Abstract: A phase-locked loop with redundant reference input signals compares each reference input signal to the loop feedback signal to generate corresponding phase correction signals. In response to a reference select signal, one of the phase correction signals is selected for supply as a loop correction signal. The loop correction signal is supplied through a filter as a control signal to a VCO. Phase and frequency detectors are included, each detector receiving a corresponding reference input signal and connected to receive the loop feedback signal for generating a phase correction signal indicating the phase and frequency difference between the corresponding reference input signals and the output signal. Also, a selector is provided in communication with each of the detectors that selects one of the phase correction signals in response to the reference select signal as the loop correction signal.

Abstract: An apparatus for converting a frame code from a T-1 multiplexed data stream having a framing pattern in a first preselected format such as DMA-1, to a frame code in an output data stream having a framing pattern according to a second preselected format such as D2/D4. A data path is connected to receive the data stream for supplying the output data stream. Framing windows in the data stream are identified and modified by combining with a selected frame code modifier. The output data stream is then supplied to a T-1 receiver circuit adapted to the second preselected format.