FAULT EFFECTS IN ASYNCHRONOUS SEQUENTIAL LOGIC-CIRCUITS

The paper demonstrates the effects of single stuck-at faults in Huffma n-model asynchronous sequential logic circuits (ASLCs). The fault effe cts include equivalent-state redundant faults, invalid-state redundant faults and state oscillations. Equivalent-state redundant faults in A SLCs may be generated by violation of the fundamental mode constraint noncritical races or delays. On the other hand, invalid-state redundan t faults are caused either by the existence of invalid states, or by i mproperly assigning the 'don't-care' terms. State oscillations are gen erally caused by the presence of critical races. Based on the fault ef fects, this paper presents a set of rules for synthesising oscillation -free ASLCs in the presence of faults. As far as synthesising testable ASLCs is concerned, the race-free UDC state assignment is much better than STT state assignment.