Design of a Self-Checking Microprocessor for Real-Time Applications

Abstract

This paper deals with the design of a microprocessor dedicated to safety applications and more particularly to Automatic Train Control. This microprocessor is self-checking i.e. able to detect its own errors. Its name is COBRA for Controller with Built in self-checking for RealTime Applications.In the design of this circuit, low-level fault hypotheses for the N-MOS technology are considered. In this case redundant faults, i.e. undetectable faults, generally exist in any design and thus fault detecting capabilities must be provided for sequences of faults. The functional circuits will process with coded data and will be checked by Strongly Code Disjoint Checkers.COBRA is a microprocessor-type device, its data path processes independently 19 different signals: date out external events, measure frequencies, and supervise 14 level inputs (binary values). 7 independent outputs could be binary values, or clocks, for 3 of them. The data path communicates with an external PROM, used as program storage for COBRA. This PROM is addressed with 14 bits, multiplexed over the 8-bit address/data internal bus of the data path. It contains also one serial I/0, a 64 byte RAM, and 3 independent 14 bits counters. An 8 bit ALU could be used for arithmetical or logical operations. A set of 42 instructions processes all these operations.