NES RAM upgrade

Discuss hardware-related topics, such as development cartridges, CopyNES, PowerPak, EPROMs, or whatever.

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Fiskbit
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Re: NES RAM upgrade

Post by Fiskbit »

I think you're making a lot of incorrect assumptions here.

$0800-1FFF is not surely safe; it's entirely legal for a game to read from or write to $0800-1FFF in order to access $0000-07FF, and while I don't have any examples, I am sure they exist. Adding RAM in this region could break such games by making the access go to the new RAM, instead. Similarly, games may access anywhere in the region of $2000-3FFF in order to reach the PPU registers at $2000-2007, and while I don't know of any commercial software that does this, I believe this can be used by homebrew software for console type detection, and there are mitigations for PPU hardware bugs that require accessing mirrors.

Elaborating on lidnariq's point about $4018-401F, $4018-401A are normally disabled (open bus) and only enabled using the test pin, but this requires a mod. $401B-401F don't exist; the IRQ functionality at $401C-401F cannot be used and this region is open bus.

Also, as krzysiobal says, you don't need a replacement board for this, just like you don't need a replacement board for NESRGB nor HDNES, which are both much more significant mods. Keeping the original board is cheaper and easier.


But again, I wonder: having more RAM is cool, but what do you intend to use it for? What is your goal? Knowing what you want out of this project would help us identify relevant problems or make useful suggestions.
Last edited by Fiskbit on Fri Apr 23, 2021 12:14 am, edited 1 time in total.
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tokumaru
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Location: Rio de Janeiro - Brazil

Re: NES RAM upgrade

Post by tokumaru »

The main question is: What problem does this solve, that the current standard practice (RAM on the cartridge) doesn't?
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aquasnake
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Re: NES RAM upgrade

Post by aquasnake »

Instead of extending IRAM to 8K, it's better to extend wram through bank technology. In fact, some mappers support 4x wram bank switching (32KB), while mmc5 should be able to support 64KB wram, and some homebrew flash carts or multicarts support 512KB
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aquasnake
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Re: NES RAM upgrade

Post by aquasnake »

sta $200 is equivalent to sta $A00 or sta $1A00
Fortunately, almost all games do not rely on reading and writing data from different mirror addresses to detect hardware (not excluding some games of first party of Nintendo or Rare)

Therefore, if the console is modified, the risk of compatibility is unacceptable
Concurser
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Joined: Fri Mar 06, 2020 12:30 pm

Re: NES RAM upgrade

Post by Concurser »

Just a few thougths on this subject. I am fond of retrocomputing in general, and thought if a extra RAM bank within a special cartdrige could deliver com IO ports, internal storage and extra mapped RAM for the nes environment?

My idea would be to attach a keyboard and develop a minimal command line operating system, with basic functions and maybe BASIC and assembler/debugger enfironment to explore the 65c02 architecture also.

Do you guys know any ongoing idea like this? There are some small retro computing projects like the Agon light, but I was thinking about what could be done reusing a NES console.

I know the famicom computer environment, but it was aimed more towards end users and not as a development environment.
lidnariq
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Joined: Sun Apr 13, 2008 11:12 am

Re: NES RAM upgrade

Post by lidnariq »

One could easily make a cartridge that contained all the extra hardware you'd need to resemble a 1980s microcomputer - UART (8251), parallel port (8255 or whatever), keyboard interface, floppy drive controller (µPD765), extra bankswitched RAM...

The only question is "then what?"
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Individualised
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Joined: Mon Sep 05, 2022 6:46 am

Re: NES RAM upgrade

Post by Individualised »

Concurser wrote: Fri Apr 14, 2023 11:50 am Just a few thougths on this subject. I am fond of retrocomputing in general, and thought if a extra RAM bank within a special cartdrige could deliver com IO ports, internal storage and extra mapped RAM for the nes environment?

My idea would be to attach a keyboard and develop a minimal command line operating system, with basic functions and maybe BASIC and assembler/debugger enfironment to explore the 65c02 architecture also.

Do you guys know any ongoing idea like this? There are some small retro computing projects like the Agon light, but I was thinking about what could be done reusing a NES console.

I know the famicom computer environment, but it was aimed more towards end users and not as a development environment.
NES uses a 6502 clone inside it's 2A03, not 65C02. There are differences.
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forple
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Joined: Sat Dec 30, 2017 2:09 pm

Re: NES RAM upgrade

Post by forple »

Concurser wrote: Fri Apr 14, 2023 11:50 am Do you guys know any ongoing idea like this?
Get a Subor. They actually put the "Computer" in Family Computer. Has DOS, proper parallel and I/O (including the famed printer port), 512K RAM, and some models even have a 3.5" floppy disk drive, if I recall correctly. Also is backwards compatible with pretty much the entire standard NES library (or whatever you can stuff into a 60-pin cartridge)
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