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Abstract

A system for checking a malfunction in a controller. The controller includes a microcomputer connected between an input and output terminal of the controller. The microcomputer is programmed to perform a normal control mode, to perform a self-checking mode, and to judge whether conditions of entry into the self-checking mode are met so as to select one of the two modes. An external circuit is connected between the input and output terminals of the controller so as to establish a predetermined relation between the voltage levels of the input and output terminals. In the self-checking mode, the microcomputer outputs a control signal for setting the output terminal to one of high and low logic voltage levels. The microcomputer judges whether an input signal passed to the microcomputer through the input terminal having the predetermined voltage relation with said output terminal has a voltage level corresponding to the voltage level of said output terminal, and judges that there is a malfunction if the input signal is not at the above-mentioned corresponding level. The microcomputer causes the malfunction to be displayed in an external display unit when the microcomputer judges the malfunction.

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First Claim