Abstract
This paper describes a method to construct the logical circuit based on the fail-safe concept. As the actual device to realize the fail-safe three valued logic, C-type fail-safe logical circuits are developed by the author, the key component of which is fail-safe threshold logical operational oscillator composed of resistors and semiconductors.
In these circuits the truth values 1, 0 and 1/2 correspond to the voltages +V, -V(|V|>|E|, ±E: threshold voltage) and v(|E|≥|v|≥0), respectively. The logical functions are expanded in the canonical forms and the logical circuits to form a complemental system by themselves are completed by the use of fundamental elements.
Because the fundamental circuits for this system can be easily integrated, a highly reliable fail-safe three-valued logic system is considered to be obtained.
In the system using C-type fail-safe logical circuits, the output signal carries not only logical information but also the checking signal. If the voltage corresponding to either 1 or 0 appears at the output, it means that there is no failure in the circuits and that the system is normally operating. Therefore, no special device is needed to check the system.
