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PostPosted: Thu Feb 01, 2018 10:48 pm 
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The cartridge connector has a signal called "CIRAM /CE" which is the on-NES-motherboard RAM chip select. Cartridges usually connect this to PPU /A13, per the wiki. If a cartridge has its own RAM and a developer does not want to use the on-board RAM, should the cartridge have a pull-up resistor so that this pin is not floating? I looked as some NES schematics which do not show a pull-up on the mainboard, but I do not know if those schematics were "official".


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PostPosted: Fri Feb 02, 2018 1:29 am 
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According to the schematics for InfiniteNesLives four-screen mirroring variation at https://wiki.nesdev.com/w/index.php/UNROM_512, the UNROM-512 disables the internal VRAM/CIRAM by connecting CIRAM /CE to VCC, and thereby using cart VRAM for all pattern, name and attribute tables.

I guess this is one way to do it, but for better details, i hope someone with more knowledge answers you.


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PostPosted: Fri Feb 02, 2018 2:13 am 
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Only very few licensed games released in 72-pin land tied CIRAM/CE to anything other than PPU /A13.

The MMC5-using games drive it.
Gauntlet adds a 2K RAM and a 74'00 to enable either the extra RAM or the 2K inside the console.
Rad Racer 2 adds an 8K RAM and ties CIRAM/CE high.


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PostPosted: Fri Feb 02, 2018 9:29 am 
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Got it. Thank you!


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