Aspects disclosed in the detailed description include communicating low-speed and high-speed parallel bit streams over a high-speed serial bus. In one aspect, a data transmitting circuit converts a low-speed parallel bit stream into a high-speed parallel bit stream and then serializes the converted high-speed parallel bit stream based on a high-speed reference frequency. In another aspect, a data receiving circuit recovers the low-speed parallel bit stream from the high-speed parallel bit stream if the low-speed parallel bit stream is determined to exist in the high-speed parallel bit stream. By serializing and deserializing the low-speed parallel bit stream based on the high-speed reference frequency, it is possible to communicate the high-speed parallel bit stream and the low-speed parallel bit stream over the high-speed serial bus without requiring additional serializers and deserializers, thus reducing component costs and implementation complexities in both the transmitting circuit and the receiving circuit.