Abstract: A clock integrated circuit comprises an oscillator circuit for producing a basic frequency signal, a frequency divider for frequency dividing the basic frequency signal to a predetermined frequency, a time measuring circuit for counting output pulses from the frequency divider to produce time data consisting of 1-second, 10-seconds, 1-minute, 10-minutes, 1-hour and 10-hours digits or a combination of some of these digits and a display driver circuit for displaying the time data on an external display means. Further, it comprises a digit selection circuit which outputs the afore-said time data such that the time data can be directly coupled to a central processing element.