;swap between two varible with intermediate register
        .model small
        .stack 100h
        .data
            a db ?
            b db ?
        .code

            main proc

             mov a,'1'
             mov b,'2'

             ;before swap
             mov ah,02
             mov dl,a           ;1
             int 21h
             mov dl,b           ;2
             int 21h

             xchg dl,a        ;swap
             mov b,dl

             ;tab
             mov ah,02
             mov dl,09h
             int 21h

             ;after swap
             mov dl,a
             int 21h            ;2
             mov dl,b
             int 21h            ;1

           main endp
           end main