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640x480 @ 60Hz with 100MHz? — Parallax Forums

640x480 @ 60Hz with 100MHz?

RaymanRayman Posts: 14,826
edited 2009-02-21 13:58 in Propeller 1
Probably not too many of us with 100 MHz oscillators or 6.25 MHz crystals, but...

The spec for standard vga is 25.175 MHz, which is very close to 25 MHz, matching the 25 MIPS of one cog run at 100 MHz...

So, I'm contemplating trying to drive the VGA port at this standard frequency.· Anybody think it's possible (or impossible)?

Assuming the video PLL can be in sync with the Prop clock, the Prop could also directly generate a dot clock signal that can be sent to a HDMI chip...



Post Edited (Rayman) : 2/20/2009 2:19:06 AM GMT

Comments

  • potatoheadpotatohead Posts: 10,261
    edited 2009-02-20 01:33
    Not enough instructions for a loop.

    Gotta divide MIPS by the number of instructions required. This means multiple COG's. What else will the propeller be doing, and since RAM is 32K, what is the display purpose?

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  • Mike HuseltonMike Huselton Posts: 746
    edited 2009-02-20 01:36
    Looks like a job for the SixBlade Prop...lotsa video ram.

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  • RaymanRayman Posts: 14,826
    edited 2009-02-20 01:37
    Ok, so I guess I still need Waitvid... But, perhaps the dot clock could be made a stable 25 MHz.

    If it did work, then one can add a chip and have HDMI out... I saw a very cool, tiny projector at Digikey today...
  • Mike HuseltonMike Huselton Posts: 746
    edited 2009-02-20 01:40
    I saw that, too. Pico Projector by Texas Instruments - $349.00

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    Post Edited (James Michael Huselton) : 2/20/2009 1:46:06 AM GMT
  • Mike GreenMike Green Posts: 23,101
    edited 2009-02-20 01:43
    How do you plan to do this? You have only one instruction time per pixel. You'd have to have a MOV OUTA,... followed by 3 SHR OUTA,#8. There's no time for a jump, so you'd have to execute linear code and there's way less than 640 instructions per cog.
  • Mike HuseltonMike Huselton Posts: 746
    edited 2009-02-20 02:01
    Hmm...that seems to be a conumdrum alright. I was speaking intuitively, and not taking time to work through the the math, Mike.

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    Post Edited (James Michael Huselton) : 2/20/2009 2:07:47 AM GMT
  • RaymanRayman Posts: 14,826
    edited 2009-02-20 02:14
    Ok, Ok, we definitely need Waitvid...· I'll change my first post...

    I think it could work with 4 cogs, but probably don't want that...

    I want to try HDMI output, but I'm not sure how forgiving HDMI/DVI monitors are with the timing...


    Post Edited (Rayman) : 2/20/2009 2:25:45 AM GMT
  • BaggersBaggers Posts: 3,019
    edited 2009-02-20 14:23
    Rayman, are you wanting to do 32 pixels per waitvid? or 4 or 8 or 16? don't forget this will give you a little more freedom in getting your bits to the waitvid instruction [noparse];)[/noparse]

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  • RaymanRayman Posts: 14,826
    edited 2009-02-20 17:03
    Maybe I don't need 100MHz clock...

    Just tested "Vga_hires_text_demo" with 640x480 and pixel rate = 25 MHz and my monitor synced at 57.7 Hz vertical...

    Maybe that's close enough.·

    I think I'll make a little test board for the TFP410.· Just need to generate a pixel clock output somehow...· Maybe using ctrb or another cog...
  • BaggersBaggers Posts: 3,019
    edited 2009-02-20 18:27
    yeah good idea for pixel clock too [noparse];)[/noparse]

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  • Cole LoganCole Logan Posts: 196
    edited 2009-02-20 18:38
    If you or anybody could get the pixal clock figured out it would open a lot of doors to use TFT screens.
  • Cluso99Cluso99 Posts: 18,069
    edited 2009-02-21 13:58
    There was a recent thread about using the counter for high speed comms - shifting bits in and out. Maybe there is something useful in that thread you could use, together with multiple synchronised cogs.

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