DECISION CIRCUIT FOR FAULT MASKING

PURPOSE:To obtain a decision circuit with high reliability withstanding a fault by using a couple of logic gate blocks outputting a self-diagnosing signal switchingly so as to eliminate a processing result signal dissident with a decision signal by majority decision. CONSTITUTION:When a decision output from a changeover circuit section 6 and a processing signal from function modules (seven modules or the like) are coincident with each other, outputs 2a, 2b of plural switches 2 are respectively logical '0', '1' and in case of the dissident outputs, the outputs 2a, 2b are logical '1', '0' respectively and the result is given to a logic gate block 3. Then the block 3 eliminates the input 1 at the dissidence from the candidate of decision, and the block 3 outputs the result of decision 3a as logical '1' in case of seven or over of the inputs 1 and as logical '0' in case of six or below of the inputs 1, and outputs the result of self-diagnosing signal 3b. If the block 3 is decided to be faulty based on the signal 3b, the changeover circuit section 6 selects a logic gate block 4 similar to the block 3. Thus, the fault masking decision circuit with high reliability withstanding a fault is obtained.