MEMORY BACKUP PROTECTING DEVICE

PURPOSE:To protect data in a backup RAM and also to simplify the circuit configuration. CONSTITUTION:When a CPU enters an operation state, it is decided in a step 100 whether or not an NMi terminal of the CPU is at Hi; when so, an advance to a step 200 is made and the CPU preforms processes of respective steps. When the source voltage is unstable at the start, writing to the backup RAM is prevented from being allowed although the voltage drops, and the data in the backup RAM can be protected. Further, the data protection of the RAM at this time can be facilitated by a circuit outside the CPU and program processing in the CPU. Therefore, the circuit configuration is simplified by the program processing without adding any circuit outside.