AJMP START
        
START:  MOV TMOD,#20h
        MOV SCON,#50h
        MOV TH1,#0F4h
        MOV TL1,#0F4h
        SETB TR1

        MOV COUNTER,#01h    ;init counter
        CLR RECEIVED
        CLR VALID_TAG
        SETB P2.0                ;the LED must be in off state

FIRST_BYTE:     <b>JB TI,TRANS</b>      ;if transmission is over jump to trans
                MOV A,SBUF
                CJNE A,#0Ah,LAST_BYTE   ;check first byte
                MOV COUNTER,#01h
                <b>AJMP RECEV</b>