| 摘要 |
PURPOSE: A method for arbitrating a bus, based on priority arrangement, is provided to control the priority according to a use history and thereby arbitrate a VME bus fairly, in case that several bus arbitrators with a fixed priority fashion shares a use request level. CONSTITUTION: When the VME bus begins to be used, bus grant signals(bg0-bg3) are sent to bus requesters having a certain level that is not the lowest level, in case that the bus requesters which have the certain level and a level lower than the certain level exist. A bus arbitrator checks the priority between the bus grant signals(bg0-bg3) generated by the bus requesters when the time of using the VME bus ends. If there is a bus request signal having a level lower than those of bus request signals, which are equal to the bus grant signals(bg0-bg3), the bus grant signals(bg0-bg3) are given to a bus requester that has a higher priority than the bus requests with a low level has. When the bus grant signals(bg0-bg3) of the VME bus end, the bus grant signals(bg0-bg3) are given to the bus requests which have a higher level than the VEM bus has.
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