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PostPosted: Sat Jul 27, 2019 6:12 am 
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Hi everyone ... I wanted to know if I can update this old cartridge for Famicom from eprom 27c256 to Eprom 27c512 in order to put more interesting games.
Best Regards to all !


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PostPosted: Sat Jul 27, 2019 6:49 am 
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My educated guess is that your board implements CNROM (iNES mapper 3), with the '161 controlling which 8 KiB bank of CHR ROM is visible. With only trace cuts and rewires, in theory you could upgrade it to a subset of GNROM, Color Dreams, or BA-JOGGING.

GNROM (#66)
Licensed commercial GNROM games use a 128 KiB PRG ROM and a 32 KiB CHR ROM. The PRG ROM is too large to fit in your 27C512. The cost-reduced MHROM would support Super Mario Bros./Duck Hunt but that's it.

BA-JOGGING (#3)
Bandai made an oversize variant of the CNROM board that supports up to 128 KiB CHR ROM. It was used for Family Trainer 4: Jogging Race, but that has 128 KiB CHR ROM. A functionally compatible board was also used for Panesian's porn games, but I don't know how big their CHR ROM is.

Color Dreams (#11)
A lot of games by Color Dreams use PRG ROM and CHR ROM no bigger than 64 KiB. Games after it pivoted to Wisdom Tree (other than Bible Adventures) use 128 KiB ROM.

BNROM (#34) or AMROM (#7)
The vast majority of BNROM games are 128 KiB (Deadly Towers) or bigger (Lizard; Haunted: Halloween '85). But if you have a 6264 or compatible SRAM, you can rewire the CHR side to take that and then route the D0 output of the '161 to PRG ROM A15. This would give you 240p Test Suite and maybe one revision of RC Pro-Am if it doesn't rely on ANROM's bus conflict avoidance.


EDIT: Avoid loaded word "clone" for Panesian products

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PostPosted: Sat Jul 27, 2019 7:00 am 
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Ok ... can I write CNROM about these 27C256 games like Kick Master?


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PostPosted: Sat Jul 27, 2019 7:15 am 
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Location: NE Indiana, USA (NTSC)
A 27C512 can hold up to 524288 bits or 512 kilobits. Because there are 8 bits in a byte, this equates to 65536 bytes or 64 KiB. To go bigger than that, you need a 27C010, which is 1 megabit or 128 KiB, or a 27C020, which is 2 megabits or 256 KiB.

According to its entry on NesCartDB, Taito's Kick Master has a 128 KiB PRG ROM, a 128 KiB CHR ROM, and an MMC3 mapper. It will not fit on your board or your memory. If you absolutely have to use up a large supply of recycled or new-old-stock 27C512s to reproduce Kick Master: You will need four of them, two for PRG and two for CHR, and a circuit to select one of them depending on the MMC3's PRG A16 and CHR A16 outputs. You will need a custom circuit board with an MMC3 (or a clone such as AX5202P) and four ROM sockets. I don't recommend this route.

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PostPosted: Tue Jul 30, 2019 5:49 am 
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tepples wrote:
A clone of this board was also used for Panesian's porn games, but I don't know how big their CHR ROM is.
64 KiB, and it's not a clone, as it also supports 64 KiB PRG-ROM.


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