REAL-TIME CLOCK FOR CONSUMER DEVICES AND METHOD FOR IMPLEMENTING SUCH A CLOCK

摘要

Consumer electronic devices with the abibility to receive TV signals such as TV sets or video cassette recorders include a clock for programming said device. Such clocks are controlled by quartz crystals which have some tolerances, the compensation of which are normally done by trimmer capacitors. The real-time clock according to the invention uses the sync signals of the vertical synchronization of a TV picture for the comparison with the oscillation of the quartz crystal. In dependence on said comparison, correction values are calculated. Further a method for implementing a real-time clock in such a consumer device is given, wherein the real time is generated by adding time intervals of a prescribed length to the sum of former ones. For the correction of the so generated time, either a number of additional intervals is added if the real oscillator frequency is too low, or the adding of regular intervals is skipped for a number of intervals if the oscillator frequency is too high, wherein said number is computed by an internal processor of the device with the use of sync pulses included in the TV signal.