An apparatus for controlling a mechanical system in response to messages from a host computer system. The apparatus includes a conventional communications link for communicating messages from the host computer system to a motion control processor and interface and driver circuits for converting digital signals generated by the motion control processor in response to messages from the host computer system into control signals having appropriate waveforms and timing for controlling a particular mechanical system. The motion control processor is programmed to perform a number of tasks in accordance with a schedule downloaded from the host computer system. The host computer system downloads profiles which consist of series of segments consisting of data structures which define elements in the mechanical system to be controlled, identify functions to be performed and include necessary data. Tasks performed by the motion control processor include a communications interface task for handling messages from the host data system, a profile handler task for executing profiles, a motion control task for controlling motors in the mechanical system, and a read sensors task for reading sensor in the mechanical system. Other conventional, non-critical tasks may be performed by the motion control processor on a less frequently scheduled basis or in a background mode of operation. New profiles, schedules, and tick period duration may be down loaded from the host computer system dynamically, during operation of the mechanical system to provide highly flexible, adaptive control of the mechanical system.