The Video Timing Controller has six optional inputs for detecting the timing of the input video signal: vertical blank, vertical synchronization, horizontal blank, horizontal synchronization, active video and active chroma. The minimum set of inputs required to detect is either vertical blank, horizontal blank and active video or vertical sync, horizontal sync and active video. To enable detection, the Enable Detection GUI parameter must be set, and the control register bit 1 must also be set. The GUI parameter allows saving FPGA resources. The Control Register allows run-time flexibility. Other GUI parameters can be set to selectively disable detection of one or more input video timing signals.
The detected polarity of each input signal is shown by bits 0-5 of the Detection Polarity Register (address offset 0x2C). High denotes active-High polarity, and Low denotes active-Low polarity. Bits 8 and 9 of the Detection Encoding Register shows the number of lines skipped between each active chroma line. Bit 8 High denotes that every other line is skipped (4:2:0), and Low denotes that no lines are skipped (4:4:4 or 4:2:2). Bit 9 High denotes that every other pixel is skipped, and Low denotes that no pixels are skipped.
If any input ( vblank_in , vsync_in , hblank_in , hsync_in , active_video_in , active_chroma_in ) is not driven or is not connected, then detection for that input must be disabled. To disable detection for an input, deselect the appropriate option in the GUI ("Vertical Blank Detection", "Vertical Sync Detection", etc.).
A minimum set of signals that must be present for the core to properly detect the input timing and regenerate it. You must select these in the Timing Detection section of the core interface and also provide these signals when connecting the core. You can use the Active Chroma option with any of the combinations listed below. This option can regenerate Vertical Blank, Horizontal Blank, and Active Video if you provide the following inputs:
• Vertical Sync, Horizontal Sync, and Active Video
• Vertical Blank, Horizontal Blank, Vertical Sync, Horizontal Sync, and Active Video