Mega tic-tac-toe is, like the name implies, a 2-player tic-tac-toe game running on the Sega mega drive.

I was still working on Demon District when I started this project. The reason I did so was because I grew somewhat bored of programming 6502 assembly language.
I didn’t stop working on Demon District but felt like I needed more of a challenge on the side.

So I decided to tackle another console I wanted to program for for a long time.
The Sega Mega drive!

The Mega drive uses the Motorola 68000 CPU, which is quite a bit more powerful than the 6502 inside the NES, but with great power comes great responsibility. It took some real getting used to dealing with data lengths (bytes, words and longs) and the various beginner traps such as the impossibility to read a word or long from an odd address.

The vdp (video display processor) also proved to be more of a challenge compared to the ppu inside the NES. For starters the vdp does not have a fixed memory map like the ppu. This is very useful as it gives you the freedom to use more v-ram for tile data and less v-ram for screen data or visa versa. This was not too difficult to understand, the difficulty (initially) came from setting up the vdp properly not helped by the fact that the vdp tended to show a black screen whenever I made a small mistake, like writing to a non-existent register.
One other big advantage the vdp has over the ppu is the ability to alter v-ram outside of v-blank, compared to the ppu where you have to absolutely make sure you only wrote to v-ram during v-blank else the image would glitch.

Overall, for a small side project I’m quite happy with the result. I learned quite a lot and threw some fun challenges my way.

Disclaimer:
Even though the tile screen says game of the year edition it never received that title, it’s just a joke. 😛