STEP-NC is a new model for data transfer between CAD/CAM and CNC that allows specifying machining process rather that tool motion with respect to the machine axes. STEP-NC CNC controllers are a new breed of CNC controllers that allow using this high-level model for a seamless integration in the CAD-CAM-CNC chain. Various prototypes of STEP-NC CNC controllers have been developed so far, mainly based on industrial PCs. In this paper we instead show how it is possible to realize a STEP-NC CNC controller using a low cost microcontroller, embedded in the CNC machine; this goal has been obtained by accurately parallelizing the tasks involved in the machining process. More precisely, this paper presents the design and realization of an embedded system able to control a CNC machine with two degrees of freedom, to machine STEP-NC part programs and to perform also other high level activities.