| 摘要 |
PURPOSE:To secure a system bus in an approximately even way despite the connection of many boards for DMA transfer, by changing the set value of a timer which discontinues the operation of a DMA controller in accordance with the using state of the system bus. CONSTITUTION:When the 1st DMA transfer is through, the bus using state is checked by a bus state monitor circuit 8 after an extremely small time (timer b). If the bus is used by another DMA transfer controller (BBSY=1), a timer (C) of a long time is actuated again for the 2nd DMA transfer. While the 2nd DMA transfer is carried out without actuating the timer C in case the bus is not used by another DMA transfer controller (BBSY=0).
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