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internal registers of the TVP7002

Michael Rivlin
Prodigy 225 points
Other Parts Discussed in Thread: TVP7002, THS8135

There are some ready-only registers In the TVP7002 which indicate resolution parameters: lines for frame (37h-38h), Hsyn width (3Bh), etc.

How can I convert , for example, data of register 3Bh to real width of Hsyn? For example, my input VGA has resolution DMT1660. For this resolution width of Hsyn is 1.185uS, or 192 (or C0h) pixels per Hsyn. But in the register "3Bh" I read the following data: 20 03 06 04 00 FA 01 3A. What relationship between 192 and this data?

Note. I use EVM THS8135 which use 27MHz oscillator for the TVP7002.

  • 0
    TI__Mastermind 43875 points

    Michael,

    Register 39h & 3Ah return the number of reference clocks for an ENTIRE line, which is much more useful than 3Bh, which returns only the size of the h-sync pulse.

    If you refer to the datasheet you will see that both these registers return the number of reference clock ticks between events. If you are using a 27MHz reference clock then the time of the specific event will be (REG / 27000000) seconds.If you are using the internal reference then it will be (REG / 6500000) seconds. Note though that if you are using the internal reference that it is not very accurate. This means that you need to include more guard band in your calculations when selecting what the detected resolution really is.

    You should also review the description for registers 37h & 38h which gives simplified examples of the mentioned registers for some common formats.

    Note that your software should include some guard band with all numbers since many VGA sources are not really 100% VESA compliant. Many sources do not send the correct H & V polarity, so if you can I suggest using only the total width and total lines as the primary measurements for determining the resolution.

    BR,

    Steve

  • 0 in reply to Steve Clynes
    Prodigy 225 points

    Thanks Steve.

    I've understood how to calculate width of horiyzontal and vertical pulses, and width of horiyzontal and vertical lines.

    But how can we get pixel rate?

    Regards,

    Michael

  • 0 in reply to Michael Rivlin
    TI__Mastermind 43875 points

    Micheal,

    Please have a look at this forum thread which is also talking about the same issue.

    http://e2e.ti.com/support/data_converters/videoconverters/f/376/p/259732/924349.aspx#924349

    Basically, there is no way to measure the exact pixel rate and it is necessary to basically 'guess' based on the horizontal and vertical timing measurements what you 'think' the resolution is, hence what the pixels per line etc... is.

    This is a limitation of analog VGA which does not send either a data valid nor a pixel clock with the video.

    VESA specifies various resolutions and timings and it is necessary to use these as guides to 'best guess'

    Thankfully most 'standard' resolutions are unique enough in horizontal and vertical frequencies such that the 'guess' is accurate.

    BR,

    Steve