This paper presents the real-time system software of an open architecture robot controller and some transputer programming issues related to the controller applications. The underlying design philosophy of the controller system software is to support the incorporation of user defined functional modules over an openly accessible transputer network in addition to the stand-alone operations. The controller system software combines an OS9 real time operating system kernel and a servo control dispatching scheme implemented in a device driver to support the multi tasking requirement. It provides flexibility and convenience for modern robotics research applications.