Here's what I've gathered, it's built on other people's work. I'd put it on the Wiki but it seems they aren't accepting new users.
Name Binary Hex
L 1111110111111111 FDFF
R 1111111011111111 FEFF
Down 1111111101111111 FF7F
Up 1111111110111111 FFBF
Right? 1111111111011111 FFDF
Left? 1111111111101111 FFEF
Start 1111111111110111 FFF7
Select 1111111111111011 FFFB
B 1111111111111101 FFFD
A? 1111111111111110 FFFE
? means I'm not sure and just guessing
And for multiple button press
B > A
A & B = Button
B - (A - B) = C