Behavioural modelling of asynchronous circuits

Asynchronous circuits are well suited to behavioural (“black box”) modelling. Their external structure consists simply of a set of input terminals and a set of output terminals. Asynchronous circuits are often designed to handshake with their environment; in such cases terminals are grouped into ports through which request and acknowledgement signals (as well as data) can be communicated. Using simple examples, we show a number of alternative models of asynchronous circuits. We explain the importance of considering not only the circuit but also its environment. We then describe three classes of asynchronous circuit namely speed-independent, delay-insensitive and handshaking circuits-and finally we look at the modelling and analysis of a toggle flip-flop as a small case study