jm + gameboy   1

How the Game Genie worked
"Sometimes it was really easy to find cheats, because the code was very straightforward, and sometimes it was a massive pain in the arse," recalls Jon. "In simple terms, if a game started you with three lives I'd set up the logic analyser to stop when it found the value three being written to RAM. Then I'd use the Game Genie to change that 3 to say a 5, reboot the game and see if I started with 5 lives. If not, then I'd let it find the next time it wrote 3 into RAM and try that.

"Infinite lives codes were always the best. Once I'd found where in RAM the lives value was stored I'd then monitor when it got decremented. What I was looking for was where the game's original coder used -most likely - the DEC A (&H3D) instruction after reading the lives value from RAM, and then storing it back into RAM. If I found this then all I had to do was swap out the DEC A (&H3D) decrement operation with a NOP (&H00), which performed no operation. So the lives value would be left as-is and voila the player had infinite lives."
games  gameboy  game-genie  via:its  logic-analysers  reverse-engineering  history  hacking 
12 days ago by jm

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