My lockdown project has been hacking up my CFX-9850G calculator. So far I have physically removed the ROM of the calculator and replaced it with a new ROM (I wa

My lockdown project has been hacking up my CFX-9850G calculator. So far I have physically removed the ROM of the calculator and replaced it with a new ROM (I was able to get old-stock chips from aliexpress) flashed with a patched version of the original OS that includes a new BASIC command to jump to a fixed location in RAM and start executing whatever is there. This means I can write and run arbitrary machine code in the calculator’s RAM by abusing the built in backup feature. The Hitachi CPU in the calculator is quite strange but by working with the little information I can find online [1] I have written an assembler and linker for creating compatible machine code from a custom assembly language. The resulting code runs much faster than in BASIC because it doesn’t have to be interpreted. Here [2] is a video of the calculator jumping into RAM and running a Game of Life program that I wrote when Conway died. I’m currently writing code to run the 3-colour display for a replacement Forth-like shell/OS with the aim to eventually get to the point where I can replace the calculator ROM completely with my own. Writing my own mathematical functions for a calculator is fun when (AFAIK) the CPU itself lacks even multiplication opcodes. [1] http://martin.poupe.org/casio/ http://martin.poupe.org/casio/ [2] https://youtu.be/cTB5YM898g4 https://youtu.be/cTB5YM898g4