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PostPosted: Sun Apr 16, 2006 2:41 pm 
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As a fun project I want to create a device+software to download NES cartridges via a parallel port so they can be played on an emulator.
I thought this would be a good way for me to learn some low level hardware stuff and get to play video games at the end :)

Someone suggested I start with an unbaked cartridge like Super Mario Bros., which I think is a good idea, but ....

1) After looking at the cartridge schematic there seems to only be 13 address lines for each the PRG and CHR, I dont see how I can address every byte of memory

2) What addresses do I iterate over to download the PRG rom? What addresses do I iterate over to download the CHR rom? Do I use the cpu memory mappings, or do I start from $0000 on each address bus?

3) I eventually want to be able to download mmc1 games, but I only understand the absolute basics of paging, I am having the darndest time understaning how that pager works :( So if someone could give me a primer in very basic language I would really appreciate it.

thanks!


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PostPosted: Sun Apr 16, 2006 7:35 pm 
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fps_gamer_ wrote:
As a fun project I want to create a device+software to download NES cartridges via a parallel port so they can be played on an emulator.

THis is called a "dumper". Having an easily available dumper would bring NES emulation into solidly-legal territory at least in the United States.

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1) After looking at the cartridge schematic there seems to only be 13 address lines for each the PRG and CHR, I dont see how I can address every byte of memory

There are 15 lines for PRG (A14-A0), plus one with the A15 signal multiplexed with the clock. You must have missed something on the schematic.

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2) What addresses do I iterate over to download the PRG rom?

$8000 to $FFFF on the CPU bus, making sure to have the chip select lines in the proper state.

Quote:
What addresses do I iterate over to download the CHR rom?

$0000 to $1FFF on the PPU bus, making sure to have the chip select lines in the proper state.

Quote:
3) I eventually want to be able to download mmc1 games, but I only understand the absolute basics of paging, I am having the darndest time understaning how that pager works :( So if someone could give me a primer in very basic language I would really appreciate it.

A mapper replaces the upper address lines with the content of a register inside the mapper. You might want to understand boards that use discrete logic mappers, such as AOROM, UNROM, CNROM, GNROM, before you tackle S*ROM (MMC1).


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PostPosted: Mon Apr 17, 2006 5:38 pm 
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May I suggest purchasing a CopyNES kit and building it? It does already what you want to do and in the process, you can learn how it works.

Why re-invent the wheel??

As far as addressing memory, read up on how mappers work. They do the "magic" you're after.


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PostPosted: Tue Apr 18, 2006 7:14 am 
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leonk wrote:
Why re-invent the wheel??

Because CopyNES is expensive.


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PostPosted: Tue Apr 18, 2006 11:06 am 
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Why re-invent the wheel??


Re-inventing the wheel is underrated. How else will you learn the things that the original inventor learned while inventing it?


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PostPosted: Tue Apr 18, 2006 11:24 am 
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I agree with blargg

I mean when you look at the nesdev community as a whole -- pretty much everyone here has been reinventing the same wheel for years.


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