A variable clock control information generator receives vertical blank interval information corresponding to a vertical blank interval (VBI) during display rasterization. The vertical blank interval is a period of time in a video display signal that temporarily suspends transmission of video data as is known during display rasterization, to allow a display to return back up to (retrace) the first line of the display after scanning the end of the display. In response to the received vertical blank interval information, the variable clock control information generator produces memory clock control information to change the frequency of a memory clock divider signal during the detected vertical blank interval.