Mike,

Is ALE tied to Pin #11 of 74LS373? Is pin #1 tied to GND?

Also you need a delay of at least 50 mSec between the statements:

ORG 00H
AGAIN:
MOV A, #0AAH ; LOAD A WITH AAh VALUE
MOV DPTR, #0000H ; LOAD ADDRESS IN DPTR
MOV 8EH, #00000011B ; SET EXTERNAL RAM ACCESS
MOVX @DPTR, A ; MOV AA out to 0000h
CALL DELAY_50mSec
MOV A, #00H ; clear out A
MOVX A, @DPTR ; move AAh back into A
CALL DELAY_50mSec
JMP AGAIN ; keep doing it
END

Regards,

Jacob