PROGRAMMABLE CONTROLLER

摘要

PURPOSE:To provide the programmable controller which can hold the contents of a memory for arithmetic without backing up the controller by a battery at the time of a power source disconnection. CONSTITUTION:If an input voltage drops below a monitor voltage at the time of the power source disconnection, a power failure predicting circuit 6 supplies a power failure prediction signal S1 to a CPU 1. The CPU 1 performs interrupting operation with this power failure prediction signal S1 and writes the data from the RAM 3 for arithmetic in a stand-by EEPROM 5. The power failure predicting circuit 6 supplies the CPU 1 with a reset signal S2 a delay time after the generation of the power failure prediction signal S1 to reset the CPU 1. The CPU 1 after being initialized transfers the data held in the stand-by EEPROM 5 to the RAM 3 for arithmetic to reproduce the data in the RAM 3 for arithmetic before the power source disconnection.