Pocket Heaven

CKY-2K · Posted: Fri Dec 14, 2007 9:23 pm Post subject: GB Micro does have GBC support?

Weeks ago, when I played with the Goomba Emulator, it crashed and showed the GBC bios boot up, but the screen was at the topleft of the display, but you could still stretch out the screen with shoulder buttons.

Weird huh?
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Hypershell · Member Joined: 09 Dec 2005 Posts: 166

I've heard of crashing the Micro into GBC mode before. Not entirely sure what the deal with that is, though. I can't imagine why the GBC logo would be in the Micro.
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dantheman · Posted: Sat Dec 15, 2007 4:42 pm Post subject:

The GBM contains at the very least the GBC sound engine, as several GBA games make use of it, but as the main z80 processor is absent I doubt you'll be able to get much farther than crashing it to show the GBC BIOS.

Dwedit · Posted: Sat Dec 15, 2007 7:22 pm Post subject:

Fact:
If it's showing the GBC bios, then there is a GBZ80 in there.

Speculation:
Nintendo didn't bother changing the GBA chips at all, and left everything alone. It would probably cost more to change stuff than to make special reduced-functionality versions.
I haven't looked at a GB Micro circuit board but I suspect that Nintendo just removed all the GBC traces on the PCB, and related components, leaving the GBC mode still intact in the main GBA processor.
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Bibin · Member Joined: 18 Sep 2005 Posts: 456

They probably just removed that switch in the cartslot that puts it to GBC mode. Perhaps I can open my regular GBA and find out what that leads to, and manually enable it on my micro.

...If my micro came with a charger, this would all be easier. It's difficult to play a GB micro when it doesn't last for more than 8 seconds.

I can't get my gameboy micro to open with my triwing screwdriver; the screws are too tiny, so I give you a google images [s]rip[/s] borrow.

More pics:

http://pc.watch.impress.co.jp/docs/2005/0913/gameboy.htm

Chishm · Posted: Sun Dec 16, 2007 6:27 am Post subject:

It's interesting that the CPU is marked AGB and not OXY, suggesting that they did indeed keep the same chip. Nintendo probably just didn't include the components required for GB(C) game pak operation, such as the 5V voltage converters.
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Bibin · Member Joined: 18 Sep 2005 Posts: 456

Could this be circumvented with a bit of knowledge, soldering, and parts? Also, this could also apply to the DS.

Chishm · Posted: Mon Dec 17, 2007 8:31 am Post subject:

Hypershell · Member Joined: 09 Dec 2005 Posts: 166

So, voltage converter and a few traces were all that was removed? Man, that blows. GBC compatibility was literally the deciding factor for me between the Micro and a backlit SP. I did like the Micro's look and faceplates, not to mention I wouldn't have had to keep a headphone adapter in my pockets.
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Gunnex · Posted: Tue Jan 08, 2008 1:18 am Post subject:

The other thing is the fact that the Micro is tiny. I have so many pockets that my SP, DS, or PSP won't fit into, but the Micro does. I also was able to use an old cell phone case on it, which would be great for music playback (if I had an M3 instead of a GBAMP >_<)

But the SP does GCN > GBA with no problem. As for GBM, you have to make a cable yourself.
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CKY-2K · Posted: Wed Jan 16, 2008 10:25 am Post subject:

Bibin · Member Joined: 18 Sep 2005 Posts: 456

Me three. Would it not be possible to restore some basic traces? Voltage conversion should not be too hard to do, just a little hard to fit it all in the case.

Hypershell · Member Joined: 09 Dec 2005 Posts: 166

The cramped housing alone is probably reason enough to thwart such efforts. Besides the fact that while soldering on such a cramped board it would be extremely easy to fark something up, I sincerely doubt that the number of parts and wires you'd need would fit within the GBM housing.

To add to that, I don't think accommodating the voltage change would be at all simple, either. It's not just the switch, if I understand this right (someone correct me if I don't), the bit in a GBA/SP/Player is not a converter but rather a switch to a different electrical circuit within the system. You would essentially have to install the entire 5V circuit. Can't mix with GBM connections since that would fry them.

I wonder, though, could one try modding a flash card rather than the system? Suppose some homebrew coder could figure out how to intentionally kick the GBM into GBC mode (which I'd imagine would be the hard part). Would it be possible to flash a GBA card with a GBC menu, thus bypassing the voltage issue? You could boot a program to make the switch on the GBM either with an unmodded card or through a link cable program (I don't know how well the GBA tolerates switching cartridges), insert the modded flash card, and then switch modes. Could that work?
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Dwedit · Posted: Mon Jan 21, 2008 4:17 am Post subject:

As far as I know, the GBC and GBA use a different protocol on the cartridge bus. You'd need a card which would perform the reads and writes the same way as a GBC cartridge.
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tepples · Posted: Mon Jan 21, 2008 3:01 pm Post subject:

True, but the GBC protocol is similar to the GBA SRAM protocol, with about three or four enable lines switched around. I'd bet that's how the Flash2Advance GB Bridge got away with it. If someone's serious about this, I'd recommend taking a logic analyzer, logging the startup sequence of a GBC, and logging the same parts of the startup sequence of a micro that has crashed into GBC mode.
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