In preparation for an upcoming video, I decided to get some experience
with 6502 assembler and NES development. I built a ROM that will take a
24 character password like in Metroid or Kid Icarus and change it to either
- characters where possible. It kinda simulates how spaces
were a valid character in Metroid passwords whose bit value of
the same as
-, but had the additional behavior of setting the prior
character’s lower bits to on.
Download the ROM here and try it out
in you own emulator!
In the example ROM, I use the exclamation point
! character instead of
- to make the change more visually interesting and because
exclamation points are cool.
! in Kid Icarus has the same bit value as
- in Metroid.
- I used 8bitworkshop’s IDE to write the code and build the ROM.
- I learned the basics of 6502 assembler from Easy 6502.
- I used these two 6502 opcode references to know how to make the CPU do things:
- I used the PPU reference on the NESDev Wiki to understand the PPU enough to make the demo.
- 2021-07-15: Initial post.
- 2021-07-16: ROM updated to better support Nestopia. It didn’t like the palette definition for some reason. Thanks Tyrel!