MsK`
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Hi !

I started digging into the project of doing a gameboy game, up to shipping it. But I don't want to start without knowing if I can build cartridges. My first project is thus to build a sort of MBC chip, which doesn't need to be compatible with the nintendo ones so I already started thinking that it would be nice to have it also do multiplications since the GB CPU doesn't do it.

Then this morning I remembered about that AUDIO-IN pin in the cartridge pinout and thank "wow, maybe I could output a triangle wave in there ! I could have sounds as good as on NES.".
After some research I got here and found this thread : http://chipmusic.org/forums/topic/7071/ … d-channel/
I unfortunately can't bump it since I just signed up (it's wayyyy older than 3 months)

Nice idea to even put an FM synthesis chip ! But did anybody succeeded in using that pin in the end ?

BTW, I don't know anything -yet- about chip design, vhdl, fpga, cplds and all that stuff. I'm going to have to learn all that ! Any help is appreciated smile

herr_prof
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nanoloop 1.5 uses it:
http://nanoloop.com/gameboy/nanoloop15.pdf

MsK`
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Oh nice, thanks for pointing me to the manual. I'm going to send a mail to nanoloop's maker to see if I can get some more info. Thanks smile

MsK`
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I found in nintendo's official manual this : "The VIN terminal can be used normally only in CGB. (Since the signal from the VIN terminal is too low to be used, the VIN terminal cannot be used in DMG.)"
Can anybody confirm ?

kitsch
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it can be used fine on/with a DMG

you need to search "pandocs gameboy", everything you'd need to access/use VIN will be in there. 

kk_gb_8m cartridge uses this pin, as well as another cart i've not announced yet.  its very doable.

MsK`
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Ah cool ! Another cart using it smile

There is still good stuff to get from nintendo's doc, well if they are true, but it makes sense. They mention that the total output should not exceed 3V and that the 4 built in channels already output up to 0.75V (4 x 0.75V = 3V). So software should prevent that and max output to 0.6V for the built-in channels so that the VIN can output up to 0.6V and total stays less than 3V (5 x 0.6V = 3V). So I guess that software using VIN should not put an audio volume higher than 12.8 on each channel, which would mean 0xC or 0xD.

Last edited by MsK` (Aug 29, 2014 12:13 pm)