Malfunction checking system for controller

A system for checking a malfunction in a controller, comprising:

• (a) at least one input terminal;
• (b) at least one output terminal;
• (c) an external circuit means being connectable between said input terminal and said output terminal so as to establish a predetermined relation between the voltage levels of said input and output terminals;
• (d) an external display means being connectable to said controller;
• (e) a microcomputer being connected between said input terminal and said output terminal;
• said microcomputer comprising;
• i) means for performing a normal control mode,
• ii) means for performing a self-checking mode, said self-checking mode performing means comprising an output control means for outputting a control signal for setting said output terminal to one of high and low logic voltage levels;
• a malfunction judging means for judging whether an input signal passed to said microcomputer through said 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 for judging that there is a malfunction if said input signal is not at said corresponding level;
• and a display control means for displaying said malfunction in said external display means when said malfunction judging means judges said malfunction, and
• iii) means for judging whether conditions of entry into the self-checking mode are met and for selecting one of said two modes;
• and
• (f) a reset means being connected to said microcomputer;
• said reset means refraining from outputting a reset signal during the time when said reset means is being supplied with a program run signal from said microcomputer;
• said reset means outputting said reset signal to said microcomputer so as to reset said microcomputer when said reset means does not receive said program run signal for a predetermined period of time;
• said normal mode performing means of said microcomputer including means for outputting said program run signal;
• said self-checking mode performing means including means for maintaining a no-operation condition at a final stage so as to wait for the reset signal from said reset means;
• and each time said microcomputer is reset in response to the reset signal said entry judging and mode selecting means first performs the entry judgment and the mode selection.