проблемы с перехватом Int 5h

data segment
cur_attr db 14
OLD_CS  dw  ?  
OLD_IP  dw  ?  
data ends
code segment
assume cs:code,ds:data
NEW_5h proc far
push es
push ax
push bx
mov cx,290
mov ax, 0B800h 
mov es, ax 
xor ax,ax
xor bx,bx
inc bx
add cur_attr,1
cmp cur_attr,16
jne cycle3
mov cur_attr,0
cycle3:
mov ah, cur_attr   
mov byte ptr es:[bx], ah       
inc bx
inc bx
loop cycle3
pop bx
pop ax
pop es
iret
NEW_5h endp
CLS     proc        near
push    cx 
push    ax 
push    si 
xor si, si 
mov ah, 7  
mov cx, 2000
CL1:    mov es:[si], ax
inc si     
inc si     
loop    CL1
pop si     
pop ax     
pop cx     
ret
CLS endp   
begin:
mov ax,data
mov ds,ax  
mov ah, 35h    
mov al, 5h
int 21h
mov OLD_IP, bx
mov OLD_CS, es
mov ah, 25h
mov al, 5h
push ds
mov dx, offset NEW_5h
mov bx,seg New_5h
mov ds, bx
int 21h        
pop ds     
mov ax, 0B800h 
mov es, ax     
call    CLS
xor si,si
xor bx,bx
mov cx,290
cycle1:mov al,ds:[si+40]   
mov ah, 14 
mov es:[bx], ax    
inc bx
inc bx
inc si
loop cycle1
mov ax,data
mov ds,ax
mov es,ax
mov ax, 40h    
mov es, ax     
cycle2:mov  ax, es:[1ch]   
mov bx, es:[1ah]   
cmp bx , ax        
jz cycle2
ext:push ds
xor ax,ax
mov ah,25h
mov al, 5h
mov dx,OLD_IP
mov bx,OLD_CS
mov ds, bx
int 21h        
pop ds 
xor ax,ax
mov ax, 4c00h  
int 21h
code ends
end begin