As soon as there are two bus initiators there are problems, for what happens when both initiators attempt to assert control signals? In order to avoid chaos, only one bus initiator should have control of the bus at any time. One scheme is for there to be a bus busy wire. Any device that acts as a bus initiator sets this wire to 1 as a flag for all other potential bus initiators to see. If any would-be initiator sees that the bus is busy, it defers action until the wire changes to 0.