MottZilla wrote:
For today it's not a big deal to equip a cartridge with alot of ROM. You could easily have a mapper that can use the internal nametables or pick out of something like a 16 megabit (2 megabyte) EPROM giving you plenty of space
But how many address bits in each mapper register? A typical 8-bit register can address only 256 different nametables. If you plan to make your mapper on a CPLD, each latch costs you money. I've been told 5.0 V CPLDs with more than 36 latches get more expensive.
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and unlike mapper 68 you could have separate CHR-ROM and NameTable ROMs.
Actually mapper 68 boards usually have their CHR ROM divided into two chips, and nametable data can come only from the chip corresponding to the second half of memory.
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Someone made something like a FMV awhile ago that just used CNROM's abailty to have some huge amount of CHR-ROM.
CNROM proper is limited to 32 KiB. Clone boards topped out at 64 or 128 KiB because a 74161 was cheaper than a 74377, which is what emulators are supposed to emulate if CHR ROM is bigger than 32 KiB.