The KS2508 is used to display some characters or symbols on a screen of monitor. Basically, the operation is to control the internal memory on chip and generate the R,G,B signals for some characters or symbols. The R,G,B signals are synchronized with the horizontal sync. Then the R,G,B signals are mixed with the main video signal in the Video Amp IC. The font data for characters or symbols are stored in the internal ROM. This stored data are accessed and controlled by the control data from a micro controller. The control data are transmitted through the I2C bus. All timing control signals including the system clock are synchronized with the horizontal sync. Therefore there is a PLL circuitry on chip.