Apparatus and method provide flexibility in generating a stimulation waveform to an electrode of an Implantable Neuro Stimulator (INS). The stimulation waveform is synthesized for each rate period interval. Each rate period interval is partitioned into time intervals, during which stimulation pulses, recharging, and time duration delays may be induced. With the embodiment of the invention, a second stimulation pulse, having different electrical characteristics than a first stimulation pulse, may be generated during the rate period interval. An embodiment utilizes apparatus comprising a waveform controller and a waveform generator that are controlled by the waveform controller. The waveform controller uses waveform parameters to instruct the waveform generator to form stimulation pulses. Any of the components may be adjusted or deleted in the generation of the stimulation waveform. The embodiment enables any of the associated waveform parameters to be updated at the waveform controller in order to alter the stimulation waveform.