NES Text Passwords: Demo NES ROM

July 15, 2021

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 use Space or - characters where possible. It kinda simulates how spaces were a valid character in Metroid passwords whose bit value of %111111 was 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 the - to make the change more visually interesting and because exclamation points are cool. ! in Kid Icarus has the same bit value as - in Metroid.





  • 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!