US Patent 7750497 Power feed control circuit for on-vehicle electronic control apparatuses

First and second on-vehicle electronic control apparatuses which communicate with each other through serial communication interface circuits are fed with powers through an output contact of a power source relay from an on-vehicle battery, an electromagnetic coil of the power source relay is energized through a transistor when a power source switch has been closed, first and second microprocessors are activated upon closure of the output contact, a first watchdog timer generates a self-holding command signal and keeps an operating state of the power source relay when intervals of a watchdog signal which is generated by the first microprocessor are normal, and the self-holding command signal is stopped to deenergize the power source relay, when the first and second on-vehicle electronic control apparatuses have completed their save processing steps in accordance with opening of the power source switch.