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8

To my knowledge, the NES and the Famicom had the exact same CPU (a Ricoh 2A03). So, it's unlikely there were any differences in behavior between the two with regards to undocumented opcodes. As the Ricoh had a 6502 core, you could also expect it has the same undocumented opcodes as the 6502 (not your question, though) - And this document seems to confirm ...


6

What is the lowest available to the cartridge CPU address, i.e. how much down to zero the cartridge space may span, whether it would be PRG-ROM, PRG-RAM or cartridge registers? Well, everything up to 4020 is filled, or better internal chip select decoding will fire for each and every address. For example the 2 KiB internal RAM are visible 4 times on $0000, $...


5

I'll assume you only want to modify small parts of the game, rather than the entire game. (If you wanted to modify the entire game, you'd just make a new cartridge holding the entire image.) Your objective: replace some but not all of the words* of the game with a new set, leaving the majority of the game unchanged. (* as in addressable data units, not ...


5

So I was wondering what happen if battery run out. Do you lose your save games? In an unplugged/stored cardridge yes. After all, they are RAM based. Now, if it's still pluged and powered, then usualy not. Ofc. it depends how it's wired. With standard circuitry that's also the way to change batteries before they go dead.


4

Many cart-based games used battery-backed SRAM for storing saved game state. The RAM was usually powered by a lithium coin cell that could keep the RAM contents powered for a number of years. Once the battery died, the cartridge lost the ability to store game save data. While the cart was plugged in, the console would power the SRAM so the game would ...


3

The two disk systems' technology were completely different. The Famicom's disk system used a magnetic-storage floppy disk, which (according to Wikipedia) had a total capacity of 112 kilobytes (56kB per side). These were also known as Super Disks. Even when launched in 1986, this was relatively small: since 1984 IBM's PC-AT could store 1.2MB on a 5 1/4" ...


3

The cartridge can map anything anywhere, however there's restrictions if it overlaps existing hardware in the console. Write-only registers could be mapped in a way that overlaps RAM in $0000-$1fff range. Read-only registers could be mapped overlapping $2000, $2001, $2003, $2005 and $2006 PPU registers (or any of their mirrors), as well as $4000-$4014 pAPU ...


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