| 摘要 |
<p>PURPOSE:To prevent malfunction when a main power source is turned on and off by inhibiting a circuit which is powered on by a subordinate power unit from operating except in a period specified by a controller. CONSTITUTION:A control changeover circuit 204 operates a main power source 201 in the backup system 210 of the electronic equipment and a chip is selected by an AND gate 302 and a shift register 301 in the system 210. Then, a backup circuit 211 is selected by holding a data input to the register 301 from a signal line (d) high by a CPU system 202 and then shifting it. The backup system 210 is allowed to operated only during the period of this chip selection. Consequently, the CPU system 202 when released from a reset state in the power-on operation of the main power source selects the chip of the backup circuit 211 and if an interruption from a voltage detecting circuit 205 is initiated, data is saved and then the chip select state in reset.</p> |
