Bus system wherein a bus-using request signal is issued in advance of a determination that a bus is to be used and is thereafter cancelled if the bus is not used

摘要

A method is provided for controlling bus-using rights in a multi-bus system which has a plurality of buses and a plurality of units connected to each of the buses. A unit connected to one bus is accessible by another unit connected to another bus. When a first unit accesses either a second unit on the one bus or a third unit on another bus, two requests for use of the one and another buses are issued substantially at the same time, thereby reducing the time taken for acquiring a bus-using right of the another bus. As soon as it is found that access is directed to the second unit on the one bus, the request for using the another bus is canceled, thus reducing a bus occupation rate for the another bus.