A data communication system for communicating data between a bus running at a first clock frequency and a circuit block operating synchronously with the data bus at a second clock frequency. The system includes a clock generator for generating a bus clock signal at the first clock frequency and a chip clock signal at the second clock frequency wherein the first and second clock signal frequencies are in the ratio of (N-1):N where N is an integer greater than 1 and wherein the bus and chip clock signals are synchronized once every N cycles of the chip clock signal. The clock generator also generates a synchronization signal indicating the chip clock signal cycle in which the bus and chip clock signals are synchronized. The circuit block includes an interface circuit for receiving and transmitting data on the bus. The system also includes circuits connected to each circuit block for identifying a chip clock signal cycle in which data cannot be transmitted by the circuit block on the bus and a chip clock signal cycle in which data cannot be received by the circuit block from the bus, there being one of each type of cycle in each contiguous block of N chip clock cycles.