WHAT 8051, full ident please
MOVX @DPTR,#01h
is not an instruction for the '51, please state correctly.
For a 24 bit DPTR, you will need an extanded addressing device such as the Philips MX.

In assembly you will need a fetch routine such as:
;; fetch
;;
;; dptr must point to 16 lsb bits of address
;; r7 must point to 8 msb bits of address
;;
;; acc contain byte fetched

fetch:
push p1shadow
mov p1,r7
movx a,@dptr
pop p1shadow
ret


Erik