| 摘要 |
PROBLEM TO BE SOLVED: To enable respective devices to respectively appropriately access a shared bus by calculating the rate of the shared bus to be used by plural devices and changing priority corresponding to the calculated result. SOLUTION: When the total of bus occupancy rates of DMA control parts 1-3 calculated by a bus monitor part 8 on the basis of bus use permission signals ack1-ack3 exceeds a predetermined threshold value and a control change signal CHS is made active, in a priority determining part 18, a priority table is changed from first table to second table. Thus, when the use rate of a bus 5 is high, the priority of an access control part 4 having the lowest priority is improved so that a CPU 14 can surely access the bus 5. Namely, the DMA control parts 1-3 and the access control part 4 can respectively appropriately access the bus 5.
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