The Mega Game Gear. A Sega Game Gear cart for the Genesis/Mega Drive. Is it possible?

So I was talking to a guy on YouTube and an idea sprung into my head. Is it possible to make a GG cart similar to the Super Game Boy? I know the Genesis /Mega Drive only supports the Master System's video mode 4 and I heard it doesn't support the video mode needed for GG games but could that be fixed or would the color palette issue still be there? Is this "Mega Game Gear" really possible, or is it completely unnecessary with Tim Worthington's GGTV board out there and an HDMI mod on the way?

I was wondering if the Genesis/Mega Drive could be used in a way that both Master System mode and Genesis/MD mode were enabled so the MGG could use the Genesis/MD for video (including color palettes) and Master System mode for everything else. Is that possible or am I just insane (most likely)? Would it just be easier to do something like the SGB that has the actual GG hardware on it and uses the Genesis/MD for controller, power, and A/V output?

 

I am also quite interested in this situation. My interest stems from wanting a consolized Game Gear, but having no more space on the shelf. Petty...I know, but here's what I've thought of and learned so far.

I don't believe it is possible to "fix" the color palette or video mode issues with the existing hardware. With my limited understanding of the Genesis VDP, both issues are one in the same and result of missing functionality that could not be added without a VDP replacement. Maybe someone like Tim Worthington could recreate (or in someway intercept) the VDP in the Genesis with the missing video modes from the Game Gear...maybe not. Even if you did, you'd have a button mapping problem. The Game Gear has a "Start" button that the Master System doesn't, and therefore the Start button would be inaccessible with the Genesis in Master System mode without additional (potentially impractical/impossible) hackery. Another problem is that you couldn't have a 32x installed, as the the 32x blocks Master System mode.

This statement is largely incomprehensible to me. The Game Gear games would run completely in Master System mode if not for the lack of palette selection and button mapping problems. This is why it is relatively easy for a experienced ROM hacker to make conversions for Game Gear games to the Master System.

I am seriously considering trying this later this year. I have a GGTV board from Tim Worthington sitting on my desk just waiting to get used. As my goal is to somehow incorporate the Game Gear hardware into my existing Genesis/Sega CD/32x, I was thinking that it could be placed in the free space to the left of the motherboard in the Sega CD model 2 I have. To do this, I would have to figure out how to:

• Demux the Genesis controller port and get these signals to the Game Gear motherboard - (some 74x logic chips should be able to do this pretty easy)
• Inject A/V/RGB into the chain - (maybe like the 32x does)
• Add more 9 volt power - (either tap off of the Sega CD or add another power supply)

Anyone have anything to add here?

 

Game Gear also uses video mode 4, the only difference is that it has a larger color palette (wider CRAM) and specific hardware registers that GG games use to check for START button, do stereo panning on the PSG sound chip channels, communicate with the link cable, check the console region, etc. This hardware does not exist on anything but a Game Gear, hence why you got incompatibilty issues when running Game Gear games on a Mega Drive and it can not be "fixed" other than by using Game gear hardware.

It's not possible because both modes are exclusive, inside the MD, chips use the M3 pin to switch between the two modes and this can not be "hacked" since it's internal to the chips.
Also, even if it was possible, it wouldn't magically fix GG games because MD mode is still limited to a smaller color palette than what the Game Gear is using (9-bit vs 12-bit) and GG specific hardware registers are still not there.

This is not possible either because you can not pass video signals or read controllers through the cartridge port, it's not designed for that and the reason why the 32x needed mixing cable.