| 摘要 |
PURPOSE:To execute switching between a working system and a stand-by system surely, by switching a common memory independently of the operation of a preferentially selected circuit. CONSTITUTION:If one of processors 10-1n-1 executes an instruction to switch a common memory control device 2S of the stand-by system to a common memory control device 2A of the working system a signal is sent from the processor to the device 2S independently of the operation of a preferentially selected circuit 6, and a switching signal holding FF17 is set. Meanwhile, a switching timing circuit 18 starts a refresh timing control circuit 20. Next, in case that the switching instruction and a memory refresh request contend, the output of the FF17 is sent to a state display FF10 to rest it just after the completion of the refresh operation. Meanwhile, the circuit 20 sends a signal to a refresh request circuit 19 and a memory control circuit 8 and freezes operations of circuits 19 and 8 from the switching start time to a proper time after switching finish time. |
