Derivavision - a Creativision clone

Discuss the CreatiVision hardware: models, revisions, fixing, hacking and modding.
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leadedsolder
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Derivavision - a Creativision clone

Post by leadedsolder » Sun May 28, 2023 5:36 pm

Hi again everyone,

You might remember me from the introduction thread I made last month. This is going to be the project thread for my Creativision clone build, which I've chosen to call the "Derivavision."

I will also be tracking the development in more (some would say too much) detail on the Leaded Solder blog – probably the first blog post on this will be early July as I tend to procrastinate on editing.

Here's the constraints I've set out for myself at the moment:
  • NTSC TMS9918A for the VDP, since I have a lot of them and I live in Canada;
  • Composite output, no RF;
  • Plays retail cartridges;
  • Single-voltage USB power supply (with optional connector to inject other voltages if the cartridges/tape interface needs them;)
  • No controllers or keyboard yet because I don't quite understand the matrix;
  • Open-source everything as soon as it starts to work.
I'll lead off with some exciting news.

As of about ten minutes ago, after some debugging and bodge-wiring, the Derivavision has run through a couple cycles of the attract mode of Sonic Invaders (see below.) Thank you very much to Cheshire Noir for providing me with a copy of the game, as otherwise I'd still be hunting eBay for one.

Please don't mind the awful colours; the green gun on my test PVM has essentially died at this point. As you can see from the stickers on the front, this thing has seen tens of thousands of hours in broadcast television.

So far the bodge list is relatively minimal, although I am noticing that the video output on this system is much worse than on my Sega SG-1000 clone or ColecoVision clone despite having "sort of" the same output circuit. Cleaning up the luminance ringing and some other colour issues will be worked out in the next few weeks (I ran out of ferrite beads so things are sort of jumpered-together; I think the jumper is causing interference issues.)

Please check out the GitHub repository here, although I don't recommend you actually build one for yourself yet, at least not until the keyboard/controller interface is figured out. The attract mode on Sonic Invaders isn't that much fun to watch.

Thanks everybody! I will update this thread as more progress is made.
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Scouter3d
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Re: Derivavision - a Creativision clone

Post by Scouter3d » Sun May 28, 2023 6:14 pm

Wow! Simply amazing! Cheers, TOM:0)
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Mobsie
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Re: Derivavision - a Creativision clone

Post by Mobsie » Sun May 28, 2023 8:16 pm

Yeah 👍👍 this is what i have waiting for.
How much must one change to use the pal TMS?

Cheers
Mike
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leadedsolder
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Re: Derivavision - a Creativision clone

Post by leadedsolder » Mon May 29, 2023 1:15 am

Mobsie wrote:
Sun May 28, 2023 8:16 pm
Yeah 👍👍 this is what i have waiting for.
How much must one change to use the pal TMS?

Cheers
Mike
Thanks!

Not much has to change, although I haven’t tried it. It would be a new board - the TMS9928 (NTSC) and TMS9929 (PAL) outputs in YCbCr component colour instead of composite video like the TMS9918 I’m using does.

So you’d need to devise some kind of mixing circuit to produce PAL composite output, or even 15kHz RGB + CSync. I would suspect you could “borrow” the original output circuit from a CBS ColecoVision or a PAL Creativision and add an amplifier to make viable PAL composite output. There might even be an example circuit in the data sheet for the 99xx series.

You would also need to change the crystal for the VDP as I think the 10.7… MHz is specific to NTSC colour burst.
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cheshirenoir
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Re: Derivavision - a Creativision clone

Post by cheshirenoir » Mon May 29, 2023 4:30 am

Amazing work there!

The controllers took me ages to understand, and I'm still not 100% sure I know what's really going on.

John
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Mobsie
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Re: Derivavision - a Creativision clone

Post by Mobsie » Mon May 29, 2023 10:24 am

Great, Sorry for asking so much. But i am to lazy to check your diagram. You use one if the TMS RAM mods to not need these strange old ram and voltage?
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Mobsie
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Re: Derivavision - a Creativision clone

Post by Mobsie » Mon May 29, 2023 10:25 am

And please make a photo from the top of the board please.

Thank you 🙏
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leadedsolder
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Re: Derivavision - a Creativision clone

Post by leadedsolder » Mon May 29, 2023 2:19 pm

Mobsie wrote:
Mon May 29, 2023 10:24 am
Great, Sorry for asking so much. But i am to lazy to check your diagram. You use one if the TMS RAM mods to not need these strange old ram and voltage?
It is modified to use static RAM, yeah. You could find 5v 1-bit DRAM as well but I didn’t have any on hand when I started designing my ColecoVision clone and I’m not sure how long China’s supply will hold out.

I’ll put up a board pic later today!
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leadedsolder
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Re: Derivavision - a Creativision clone

Post by leadedsolder » Mon May 29, 2023 4:05 pm

Here's a picture of the board, as promised. There's a single bodge wire on the underside that should be cleaned up on the next revision (I accidentally tied the TMS9918 MODE address pin to A14 instead of A0... a little off.)

Not everything is populated at the moment because I'm waiting on the aforementioned ferrites and haven't thought too hard about the tape interface yet.

The keyboard connector is meant to go at J1 and J2, but I also don't have the female connectors on hand for that yet to start prototyping the keyboard (they're in the mail.)
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Mobsie
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Re: Derivavision - a Creativision clone

Post by Mobsie » Mon May 29, 2023 6:53 pm

Thank you 👍👍👍
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