Abstract: An ECU for executing serial communication via a transmission line has a driver circuit. The driver circuit includes an integrator for integrating a transmission signal and a power source for generating a current which corresponds to the integrated value of the transmission signal and releasing the current to the transmission line. A terminal circuit for receiving a constant current smaller than a maximum current that the driver circuit can discharge is connected to the transmission line. Since the amount of output current from the driver circuit is gradually changed, the generation of noise in the transmission line can be prevented. Further, since the voltage of the transmission line immediately changes to either a high or low level depending on the amount of output current, accurate data communication can be performed.

Abstract: In an engine automatic control system for a vehicle for automatically connecting an electric source with an engine starter and an ignition circuit in response to disengaging operation of a clutch device of the vehicle, for maintaining the ignition circuit conductive while the vehicle runs, and for automatically making the ignition circuit non-conductive when the vehicle is arrested, the engine control system comprises a setting circuit interposed between an ignition switch and the ignition circuit for selectively setting the engine control system to its operative condition and a cancelling switch coupled with the setting circuit for automatically cancelling the operative condition of the engine control system when an operator leaves the vehicle.