Currently today, the vertical blanking interval lines of TV signals are used to carry digital information, e.g. teletext, pay TV, program marking. One part of this information can be the current real time. Often consumer products are equipped with a real time clock which is linked to a micro-controller driving the complete device, e.g. a VCR. This allows to perform some programming tasks. But this real time clock needs a power supply in order to work. In case of power failure, it looses the time unless it is backed up by an expensive accumulator or a battery. A central microcontroller (1) drives a real time clock (3) and the standby function of a power supply (4) . A data extractor (2) receives a signal containing the real time, e.g. a video signal, and extracts the expected data related to the real time and transfers this data to the microcontroller. The microcontroller sets the clock after preselected time periods, e.g. once per day, and after switching on the whole apparatus. The microcontroller and the real time clock only have to be supplied in stand by mode.