7.3.20.4 External Timing

In external timing mode, the pattern generator passes the incoming DE, HS, and VS signals unmodified to the video control outputs after a two pixel clock delay. The pattern generator extracts the active frame dimensions from the incoming signals to properly scale the brightness patterns. If the incoming video stream does not use the VS signal, the pattern generator determines the vertical blank time by detecting a long period of pixel clocks without deassertion.