ELECTRONIC CONTROLLER AND ITS DESIGNING METHOD

摘要

PROBLEM TO BE SOLVED: To securely prevent damage to a controlled system caused by a runaway of a microcomputer without adding any special hardware. SOLUTION: The electronic controller is equipped with the microcomputer which outputs a signal for controlling the electrification of an electric load and an abnormality monitor circuit which monitors the watchdog clear signal from the microcomputer and outputs a reset signal for a certain time Tr once detecting the runaway; and the time Tr and the time of abnormality decision making by the abnormality monitor circuit are so set that if the microcomputer does not recovers to the normal state from the runaway state even after receiving the reset signal, 'T2/T1' corresponding to the unstable output time rate of the microcomputer in the mentioned state is smaller than the permissible electrification time rate of the electric load, where T1 is a cycle of the reset signal repeatedly outputted from the abnormality monitor circuit to the microcomputer and T2 is the time obtained by subtracting the certain time from the cycle T1.