SERIAL:	
;;;;;;; push the registers used
                JNB RB8,GET_DATA	;Jump if RB8=0 means data
;;;;;;; use a instead of b, then you can do a cjne
		MOV B,SBUF		;Move the copy to Accumulator
		CJNE B,#001H,GO_ON	;Compare the Address if its equal to 001H then
		CLR SM2			;Clear the SM2 to get the data
;;;;;;;; move GO_ON to the last reti, it is advisable to have only one exit point
GO_ON:		RETI			;Return back from ISR
GET_DATA:	MOV A,SBUF		;Get the copy to Accumulator
;;;;;;;; move a to a variable for main to see
;;;;;;;; here you need setb, NOT clr
		CLR SM2			;Clear the SM2 for agian for the Address
;;;;;;;; pop the registers used
		RETI			;Return

this will (almost) work if you only have one data byte.

Erik