Forums

I just dumped the bios of my old SMS PAL machine.. Now im trying to figure out how it checks if a cart is inserted or not.
Im trying to modify it so it will start the Alex Kid something game thats normally run when no cart in
inserted. Anyone have any ide how/here it checks?

Just running the BIOS in Meka or BrSMS give me garbage.

/HeroZero

Quote

> I just dumped the bios of my old SMS PAL machine.. Now im trying to figure out how it checks if a cart is inserted or not.
> Im trying to modify it so it will start the Alex Kid something game thats normally run when no cart in
> inserted. Anyone have any ide how/here it checks?

> Just running the BIOS in Meka or BrSMS give me garbage.

Are you certain you h ave a valid dump?
Post it somewhere we can take a look at it (or mail it to me) and we'll see if we can figure anything out from it.

Quote

> I just dumped the bios of my old SMS PAL machine.. Now im trying to figure out how it checks if a cart is inserted or not.
> Im trying to modify it so it will start the Alex Kid something game thats normally run when no cart in
> inserted. Anyone have any ide how/here it checks?

The SMS machines that have Alex Kidd available when no cart
is inserted don't have a BIOS. Are you saying you have
an original SMS unit that has the BIOS messages / snail game
*and* an Alex Kidd game too? To my knowledge, only the later
SMS 2 models had a built-in game.

As for the BIOS, I've always had this theory that there's
some value in C000h that indicates if a game is a cartridge
or card game. In the startup code of many games, the value
from C000h will be stored in port 3Eh, then read back and
stored again. But like I said, that's just an idea.

The Genesis docs do mention that C000h indicates the
'start up slot', which I think is a pretty clear reference
to card versus cartridge games being used. (and therefore
if a game is inserted at all, which may be how the BIOS knows
when to display an error message).

My Homepage

Quote

> As for the BIOS, I've always had this theory that there's
> some value in C000h that indicates if a game is a cartridge
> or card game. In the startup code of many games, the value
> from C000h will be stored in port 3Eh, then read back and
> stored again. But like I said, that's just an idea.
> The Genesis docs do mention that C000h indicates the
> 'start up slot', which I think is a pretty clear reference
> to card versus cartridge games being used. (and therefore
> if a game is inserted at all, which may be how the BIOS knows
> when to display an error message).

In short, the BIOS try to write different values to 3Eh and read at C000h for "an answer". When it got it it jump back to 0000h, else it continues until the last value with lead to an error or a no cartridge or a default game screen.
Which reminds me I still haven't released that damned BIOS. Everybody mailbomb me as a reminder!
I'm wondering if HeroZero has the same BIOS version. Philip Smith also dumped two other BIOS (SMS1 1988 and one from SMS2) but they are likely unperfect dumps.

Quote

> The SMS machines that have Alex Kidd available when no cart
> is inserted don't have a BIOS. Are you saying you have
> an original SMS unit that has the BIOS messages / snail game
> *and* an Alex Kidd game too? To my knowledge, only the later
> SMS 2 models had a built-in game.

im pretty sure that all sms2's have a built in game, either being alexkidd, or later ones with sonic(?)

theres 2 steps to the sms2 start up - they show a sega logo independant of the game, and then actualy start the game (internal or external). also you can get a 'software error' message in the case of a cart not inserterted correctly (only happened to me a couple of times over the years, unlike a nes that needs cart contacts to be blowen on every single time), so i guess the logo procedure handles that as well.

i am also convinced that their is two varaints of the alexkidd sms2 (i havent seen a sonic sms2, but i do remember seeing the boxes in stores just before they vanished for ever) with slightly different sega logos. the common black sms2 has an ugly logo, where as the uncommon greyer system (game gear grey you could say)which i used to own had a nicer one (at least im sure it did)

or i could be talking out of my ass telling you things you already know ;)

Author	Message
HeroZero Guest	SMS Bios Posted: Mon May 15, 2000 9:25 pm
HeroZero Guest	I just dumped the bios of my old SMS PAL machine.. Now im trying to figure out how it checks if a cart is inserted or not. Im trying to modify it so it will start the Alex Kid something game thats normally run when no cart in inserted. Anyone have any ide how/here it checks? Just running the BIOS in Meka or BrSMS give me garbage. /HeroZero

Heliophobe Site Admin Joined: 25 Oct 1999 Posts: 2029 Location: Monterey, California	Posted: Mon May 15, 2000 9:50 pm
	Quote > I just dumped the bios of my old SMS PAL machine.. Now im trying to figure out how it checks if a cart is inserted or not. > Im trying to modify it so it will start the Alex Kid something game thats normally run when no cart in > inserted. Anyone have any ide how/here it checks? > Just running the BIOS in Meka or BrSMS give me garbage. Are you certain you h ave a valid dump? Post it somewhere we can take a look at it (or mail it to me) and we'll see if we can figure anything out from it.

Charles MacDonald Joined: 28 Sep 1999 Posts: 1197	Posted: Mon May 15, 2000 11:00 pm
Charles MacDonald Joined: 28 Sep 1999 Posts: 1197	Quote > I just dumped the bios of my old SMS PAL machine.. Now im trying to figure out how it checks if a cart is inserted or not. > Im trying to modify it so it will start the Alex Kid something game thats normally run when no cart in > inserted. Anyone have any ide how/here it checks? The SMS machines that have Alex Kidd available when no cart is inserted don't have a BIOS. Are you saying you have an original SMS unit that has the BIOS messages / snail game and an Alex Kidd game too? To my knowledge, only the later SMS 2 models had a built-in game. As for the BIOS, I've always had this theory that there's some value in C000h that indicates if a game is a cartridge or card game. In the startup code of many games, the value from C000h will be stored in port 3Eh, then read back and stored again. But like I said, that's just an idea. The Genesis docs do mention that C000h indicates the 'start up slot', which I think is a pretty clear reference to card versus cartridge games being used. (and therefore if a game is inserted at all, which may be how the BIOS knows when to display an error message). My Homepage

Zoop Joined: 24 Jun 1999 Posts: 1732 Location: Paris, France	Posted: Tue May 16, 2000 5:23 am
	Quote > As for the BIOS, I've always had this theory that there's > some value in C000h that indicates if a game is a cartridge > or card game. In the startup code of many games, the value > from C000h will be stored in port 3Eh, then read back and > stored again. But like I said, that's just an idea. > The Genesis docs do mention that C000h indicates the > 'start up slot', which I think is a pretty clear reference > to card versus cartridge games being used. (and therefore > if a game is inserted at all, which may be how the BIOS knows > when to display an error message). In short, the BIOS try to write different values to 3Eh and read at C000h for "an answer". When it got it it jump back to 0000h, else it continues until the last value with lead to an error or a no cartridge or a default game screen. Which reminds me I still haven't released that damned BIOS. Everybody mailbomb me as a reminder! I'm wondering if HeroZero has the same BIOS version. Philip Smith also dumped two other BIOS (SMS1 1988 and one from SMS2) but they are likely unperfect dumps.

Limbs a Flyin' Guest	Posted: Wed May 17, 2000 4:19 pm
Limbs a Flyin' Guest	Quote > The SMS machines that have Alex Kidd available when no cart > is inserted don't have a BIOS. Are you saying you have > an original SMS unit that has the BIOS messages / snail game > and an Alex Kidd game too? To my knowledge, only the later > SMS 2 models had a built-in game. im pretty sure that all sms2's have a built in game, either being alexkidd, or later ones with sonic(?) theres 2 steps to the sms2 start up - they show a sega logo independant of the game, and then actualy start the game (internal or external). also you can get a 'software error' message in the case of a cart not inserterted correctly (only happened to me a couple of times over the years, unlike a nes that needs cart contacts to be blowen on every single time), so i guess the logo procedure handles that as well. i am also convinced that their is two varaints of the alexkidd sms2 (i havent seen a sonic sms2, but i do remember seeing the boxes in stores just before they vanished for ever) with slightly different sega logos. the common black sms2 has an ugly logo, where as the uncommon greyer system (game gear grey you could say)which i used to own had a nicer one (at least im sure it did) or i could be talking out of my ass telling you things you already know ;)

Forums

View topic - SMS Bios