| 摘要 |
PURPOSE:To reduce the cost of a small scale electronic device while keeping it small in size and light in weight by writing stored contents of a volatile memory in a non-volatile memory only at the time of a power failure and using the small-sized, light-weight, and inexpensive non-volatile memory as a backup memory. CONSTITUTION:A backup circuit 10 where the operating voltage of a system is held only for a certain time at the time of a power failure, a voltage detector 13 which detects the power failure by the voltage reduction of a power source, and a rewritable no-volatile memory 12 are provided, and stored contents of the volatile memory in an MPU 11 are written in the memory 12 by the operating voltage held in the backup circuit 10 at the time of detecting the power failure by the voltage detector 13, and written contents of the memory 12 are read out and are written back to the volatile memory at the time of power restoration. Consequently, stored contents of the volatile memory are written in the non-volatile memory 12 only when the power failure is detected by the voltage detector 13. Thus, write to the non-volatile memory 12 is rare, and the non-volatile memory 12 which is small in size, light in weight, and inexpensive but has the write frequency limited can be used as the backup memory. |
