Abstract: A digital circuit simulator for simulating data handling operations of a digital circuit includes a primary simulator operable in response to simulation instructions in a first programming language, and a plurality of simulation blocks for simulating data handling operations of respective sections of the digital circuit. Each simulation block is operable to receive external input data from the primary simulator, internal input data from another of the simulation blocks, or both. A data interface is arranged to exchange data with the primary simulator and the simulation blocks and is operable to supply external input data from the primary simulator to one or more simulation blocks, and to supply external output data from a simulation block to the primary simulator, and to supply internal output data from a simulation block to one or more other simulation blocks.

Abstract: A primary circuit model using a primary simulator 40' operates in conjunction with a plurality of secondary circuit models 10, 20, 30 using a secondary simulator 100. Only signals external to the secondary circuit models are passed between the primary simulator and the secondary simulator. The primary simulator and the secondary simulator independently increment their simulated time when they are active. The secondary simulator is invoked when a signal to which one of the secondary circuit models is responsive is changed by the primary simulator. The secondary simulator is not exited until no further signal changes are being driven by the secondary circuit models at which stage the last asserted values of signals changed by the secondary circuit models are returned to the primary model.