MainLoop:   CLR   RI0               ; Acknowledge any recent Rx bytes

            SETB  LED               ; Turn output on
StillOn:    DEC   A                 ; Count down from OnTime (in SBUF)
            CJNE  A,#0,StillOn      ;  to zero

            CLR   LED               ; Turn output off
StillOff:   DEC   A                 ; Count down from 255 to OnTime
            CJNE  A,SBUF,StillOff   ;  (in SBUF)

            JMP   MainLoop          ; Repeat forever