convert the case

//convert the case
data segment
string db "HelLo WorLd$"
result db ?
data ends

code segment
assume cs:code,ds:data
start: mov ax,data
       mov ds,ax
       mov cl,00h
       lea si,string
   up: cmp si,'$'
       jz down
       inc si
       jmp up
 down: lea si,string
       lea di,result
  up1: mov al,[si]
       cmp al,60h
       ja lower
       add al,20h
       jmp skip
lower: sub al,20h
  skip: mov [di],al
        inc si
        inc di
        dec cl
        jnz up1
int 03h
code ends
end start