Fault effects in asynchronous sequential logic circuits

The paper demostrates the effects of single stuck-at faults in Huffman-model asynchronous sequential logic circuits (ASLCs).The fault effects include equivalent-state redundant faults, invalid-state redundant faults and state oscillations. Equivalent-state redundant faults in ASLCs may be generated by violation of the fundamental mode constraint noncritical races or delays. On the other hand, invalid-state redundant faults are caused either by the existence of invalid states, or by improperly assigning the don't-care terms. State oscillations are generally caused by the presence of critical races. Based on the fault effects, this paper presents a set of rules for synthesizing oscillation-free ASLCs in the presence of faults. As far as synthesizing testable ASLCs is concerned, the race-free UDP state assignment is much better STT state assignment.