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Famicom Super Mario Bros / Tennis cart swap trick
http://forums.nesdev.com/viewtopic.php?f=2&t=8988
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Author:  zeroone [ Wed Jan 18, 2017 7:26 pm ]
Post subject:  Re: Famicom Super Mario Bros / Tennis cart swap trick

The other hack also works:

Image

Author:  Pokun [ Thu Jan 19, 2017 4:36 am ]
Post subject:  Re: Famicom Super Mario Bros / Tennis cart swap trick

I have SMB, Tennis and Family BASIC but I never dared to try this trick. If there's a chance I'll fry something I rather not do it. Plus there's a hack somewhere that allows you to choose any one of the 255 "levels" to start at.

Author:  Myask [ Thu Jan 19, 2017 7:33 am ]
Post subject:  Re: Famicom Super Mario Bros / Tennis cart swap trick

Or use game genie codes to uncap the level select.

Author:  zeroone [ Thu Jan 19, 2017 8:06 am ]
Post subject:  Re: Famicom Super Mario Bros / Tennis cart swap trick

Pokun wrote:
I have SMB, Tennis and Family BASIC but I never dared to try this trick. If there's a chance I'll fry something I rather not do it. Plus there's a hack somewhere that allows you to choose any one of the 255 "levels" to start at.


We can safely mess around in emulation.

Since this trick requires you to reset Tennis and SMB, it is surprising that it works at all. Why didn't they program it to fully clear out memory on reset? Were they saving precious NROM bytes? SMB needs to remember the last world number to provide the continue option, but that value did not necessarily need to survive a reset.

While I have an emulator rigged up to do this, are there any other experiments I should try?

Author:  Myask [ Thu Jan 19, 2017 9:04 am ]
Post subject:  Re: Famicom Super Mario Bros / Tennis cart swap trick

The reason they don't is posted earlier in the topic…
Grapeshot wrote:
The other important aspect of this trick is that Super Mario Bros only clears RAM on startup when any of the bytes used to store the score is greater than 10 or the value of the last byte of RAM is anything other thn $A5. Tennis, being another early Nintendo game, uses the same place to store the high score and the same signature byte, so the RAM is not cleared. The same trick might work with some of the other Nintendo black box games as well depending on how much code was reused.

Reset, then, doesn't clear high-score tables.

Author:  zeroone [ Thu Jan 19, 2017 9:12 am ]
Post subject:  Re: Famicom Super Mario Bros / Tennis cart swap trick

Myask wrote:
The reason they don't is posted earlier in the topic…


Ah. Thanks.

It sounds like this trick is quite limited then. I was hoping to use Famicom BASIC like a game genie. That doesn't sound like it's going to happen.

Author:  Pokun [ Thu Jan 19, 2017 5:13 pm ]
Post subject:  Re: Famicom Super Mario Bros / Tennis cart swap trick

Family BASIC is fun for other things though.

It could work with other games that have reset-persistent data if you figure out how it detects a reset to avoid clearing RAM. Funny we just discussed clearing RAM in another thread.

zeroone wrote:
Pokun wrote:
I have SMB, Tennis and Family BASIC but I never dared to try this trick. If there's a chance I'll fry something I rather not do it. Plus there's a hack somewhere that allows you to choose any one of the 255 "levels" to start at.


We can safely mess around in emulation.

Always wanted to try this on real hardware though. But nope, not worth the risk.

Author:  rainwarrior [ Thu Jan 19, 2017 9:32 pm ]
Post subject:  Re: Famicom Super Mario Bros / Tennis cart swap trick

I think it's relatively safe (though I'm no doctor). I've hotswapped cartridges hundreds of times, haven't broken any yet.

Author:  zeroone [ Fri Jan 20, 2017 7:28 am ]
Post subject:  Re: Famicom Super Mario Bros / Tennis cart swap trick

rainwarrior wrote:
I think it's relatively safe (though I'm no doctor). I've hotswapped cartridges hundreds of times, haven't broken any yet.


Any suggestions for experiments then?

Author:  rainwarrior [ Fri Jan 20, 2017 12:53 pm ]
Post subject:  Re: Famicom Super Mario Bros / Tennis cart swap trick

zeroone wrote:
Any suggestions for experiments then?

I do it to run tests on various mappers, mostly it's been to do with famicom expansion tests.

I don't really have any suggestions, unless there's something you want to know about the hardware inside a cartridge you have. (Easier and maybe safer than socketing ROMs etc.)

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