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Forum Neo Geo Pocket Color Video Out (DAC/FPGA)
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  • retro gaming
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Related

Neo Geo Pocket Color Video Out (DAC/FPGA)

kragit
kragit over 8 years ago

Hi everyone!

 

Looking to achieve RGB analog video out on a Neo Geo Pocket Color. No known mods currently exist for this. There are single digit K2_VIDEOs out in the wild that achieve this, but I believe these were made by SNK themselves for internal use only. Other people have apparently gotten video out with FPGAs, but no one has publicly documented it.

 

Here are the LCD signals as printed on the board & additional information from someone who's apparently achieved this:

 

I've done it with a small FPGA. The LCD signals can't be simpler: R0~3 is 4bit red, G0~3 is 4bit green, B0~3 is 4bit blue, DOTCLK is the pixel clock, SPL is horizontal sync, SPS is frame sync.
[...]
It can't be done by just wiring a scart cable to the board, you have to buffer and convert the color data from the NGPC, then do digital to analog conversion if you want analog RGB output.

 

I'm venturing into the FPGA scene for this with no past experience with FPGAs and a rudimentary understanding of digital electronics (I can follow guides, solder, etc. I built a CMVS this way).

 

Any help would be appreciated. Thanks!

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Top Replies

  • johnbeetem
    johnbeetem over 8 years ago in reply to kragit +4 suggested
    Adam Kragt wrote: Appreciate the info! The biggest thing is just trying to figure out where to start as a total beginner. With FPGAs, start by copying a tutorial design exactly. FPGA tools have a steep…
  • jc2048
    jc2048 over 8 years ago +3 suggested
    You might consider applying for this roadtest https://www.element14.com/community/roadTests/1796/l/Terasic-P0082-DE0-Nano-FPGA-Development-Kit That would get you some kit to use and an opportunity to learn…
  • johnbeetem
    johnbeetem over 8 years ago +3 suggested
    These are general comments about FPGAs and VGA output and probably not all that helpful for the NPGC, but here goes anyway. There are a number of FPGA boards out there that support VGA graphics, and some…
  • jc2048
    0 jc2048 over 8 years ago in reply to Jan Cumps

    Very good. The HSYNCs look overly wide to me and there's no blanking at the end of the line, but you can fiddle around with all that once you see it on the screen. What next? Asteroids in VHDL would be impressive!

     

    And it's a chance to show off your new scope. Which model is it? Should I be envious?

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  • Jan Cumps
    0 Jan Cumps over 8 years ago in reply to jc2048
    The HSYNCs look overly wide to me and there's no blanking at the end of the line

    I'll have to read-up on the VGA signal, but I believe there should be blanking.

    From the Xess doco:

    image

     

    And it's a chance to show off your new scope. Which model is it? Should I be envious?

    Yay Tektronix  TBS2102TBS2102 100 MHz 2 channel Yes please

     

     

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  • Jan Cumps
    0 Jan Cumps over 8 years ago in reply to jc2048

    Jon Clift wrote:

     

    ... there's no blanking at the end of the line ...

    Yes, I'll have to recheck the design:

    image

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  • Jan Cumps
    0 Jan Cumps over 8 years ago in reply to Jan Cumps

    I have now loaded a real image to RAM, and it looks ok now (edit: no I see the blackout for vsync but not yet for hsync end)

     

    Yellow: horizontal sync

    Blue: vertical sync

    Magenta: one of the video signals

     

    The capture below is triggered on the vertical sync, and shows blanking before and after.

    image

     

    This one shows the same signals, zoomed out to show multiple vsyncs:

    image

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  • jc2048
    0 jc2048 over 8 years ago in reply to Jan Cumps

    From the scope timing it looks like 600 displayed lines and a framerate of 70Hz. (Presumably, there are going to be 800 pixels across the line.)

     

    That doesn't tie up with the documentation you showed above which was a 480 line 60Hz mode.

     

    Have you found a VGA cable yet? I won't believe it until I see it.

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  • Jan Cumps
    0 Jan Cumps over 8 years ago in reply to jc2048

    I'm going to buy a cable on the second hand market in Brussels Marollen this Sunday.

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  • Jan Cumps
    0 Jan Cumps over 8 years ago in reply to jc2048

    ... Yes, all samples are 800 x 600

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  • Jan Cumps
    0 Jan Cumps over 8 years ago in reply to jc2048

    ahead of plan image

    image

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  • Jan Cumps
    0 Jan Cumps over 8 years ago in reply to Jan Cumps

    ... and then it turns out that my brand new flashy tv doesn't have VGA image

    I have a HDVD HDMI  -> VGA converter but it doesn't work the other way. Darn...

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