1 Designing Circuits Detecting Different Types of Faults1

Abstract:- This paper presents methods for designing totally self-checking Mealy type synchronous sequential circuits (SSCs). We use implementations of the output and next state functions that are monotonic in state variables. The monotony enables the SSC to react to permanent faults differently than it does to transient faults. If the fault is permanent, the SSC will produce a non-code output after a number of clock cycles (latency), and the non-code output will be detected as an error by the checker. In the case of a transient fault, the SSC is able to become fault free after a number of clock cycles (so-called self-healing time). In the case of a permanent fault the minimal latency is desired. Though the self-healing of SSC after a transient fault takes its time. Thus, requirements to the period of the SSC functioning in cases of permanent and transient faults are contradicting. We propose a universal architecture of self-checking SSCs enabling to overcome the above contradiction. Namely, this architecture can be adapted either for reduction of the latency of a permanent fault or for increasing the SSC self-healing ability after a transient fault. In the proposed architecture, a method for SSC synthesis is presented. This method is oriented to FPGA based implementation. Key-Words:- On-line testing, sequential circuits, fault detecting, latency, transient fault, self