some simple example code to set you on your way, it works on the ADuC824B2, not too sure about your code, the 8052 core should be basically the same
it transmits and receives a single byte of data, just put in a loop for continious transmission and reception. the data in is sent out to port 2 also

ORG 00H
JMP MAIN

ORG 4BH
main:
MOV IE,#10h ; enable ES serial interrupt

cpl p3.4
mov R7,#0ffh
djnz R7,$
cpl p3.4


MOV SCON, #00h


mov sbuf, #55h

JNB TI,$

mov p2,sbuf

EN