find length of string failed.asm

    
    ;find length of string failed  
    
    .model small 
    .stack 100h 
    .data 
    
    str1 db "at harva $"
    
    len db 0
    
    .code 
    
    main proc 
        
        mov ax,@data
        ;initializing data segment 
        
        mov ds,ax
        
        mov si,offset str1
        
        up:
        mov al,[si]
        mov al,'$'
        
        jz dn
        ;if destination =source then zf=1
        
        inc len
        inc si
        loop up
        
        dn:
        ;printing length
        
        mov dl,len 
        add dl,48
        mov ah,2
        int 21h
        
        mov ah,4ch
        ;service routine for exit 
        
        int 21h
        end