A mobile device includes a display driver integrated circuit (DDI), a display panel, and an application processor. The DDI provides an internal synchronization signal based on an internal clock signal as a synchronization signal. The application processor calculates a time offset corresponding to a difference between a real time and the internal synchronization signal, and provides the time offset to the DDI. The DDI calculates a time to be displayed based on the time offset and a current time provided from the application processor, and displays the time to be displayed in the display panel in a self clock display mode.