REQUEST CONTROLLING SYSTEM

PURPOSE:To prevent priority order from being fixed by setting an FF only of a device which occupies finally a bus, to ''1'', among each peripheral device connected annularly by an inquiry line, and executing an inquiry, in case when a request is received from each device in the next time, from the device of the following stage. CONSTITUTION:Plural peripheral devices DV1-DVn holding a common bus in common send out successively request inquiring signals E1-En to signal lines L1-Ln connected in the shape of a loop. Also, each peripheral device DV1- DVn sends out request signals R1-Rn and busy signals B1-Bn to a bus control device BC, and receives an approval signal AVL from the device BC. When a bus occupancy request signal Ri is sent from one device DVi, the bus control device BC sends out the available signal AVL when all the busy signals are in an L level. An FF of the device which occupies finally the bus set to ''1'', only the FF of this device is set, an inquiry signal Ek is sent out, the inquiry is stopped by the DVi, and the DVi occupies the bus. In this way, the priority order is prevented from being fixed.