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Intellivision ntsc rgb mod design help

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#1 emerson OFFLINE  

emerson

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Posted Wed Nov 7, 2018 8:16 AM

I was looking into rgb mods for the intellivision and besides the RetroRGB mod kit there isn't much available for ntsc models. I discovered a pal mod circuit here which requires 3 bits for red, green and blue, which ntsc models don't have. Instead, ntsc models have a 4bit code (one nibble for each background color) and the AY-3-8915 does all the color processing. My goal is to design a decoder circuit which takes the 4bit color code and convert it into the 3 bits per color rgb code. To do this I need to know the 3bit rgb codes for each background color so I can design the decoder.

 

Does anyone have a pal intellivision service manual with the rgb color table?

 

Would someone with a pal intellivision be willing to open it up and measure the rgb bits on the LM1886 for each background color? I have included a test rom and truth table for anyone willing to help me out.

 

Thank you!

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#2 mr_me OFFLINE  

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Posted Fri Nov 9, 2018 3:57 PM

I don't have a pal intellivision but I wonder how accurate that digital rgb data might be. I only say this because that digital rgb goes through an analog pal conversion, which looks different than an ntsc intellivision.

Maybe you've seen this, but there is an internal mattel document that has the yiq colour information sent to their hong kong manufacturer.

http://papaintellivi...42011_00001.pdf

Edited by mr_me, Fri Nov 9, 2018 3:59 PM.


#3 emerson OFFLINE  

emerson

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Posted Sat Nov 10, 2018 8:41 AM

I have not seen that document so thank you posting it! The color code table is in the ntsc service manual, but the yiq table is new information for me. Now to figure out how to use it...

 

I've read that pal and ntsc intellivisions have color differences so I would assume my proposed method would produce the pal color scheme. I want to say dark greens come out brown but I don't remember what else. Maybe the digital rgb codes could be tweaked to help correct this?

 

I came up with a somewhat cumbersome method of guess and check to try and figure out the rgb color codes. What are your thoughts on this approach:

 

- Set my rgb modded crt next to my Commodore 1702

- mod the Solarfox av circuit to handle two outputs or just build two of them

- feed the composite video into both monitors so the 1702 displays the desired color and the rgb modded crt has the necessary sync signals

- assemble the pal rgb DAC and feed the rgb output signals into the modded crt while the input signals are connected to DIP switches

- manually configure the DIP switches and compare the colors between the two monitors



#4 mr_me OFFLINE  

mr_me

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Posted Sun Nov 11, 2018 3:54 AM

That's assuming the digital rgb colours remain consistent after going through the analog pal conversion.

The guess and check method might work better. Whatever you come up with someone will probably disagree with it. The important thing is the colours are distinguishable. E.g. tan vs yellow vs orange; red vs magenta.

I should have posted a link to this discussion.
http://atariage.com/...tte-flag/page-1

Edited by mr_me, Sun Nov 11, 2018 4:22 AM.


#5 emerson OFFLINE  

emerson

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Posted Sun Nov 11, 2018 10:16 AM

Wow, I'm glad you posted that link. I should be able to use one of those palettes as a reference. Once again I thank you.

 

Whatever you come up with someone will probably disagree with it.

 

True that, haha. Plus, it isn't my intent to sell a kit or anything, this is just for a one off arcade cabinet I plan to build in the future. I'll post my findings once I get parts ordered and do some testing.







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