IDEAL
MODEL small
STACK 100h
DATASEG
; --------------------------
greeting  db  'HELLO'
len       db  5 
; --------------------------
CODESEG
start:
	mov ax, @data
	mov ds, ax
; --------------------------

    mov bx, offset greeting 
    mov al,[bx]
    mov ah,[bx+len-1]
    mov [bx],ah
    mov [bx+len-1],al
    mov al,[bx+1]
    mov ah,[bx+len-2]
    mov [bx+1],ah
    mov [bx+len-2],al

; --------------------------
exit:
	mov ax, 4c00h
	int 21h
END start