Hello all! It's been FOREVER since I've posted something, and normally I just work on my projects and share them only when they're done, but I wanted to reach out about this one while I was working on it. During this whole Pandemic, I made a really impulsive decision and purchased a Mega Play arcade board. Since then, I've partnered with a user over on the Arcade Projects forums to purchase some custom Mega Play Reproduction cartridge PCBs as well, and I've made a repro of Sonic 2, Sonic 1, and Streets of Rage 2, and I've been having a blast with these. However, there are only like 12 games for the Mega Play total, and there are a few that I'd love to work on porting to the Mega Play. Specifically, I REALLY want to port Dr. Robotnik's Mean Bean Machine, and maybe Sonic 3&K (That one will require a custom BIOS as well, since from what I can gather the BIOS only allows for 2 MB roms max). And, you know, it would be very nice to get Sonic 2 XL on a cart to satisfy my own narcissism... My goal is definitely to make these ports close to the original Mega Play games, with working score boards, more arcade-like features, credit systems, etc. The roms seem to be only slightly different so hopefully the work won't take TOO long :D However, with this kind of work, there's gonna be a lot of ground breaking. I've been using the disassemblies of Sonic 1 and 2, plus a diff file I generated comparing the MP roms to the Genesis roms, trying to find out all of the differences and the changes that I need to port a new Genesis game to the Mega Play. I've gotten about 100 differences into Sonic 1 (of about 3000 differences, mostly pointer addresses that got changed around), when I realized that someone might already have some knowledge on the Mega Play board as well, as well as porting games! So really, the intention of this forum post is less to talk about what I'm doing (although I'd be happy to discuss more), and more to see if anyone else has any experience with working with the Mega Play, and potentially any work with porting games to it!
Funny enough, I've been working on a Sonic 1 Mega Play disassembly myself. While it's still early on, I have gotten a few key parts figured out. This for example, is to sort out how many lives the player will get. It's 3 lives per credit, and will roll back to 1 if you try adding a 5th credit. $FFFFFE6A is the amount of credits, and $FFFFFE68 is the difficulty (iirc the difficulty is determined by a switch on the board). While I'm still sorting out the Mega Play's hardware addresses, it's certainly a start.
That's exactly what I need, thanks Iso Kilo! I have a Mega Play board, so I can confirm that the first DIP Switch set determines the credits/coin and the difficulty. I'd love to know what the board checks for to determine what is a valid Mega Play game. Is it just the presence of the second rom on the cart? If so, what instructions are on that little rom? That's the kind if stuff I'm hoping to get answers to ❤️ I'd LOVE to see what you've got so far, or to help in some way c:
