There was a TON of discussion about this before. Apparently there's also a SEGA chip on there which seems to be the problem with making your own. I'll see if I can dig those posts up.
http://www.dcemulation.com/phpBB/vie...&highlight=bba
http://www.dcemulation.com/phpBB/vie...t=bba&start=20
I'm sure there's more, but that should answer most of your questions.
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