| 摘要 |
PURPOSE:To enable each master device to use a common bus almost equally, by providing a means which nullifies the next common bus use request of a device itself having a common bus right of using, and sets it at a standby state. CONSTITUTION:A gate circuit 14 inserted to a bus priority request line 20 between an arbitration control circuit 13 and a priority decision circuit 16 performs the ON/OFF control of the line 20 by a control circuit 17. A gate circuit 15 inserted between the arbitration control circuit 13 and a common bus request line 9 performs the ON/OFF control of the line 9 to the circuit 13 by the control circuit 17. In a case where the master device 1 having the highest priority issues a bus request again after acquiring a common bus line 4 and completing transfer, and when another master device 12 never uses the common bus in spite of issuing the use request, both a bus use permission line 19 and the line 9 are set at (1)s, therefore, both the gate circuits 14 and 15 are turned OFF by the control circuit 17, and thereby, the bus use request of the master device 1 is nullified, and is set at the standby state. And at a time when no device driving the line 9 exists any more, the master device 1 is permitted to use the common bus line 4. |
