Abstract: A simulation model is provided which comprises a combination of the physical device to be modeled and means for controlling the physical device at normal operating speeds so as to avoid loss of data or of accumulated functions. Specifically, the physical device to be modeled is connected through a micro-system simulation means which can accept any of a wide variety of external devices and which includes the logic circuitry and control means necessary to allow the physical device to be stimulated and the resulting behavior observed under external control. Data and logic state patterns are preserved by effective control of the starting, stopping, cycling and resetting of the physical device.