter:  
 lea si,life_flag 
 add si,word ptr present_position 
 dec si 
 mov ah,0ah 
 mov al," " 
 mov bh,00h 
 mov cx,01h 
 int 10h 
 inc dh  
 
 mov ah,02h 
 mov bh,00h 
 int 10h 
 mov ah,0ah 
 mov al," " 
 mov bh,00h 
 mov cx,01h 
 int 10h 
 mov ah,1 
 mov [si],ah              ;没击中，将lift_flag相应列号的值设为1
 hit: mov ah,02h 
 mov bh,00h 
 mov dh,01h 
 mov dl,present_position 
 int 10h 
 mov al,[di] ; 出现下一个新字母的数法 
 add al,7 
 cmp al,7ah 
 ja convey_letter           ;大于z就转
 mov ah,0ah                       ;在下落位置处产生一个新字母
 mov bh,00h 
 mov cx,01h 
 int 10h 
 mov [di],al 
 add letter_counter,01h 
 jmp nextcycle 
 convey_letter:  
 sub al,7ah 
 add al,61h 
 mov ah,0ah 
 mov bh,00h 
 mov cx,01h 
 int 10h 
 mov [di],al 
 add letter_counter,01h 
 jmp nextcycle  
 clear_screen 01,01,23,78 
 mov ah,02h 
 mov bh,00h 
 mov dh,11d 
 mov dl,20d 
 int 10h 
 inc dh 
 inc dh 
 mov ah,02h 
 mov bh,00h 
 int 10h 
notkey:  
 mov ah,07h 
 int 21h 
 cmp al,0dh 
 je to_start 
 cmp al,1bh 
 je over 
 jmp notkey 
to_start:  
 clear_screen 00,00,24,79 
 jmp start 
over: clear_screen 01,01,23,78  
 mov ah,02h 
 mov bh,00h 
 mov dh,11d 
 mov dl,15h 
 int 10h 
 mov ah,02h 
 mov bh,00h 
 mov dh,13d 
 mov dl,15h 
 int 10h 
 mov ah,07h 
 int 21h 
 mov ah,07h 
 int 21h 
 clear_screen 00,00,24,79  
 mov ax,4c00h 
 int 21h 
main endp 

start_time proc
 push ax
 push bx
 push cx
 push dx
 mov ah,2ch
 int 21h
 mov start_hour,ch
 mov start_min,cl
 mov start_second,dh
 pop dx
 pop cx
 pop bx
 pop ax
 ret
start_time endp

end_time proc
 push ax
 push bx
 push cx
 push dx
 mov ah,2ch
 int 21h
 mov end_hour,ch
 mov end_min,cl
 mov end_second,dh
 pop dx
 pop cx
 pop bx
 pop ax
 ret
end_time endp
 
take_time proc
  mov ax,bx
  mov cx,0
  mov bx,10
  let1:
  mov dx,0
  inc cx
  idiv bx
  push dx
  cmp ax,0
  jnz let1
  let2:
  pop ax
  add ax,0030h
  mov dl,al
  mov ah,2
  int 21h
  loop let2
  ret
take_time endp 

code ends 
end start 

;每次下落后产生一个新字母，下落顺序是每次列号+32，只有小写.通过present_position来控制光标位置