Abstract: An improved demodulator recovers data symbols from a serial data stream comprising digital bits and outputs said data symbol in parallel data format. The demodulator includes sampling means to take multiple samples of each data bit in the received serial data stream, correcting any irregularity in the duration of the bit, and from those samples reconstructs a parallel data stream. A companion modulator serves to transform a parallel data stream in the serial data form. Together the modulator and demodulator are formed within a single substrate of semiconductor material. The modulator demodulator serves preferably as elements of a media access controller for a fiber optic transmission system that transmits data at rates of 100 Mhz.