| 摘要 |
PURPOSE:To prevent a waiting state for a long time, by providing a timer with a plurality of devices connected to a communcation bus, and giving one more priority for usage request, if the usage request is not received even when a prescribed time is passed after each device mekes the usage request of communication bus. CONSTITUTION:Counter circuits 213, 223, 233 are provided in processors 21, 22, 23 connected to a communication bus 3. If a usage request from a communication bus usage request circuit 211 in the processor 21 is at lower rank then other processors, the usage request on a bus line 311 is waited at a bus controller 4. When a counter circuit 213 started at the same time as the production of the usage request detects a prescribed lapse of time, the usage request circuit 211 is given one more priority for the usage request and changes the transmission of usage request on a bus line 312. Thus, the communication bus usage request from a processor at lower rank can be prevented from being in a waiting state for a long time. |
