GB1310219A - Data clocking system - Google Patents

Abstract

1310219 Digital transmission; synchronizing INTERNATIONAL BUSINESS MACHINES CORP 5 Oct 1971 46177/71 Heading H4P A synchronizing system comprises a stored table with a look up system from which successive locations are read to provide selection of a plurality of sampling periods within each clocking period. A number of locations are scanned during each clocking period so that such period is extended or reduced, temporarily, until approximate synchronization is attained. The number of locations read is smaller or greater dependent on whether the clocking periods are advanced or retarded with respect to input signals. The basic clock period is divided into 31 sampling periods. When transitions of the sampling periods are slow relative to the incoming signals, e.g. input transitions occur in any of sample periods 1-14 the clock period is increased by one sampling period to 32 by which is maintained until the input signal is approximately synchronized, when it reverts to 31. Conversely if the clocking signal is fast the clock period is shortened to one having 30 sample periods. In practice clock period alteration is delayed until a number, e.g. 3 slow or fast successive clocking signals are detected. The phase of clocking signals relative to input signals alters about 3% per cycle but this may be increased under starting conditions by forcing a number into a sample buffer included in sync. store (2), Fig. 2 (not shown). Input signals may be presented on a plurality of lines which may have differing speeds preferably multiples of each other hence adjustment may be made by the provision of divisors. The sync. store (2) performs also logical operations and generation of differing sampling periods. Such operations can be performed by an associative store of the type disclosed in Specification 1,218,406 using table look up techniques, initiation of operation being based on a comparison of the state of an input signal with its state at a prior time. Fig. 3 (not shown) illustrates a layout for the sync. store words occupying horizontal rows, each row being divided into tables.