.model small

.data
        str1 db 'AaOLZzs'
        len equ $ - str1

.code
        mov ax,@data
        mov ds,ax
        LEA SI,str1
        mov cx,7
        L1:
                mov bl,BYTE PTR [SI]
                cmp bl,'Z'
                je encrpZ
                cmp bl,'z'
                je encrpZ1
                add bl,1
                mov [SI],bl
                INC SI
                Loop L1
                jmp ext

        encrpZ:
                mov BYTE PTR [SI],'A'
                INC SI
                Loop L1
                jmp ext

        encrpZ1:
                mov BYTE PTR [SI],'a'
                INC SI
                Loop L1

      ext:
        mov ax,4C00h
        int 21h
end