| 摘要 |
PURPOSE:To improve the system reliability by using two circuits to control the switch of interface signals between a logic control circuit and an external device. CONSTITUTION:When no electric power is supplied to a switch control circuit 103 any more, a power fail signal 115 is delivered from the circuit 103. While an interruption request signal 216 is delivered via a switch control circuit 203 and an interruption input circuit 206. Thus a switch selection signal 212 and a device switch signal 218 are delivered through a logic control circuit 202 and the circuit 203. Then an interface signal switch circuit 204 and a device switch circuit 207 connect an interface signal 117 to interface signals 211 and 119 respectively. Here if an external device 301 is inactive, the circuit 202 detects the inactive state of the device 301 via the interface signal. Then the circuit 207 connects the signal 119 to the signal 21i and executes a job with an active external device 302.
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