Hard:
You can use some dallas devices. Battery baked memories.

Soft:
...Your program...
;Save routine
mov r0,#1st_internal_adress
mov dptr,#1st_external_adress
mov b,#number_of_bytes
loop:
mov a,#@r0
movx @dptr,a
inc r0
inc dptr
djnz b,loop
ret

;Load routine
mov r0,#1st_internal_adress
mov dptr,#1st_external_adress
mov b,#number_of_bytes
loop:
movx a,@dptr
mov #@r0,a
inc r0
inc dptr
djnz b,loop
ret