A CATV system having a central facility connected through cables to a number of terminal units to establish two-way data communication. Each terminal unit includes a PLL that oscillates at a frequency corresponding to a channel selected. A frequency divider circuit subjects an output frequency of the PLL circuit to frequency division to provide a carrier frequency for an up-stream data signal. The central facility transmits programs and down-stream data signals through a plurality of channels. Each terminal unit transmits an up-stream data signal to the central facility by using an exclusive frequency corresponding to a channel selected.