Externally hazard-free implementations of asynchronous control circuits

We present a new sum-of-product-based asynchronous architecture, called the N-SHOT architecture, that operates correctly under internal hazardous responses and guarantees hazard-freeness at the observable noninput signals. We formally prove that within this architecture, a very wide class of semimodular state graphs with input choices (either distributive or nondistributive) that satisfy the complete state coding property always admit a correct implementation. As with synchronous circuits, we permit internal hazards in the combinational logic core, which means that we can make use of conventional combinational logic minimization methods to produce the sum-of-product implementation. This represents a significant departure from most existing methods that require the combinational logic to be hazard-free and are mainly valid for distributive behaviors. We also present optimizations for this architecture which are related to state graph properties.