A digital clock is a type of clock that displays the time digitally; they are often incorporated into many kinds of devices such as cars, radios, televisions, computers, and cell phones.
This project uses an IC PCF1175CT, specialized for clock applications. PCF1175CT is a single chip, 4.19MHz CMOS clock circuit providing hour and minute functions with 12-hour or 24-hour mode. It is designed to drive a 4-digit multiplexed data (duplex) to the LCD (liquid crystal display), having 13 output pins to be used for 26 output signals.
Settings the time is controlled by the switches connecting the S1(hour) and S2(minute) pins to VSS. When S1 and S2 are connected to VSS at the same time, all LCD segments are switched ON. Releasing the switches S1 and S2 resets the display. The operation in 12-hour or 24-hour mode is selected by connecting the MODE pin to the VDD or VSS respectively. If the MODE pin is left open and a reset occurs, the mode will change from 12-hour to 24-hour mode or vice versa. Static or blinking colon can also be selected by connecting the FLASH pin to VSS or VDD respectively.