A display driver circuit includes a source driver configured to output display data to data lines, a controller configured to control the source driver, based on a synchronization signal, and a frequency adjusting circuit configured to extend a first time interval of the synchronization signal from a first length to a second length, such that time interval in which the display data is not output to the data lines is extended, when second image data are not received from an external device during a reference time interval after first image data are received from the external device, and shorten the first time interval, from the second length to a third length, when an instruction is received from the external device after the first time interval is extended to the second length.