DATA SEGMENT
        A DB 50H
        B DB 60H
DATA ENDS

CODE SEGMENT

        ASSUME DS:DATA,CS:CODE
        START:
                MOV AX,DATA
                MOV DS,AX

                MOV AL,A      
                MOV AH,B
                MOV BL,AL
                MOV AL,AH
                MOV AH,BL
                MOV A,AL
                MOV B,AH

                MOV AX,4C00H
                INT 21H

CODE ENDS
        END START

OUTPUT
***********

 BEFOR           AFTER
 ax 0000        ax 06C1
 bx 0000        bx CD36