Transfer PAK

References:

The Best Documentation I've found on the Transfer PAK

https://github.com/joeldipops/TransferBoy/blob/master/docs/TransferPakReference.md

A few more tidbits, but very incomplete compared to the above.

https://sourceforge.net/p/nragev20/code/HEAD/tree/docs/Transfer%20Pak%20Stuff/

Everdrive 5v to 3v3 modification.

http://krikzz.com/forum/index.php?topic=1780.75

https://www.dropbox.com/s/hei9yi4618manin/E64TPMOD.pdf switch modification.

https://imgur.com/6ske7Mb Soldered modification.