80 Column Card for C64 & possible to use as C128 3rd desktop

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Miro

My ColourPET project relies on the fact that the PET already has two 1K banks that can be re-configured making one bank into colour. It's only 40 column at the moment, but I am working on an 80-column version. It could be adapted as a cart for C64 or VIC-20 but you would need to provide the ram and recreate the other misc circuitry. I'm currently designing ColourPET+G (about 90% complete) and making PCB's, which is quite fun.



The C128's VDC has the advantage that all the support circuitry is built into the VDC chip, plus it has been expanded to support graphics. Really all you need are the VDC, ram, xtal, and a couple ttl chips for decoding. The nice thing (which is also a bad thing) about the VDC is the video ram does not take up space in your memory map, which means it can be added without interfering with existing system ram. Getting VDC chips, however, will be the hard part.



If you can't get a VDC chip and you don't care what chip you use then I would suggest using a Yamaha V9958. It's used in MSX computers and is still readily available on ebay for reasonable prices. It outputs RGB so can be used on 1084-type monitors. This chip, in my opinion, is much more powerful than the VDC chip, has more colours, sprites, and special hardware graphics commands. It won't be easy to program but it can be implemented with minimal parts as well. MSX schematics are on the web and could easily be adapted to 6502 architecture. Actually, there is a 6502 based game system called the CreatiVision that uses the original TI variant of this chip, so you can see how it's done.



I have actually started designing my own V9958-based cart, but it's only in the preliminary stages. I'm using Kicad and have created a V9958 chip for the parts library, and have the RAM circuitry finished. What's left are the cartridge interface, RGB output, and eprom firmware sections.



Steve

Thanks for the info Steve.

Have you considered a project for the C128? :-)

Great! Good work Miro. I will keep a lookout.