GBC over/underclocking

[Burbruee]

Hello,

I'm thinking about modding my GBC and replacing the crystal.
I was looking at this guide right here

Well, I want to do things a bit different. I want to both over AND underclock my gameboy.

So, if the original GBC uses a ~8 MHz crystal, then a 4 MHz crystal should do ok for making things run slower, and I was thinking of a 20 MHz crystal for turbo.
Ok, the guide says don't go above ~16 MHz, but I saw this video (though using a Sparta3-board) and 20 MHz looks safe.

I was wondering, can I keep the original crystal and put in TWO other crystals? What type of switch/es would I use, and how would I wire it? So I can switch between slow, normal and fast speed.

Thanks.

[themadhacker]

yeah, you can put in two other crystals.

The only reason I didn't really recommend going over 16 was because doing so would make the games so fast that they would be unplayable.

[Burbruee]

Yeah, I figured. I remember playing Pokemon Stadium with the Dodrio gameboy on the Nintendo 64 which I think is 3x speed and it is pretty fast and sometimes hard to go in a specific spot but I got kind of used to it (to the point where 2x started to feel too slow)

So I'll probably go with 20.

[Master Kirby]

Hello,
I was wondering, can I keep the original crystal and put in TWO other crystals? What type of switch/es would I use, and how would I wire it? So I can switch between slow, normal and fast speed.

Thanks.

If you want to underclock the GBC, you will need to remove the original crystal since the GBA will run at the speed of the fasted crystal that is attached. If you can remove it without causing damage, you could reuse it, otherwise you will need to use a different crystal for ~8 MHZ if you break the original.

You will need to use a three-way switch to change between the three speeds.
_ Connect one contact from each of the three crystals to one contact where the original crystal connected to the GBC.
_ Connect the three positions of the switch to the other contacts of the three crystals so it can change continuity among the 3 crystals, to a single contact of the switch.
_ Connect the single contact of the switch to the other contact where the original crystal connected to the GBC's board.
_You're done.