AUXILIARY DEVICE FOR CENTRAL PROCESSING UNIT

摘要

PROBLEM TO BE SOLVED: To secure the operation of a CPU with highly reliable fail-safe by switching to the operation by the other CPU by absolute minimum circuit constitution even in the case that the operation power source of one CPU is abnormal. SOLUTION: An auxiliary CPU 13 operated by power supply from a second power source circuit 14 similarly to the fact that a normal CPU 11 is operated by the power supply from a first power source circuit 12 is provided and also a switching circuit 21 for selecting which one of processing signals by the CPUs 11 and 13 is to be outputted to a device main body is provided. The auxiliary CPU 13 monitors a power supply voltage to the normal CPU 11 at an AD port 13a and sends out a reset signal to the normal CPU 11 when it becomes lower than a preset threshold. The switching circuit 21 switches a control signal to be outputted to the device main body from the processing signal by the normal CPU 11 to the processing signal by the auxiliary CPU 13 at the time of receiving the reset signal.