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Export VGA pixel clock — Parallax Forums

Export VGA pixel clock

nutsonnutson Posts: 242
edited 2009-06-09 16:16 in Propeller 1
I want to·slave an FPGA (generating·graphics) to a propeller (generating text) and need to bring out the VGA pixelclock for that. Countermode "PLL internal" however does not allow an A or B pin to be set (correct?). Current plan is·to·modify·the VGA driver to·setup the second counter eaxtly as the first one, and bring that one out on a pin. Any other suggestions?

Nico Hattink····

Comments

  • MagIO2MagIO2 Posts: 2,243
    edited 2009-06-09 11:40
    You don't have to use PLL internal, you can use any of the PLL modes to run the video-generator. So, use PLL single-ended and you have a running video-generator and you have the clock at a pin.
  • nutsonnutson Posts: 242
    edited 2009-06-09 11:46
    Thats what I wanted to know, thanks
  • kuronekokuroneko Posts: 3,623
    edited 2009-06-09 12:02
    MagIO2 said...
    You don't have to use PLL internal, you can use any of the PLL modes to run the video-generator. So, use PLL single-ended and you have a running video-generator and you have the clock at a pin.
    Are you sure about that? If so, why is there a dedicated PLL mode for video? Or is that one just like the other PLL modes without using a pin (i.e. no pin/A/A+B)? The documentation makes it sound like it's the only mode you can use for video.

    Post Edited (kuroneko) : 6/9/2009 12:20:35 PM GMT
  • MagIO2MagIO2 Posts: 2,243
    edited 2009-06-09 12:33
    Pretty sure, I used the video genarator to shift out values into a connected shift register. So I needed the video generator clock as well ... and it worked.

    I guess what they wanted to point out in the manual is that internal mode only is useful in case you run the video generator with it. But in opposite to the other two PLL modes you safe the pin(s).

    Post Edited (MagIO2) : 6/9/2009 12:38:54 PM GMT
  • kuronekokuroneko Posts: 3,623
    edited 2009-06-09 12:39
    Thanks. I remember that you played around with the video shifter so that kind of suggested you know for sure [noparse]:)[/noparse]
  • RaymanRayman Posts: 14,833
    edited 2009-06-09 13:04
    Is this true? That's the missing ingredient for the HDMI output setup I was looking into... I kinda gave up when I didn't see an easy way of generating the pixel clock...

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  • BeanBean Posts: 8,129
    edited 2009-06-09 13:15
    Oh yeah ! HDMI would be very cool.
    How close are you to generating HDMI ?

    Bean.

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  • RaymanRayman Posts: 14,833
    edited 2009-06-09 14:19
    Well, I've a a TFP410 sample for a while now, but haven't found the time to make a board for it yet. I could be very wrong, but I think it would be quite simple to adapt the VGA drivers to generate HDMI with this chip. The only thing that wasn't very clear to me was how to generate the pixel clock. But, if MagIO2 is right, that's pretty simple too....

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  • nutsonnutson Posts: 242
    edited 2009-06-09 14:49
    I can confirm that MagIO2 is right, just ran the VGA_1024_768_tile_driver demo and modified the counter mode setting in the driver from

    MOVI CTRA,#%00001_110 "PLL internal mode"

    into

    MOVI CTRA,#%00010_110 "PLL single ended"

    and it works fine
  • Bill HenningBill Henning Posts: 6,445
    edited 2009-06-09 16:03
    Good news!

    Now if we could only get the pixel clock to only output during active pixels without using external logic...
    nutson said...
    I can confirm that MagIO2 is right, just ran the VGA_1024_768_tile_driver demo and modified the counter mode setting in the driver from


    MOVI CTRA,#%00001_110 "PLL internal mode"



    into



    MOVI CTRA,#%00010_110 "PLL single ended"



    and it works fine
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  • RaymanRayman Posts: 14,833
    edited 2009-06-09 16:16
    I think the TFP410 can be programmed via I2C to automatically generate an internal DE (data enable) signal so that the dot clock can be continuous. Or, another Prop pin could be used as the DE signal...

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