changing SMS builtin game

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Does anyone know if its possible to swap the sega master system bios with
that of a game cart. How could I change the built in game to whatever I
like.

 

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I didn't know the SMS had a built in game! What is it?

 

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"The Space Boss" <drsmith666@aol.com> wrote in message
news:1111367480.274886.6870@z14g2000cwz.googlegroups.com...
> I didn't know the SMS had a built in game! What is it?
>


[1] I'VE HEARD ABOUT A BUILT-IN, HIDDEN GAME? WHAT GIVES?

The original model of the SMS has a built in, code accessible maze game;
your goal is to guide a small snail through a series of different levels.
Not much play value, but it's a nice extra to have.

If you own an original model SMS without a built in game...
Turn on your SMS and wait for the instruction screen to appear. With
controller 1, press up and hold buttons 1 and 2.

If you own an original model SMS with a built in game...
First, hold down the sequence given above. While holding, turn the machine
on and wait.

The SMS II (and possibly late released versions of the SMS I with 2
games built-in) do not have the snail maze game. from:
http/www.classicgaming.com/museum/faqs/smsfaq.shtml

 

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>Does anyone know if its possible to swap the sega master system bios with
>that of a game cart. How could I change the built in game to whatever I
>like.

I don't really know much about the SMS internals, but this is almost
certainly impossible. To put it simply, for the above to work, the boot
rom and the snail game rom would, at the very least, have to be seperate
chips. This is highly unlikely. They probably had an extra 100 bytes on
the boot ROM and just slipped the game in there for fun/testing.
Perhaps if you had an extremly in depth understanding of the SMS boot rom
you could burn a new (larger) EPROM that included the boot ROM at all the
right addresses and a jump to your new game... but, even that is likely to
be impossible.
I understand there are some SMSs that included different, full-fledged
builtin games, such as Sonic the Hedgehog. These systems are at least
marginally more likely to have a seperate game ROM you could switch out.
I still wouldn't bet on it though.
--
Jim Leek
jrleek@soda.berkeley.edu