a bus system for exchanging information between a plurality of circuits connected to the system . the bus system includes a polling bus , a message bus , and a bus controller . the bus controller polls each circuit to see if the circuits require access to the message bus . information between the circuits is conveyed by first transmitting the information to the bus controller where it is temporarily stored . that information is then sent to the destination circuit by the bus controller . information is thus conveyed over the message bus twice for every exchange of informaton between two circuits .