A clock circuit for outputting serial data without using a PLL is described. The clock is a VCO designed to start at a frequency that is slightly higher than necessary to preserve the data. The frequency of the clock is measured and if the frequency is too high or too low the DC control voltage for the VCO is changed to bring the VCO frequency back to the start frequency. Clock counters, holding registers, comparators, and a D/A form a feed back path around a VCO. In addition, a word boundary generator is used to define individual data words. The word boundary is formed by the absence of a bit clock transition while there is a data bit transition. A high/low threshold may be used where the VCO frequency, as measured, must transcend a threshold before the DC control voltage to the VCO is changed.