US Patent 7664213 Clock alignment detection from single reference

A data communications system is disclosed. The data communications system comprises two clock domains. Each of the clock domains are coupled to receive a source clock signal. The first clock domain includes a first clock signal and the second clock domain includes a second clock signal, each of the first clock signal and the second clock signal are derived from the source clock signal. The first clock signal has a frequency which is different from that of the second clock signal, and which is not an integer multiple of the frequency of the second clock signal. The first clock domain includes circuitry which is configured to generate both the first clock signal and a reference clock signal derived from the source clock signal. The first clock domain is further configured to utilize the first clock signal to sample the reference clock signal, and assert an aligned signal responsive to detecting an edge of the reference clock signal, wherein the aligned signal indicates an edge of the first clock signal is aligned with an edge of the second clock signal.