An IC card, as a portable medium, has an oscillator for generating a low-frequency clock signal for time-piece. A display clock for display is provided for counting the clock signal. The time based on a count carried out by the display clock is displayed on the IC card a display section. In this case,...http://www.google.es/patents/US4766294?utm_source=gb-gplus-sharePatente US4766294 - Portable medium
