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Abstract

A system for providing fault-tolerant synchronized operation of the Time of Day (TOD) clocks of the respective data processors in a multiprocessor complex. Basically, the system is comprised of a duplex implementation having redundant TOD clock sources, and a plurality of TOD slaves which provide the TOD clocks in the associated processors. A register/counter in each TOD clock source is incremented by a high frequency signal to achieve the required TOD value resolution, and the latter signal is divided down to provide a lower reference frequency signal for synchronization of the clock sources. Each TOD slave includes terminals for receiving a pair of reference frequency signals and for trouble-free switching between the signals, as required. Alternatively, a quad implementation of clock sources which is substantially free of single points of failure of the synchronization mechanism is described. Frequency steering of the clock sources provides increased accuracy and conformity to real time when desired.

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First Claim