BUS CONNECTION CONTROL SYSTEM

摘要

PURPOSE:To prevent system breakdown by switching a bus to a both-system high-order device from a low-order device for inquiry when an act signal line is at fault, and connecting the low-order device and an act-system high-order device via a bus after confirming the act of the high-order device. CONSTITUTION:An act signal line 9 has a fault and a 0-system high-order device 1 is set under a stand-by state together with an active 1-system high-order device 2 in an act fixed state. Under such conditions, the signal lines 9 and 10 go to active. When an act signal line monitor circuit 7 of a low-order device 3 detects an act of a signal line, the circuit 7 issues an instruction to a processor Pr6 and an inquiry to a Pr4 of the device 1 via a bus 11. Thus the Pr4 answers a stand-by state. The Pr6 connects both devices 2 and 3 via a bus 12 by a bus switching circuit 8 and an inquiry to a Pr5 of the device 2 is generated, then Pr5 answers an act. Then the Pr6 recognizes that the device 2 is active and transfers data via the bus 12. Thus the system breakdown can be prevented.