A hardware-oriented interpolator for an N/C lathe is developed so as to generate control commands for the servo unit of the lathe. The hardware is implemented around the digital differential analyzer (DDA) together with its driving software to be compatible with Motorola``s 16-bit $\mu$-processor, MC-68000. The interpolator realized in this way included two basic functions, i.e., linear interpolation and circular interpolation. Regarding these types of interpolation, various functional requirements and associated problems are investigated.