The AD724 accepts either FSC or 4FSC clock. When a clock is not available, a low cost parallel-resonant crystal (3.58 MHz (NTSC) or 4.43 MHz (PAL)) and the AD724's on-chip oscillator generate the necessary subcarrier clock. The AD724 also accepts the subcarrier clock from an external video source. The interface to graphics controllers is simple: an on-chip logic "XNOR" accepts the available vertical (VSYNC) and horizontal sync (HSYNC) signals and creates the composite sync (CSYNC) signal on-chip. If available, the AD724 will also accept a standard CSYNC signal by connecting VSYNC to Logic HI and applying CSYNC to the HSYNC pin. The AD724 contains decoding logic to identify valid horizontal sync pulses for correct burst insertion.