first it is /pre not pre

your LD_8802: needs to be a subroutine like SEND_SERIAL
just add a RET after it. Didn't you have a program where the RS232 was OK?


more like this

; configure the UART ADuC812
    MOV     SCON,#52h  ; configure UART for 9600baud..
    MOV     TMOD,#20h  ; ..assuming 11.0592MHz crystal
    MOV     TH1,#-3
    SETB    TR1       	; ok this works

MAINLOOP:

;... THIS THE RIGHT PLACE FOR THIS?.....................		
    JNB     RI,$        ; Recive serial data
    MOV     40H,SBUF    ; Store data in IN MEMORY

    JNB     RI,$        ; Recive serial data
    MOV     42H,SBUF    ; Store data in IN MEMORY
;.........................................................

;Do Check SUM
   AJMP MAINLOOP  ; Start over if bad

;CSUM GOOD 
; move address and data into R0,R1
   ACALL LD_8802;
; repeat for all DACs

   AJMP MAINLOOP  ; Start over

LD_8802:
		ORL	P2,#11110000B 	;SET CLK,CS,SHDN HIGH
		CLR	P2.5		;SET CHIP SELECT LOW
		MOV	LOOPCOUNT,#4	;ADDRESS IS 4 BITS
		MOV	A,R0	        ;GET DAC ADDRESS
		RR	A		;ROTATE THE DAC
		RR	A		;ADDRESS TO MOST
		RR	A		;SIGNIFCANT BIT (MSB)
		RR	A
		ACALL	SEND_SERIAL	;SEND THE ADDRESS
		MOV	LOOPCOUNT,#8	;DO 8 BIT OF DATA
		MOV	A,R1
		ACALL	SEND_SERIAL	;SEND THE DATA
		SETB	P2.5		;SET CS HIGH
                RET			;DONE


SEND_SERIAL:	RLC	A	;MOVE NEXT BIT TO CARRY
                CPL	LED	;BLINK LED
                MOV	P2.7,C	;MOVE DATA TO SDI
                CLR 	P2.6	;PULSE THE
                SETB	P2.6	;CLK INPUT
                DJNZ	LOOPCOUNT,SEND_SERIAL ;LOOP IF NOT DONE
                RET				;DONE
                END