为什么这个程序的int9键盘中断好象没有执行

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;a15_key.asm
assume cs:code
stack segment
 db 128 dup(0)
stack ends
data segment
  dw 0,0
 data ends
 code segment
 start: mov ax,stack
        mov ss,ax
    mov sp,128
    mov ax,data
    mov ds,ax
    mov ax,0
    mov es,ax
    push es:[9*4]
    pop ds:[0]
    push es:[9*4+2]
    pop ds:[2]
    cli
    mov word ptr es:[9*4],offset int9
    mov es:[9*4+2],cs
        sti
    mov ax,0b800h
    mov es,ax
    mov ah,'a'
s:      mov es:[160*12+40*2],ah
        call delay
    inc ah
    cmp ah,'z'
    jna s
    mov ax,0
    mov es,ax
    cli
    push ds:[0]
    pop es:[9*4]
    push ds:[2]
    pop es:[9*4+2]
    sti
    mov ax,4c00h
    int 21h
delay:  push ax
        push dx
    mov dx,1000h
    mov ax,0
s1:     sub ax,1
        sbb dx,0
    cmp ax,0
    jne s1
    cmp dx,0
    jne s1
    pop dx
    pop ax
    ret
int9:   push ax
        push bx
    push es
    in al,60h
    pushf
    pushf
    pop bx
    and bh,11111100b
    push bx
    popf
    call dword ptr ds:[0] ;
    cmp al,1
    jne int9ret

    mov ax,0b800h
    mov es,ax
    inc byte ptr es:[160*12+40*2+1]
int9ret: pop es
         pop bx
     pop ax
     iret
code ends
end start
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看看这个博文，转自汇编网博客