A new scheme for macromodelling digital elements in the time domain is presented. Output waveforms and timing performances are predicted in detail, within an accuracy margin that depends mainly on the information available to describe the elements. A number pair (state, time-in-state) describe each individual element and, along with the macromodel of the element type, retain the necessary data to analyse the element at each time point. MASCOT (MAcro Simulator of Circuit Operation in the Time domain) is the set of programs incorporating the new concepts, and some results of analysis illustrate its use. Comparisons of run time between the new program and circuit-level simulators showed improvements of between two and three orders of magnitude.