check this program , they tell me



START: ORG 0000H
MOV SCON,#52H
MOV PCON,#0
MOV TH1,#253
MOV TMOD,#20H
SETB TR1
RXBUF: JNB RI,RXBUF
CLR RI
MOV A,SBUF
MOV DPTR,#4000H
MOVX @DPTR,A
MOVX A,@DPTR
MOV DPTR,#5000H
MOVX @DPTR,A
MOVX A,@DPTR
MOV SBUF,A
TXBUF: JNB TI,TXBUF
CLR TI
SJMP RXBUF
END