A method of seamlessly switching over between the command mode and the video mode includes receiving a command for switching over from the command mode to the video mode; generating a sampling value by measuring a time interval between a point in time of an internal synchronization signal used in the command mode and a point in time of an external synchronization signal received in the video mode; generating a parameter for shifting the internal synchronization signal based on the sampling value; shifting the internal synchronization signal to synchronize with the external synchronization signal based on the parameter; and switching over from the command mode to the video mode when the internal synchronization signal of the command mode synchronizes with the external synchronization signal. According to the disclosure, while driving a display.