PURPOSE: To cancel a period when the potential of a bus is unstable without using a resistor by detecting that any processors connected to one bus do not emit a bus acquirement request and driving the bus at every time.
CONSTITUTION: A refresh interval timer 3 outputs a refresh request signal at every prescribed time, and FF9 operates by the same clock signal as FF5. The output terminal of FF9 is connected to the respective input terminals of a NAND circuit 7 and an access control circuit 8. The output terminal of a NOR circuit 2 is connected to FF5. The output terminal of FF5 is connected to a driver 6 driving the bus BUS. The bus is driven in respective periods when a REQOP signal becomes 'H' in spite of the refresh request signal REFRQ from the timer 3 by constituting the input signal of FF5 only by the output signal of the NOR circuit 2. Thus, the instability of potential when the bus is not used is cancelled.
OGURA KIMINARI
KIKUCHI WATARU
YAMAGUCHI TATSUYA
