This is the schematic for the V2's controller, you can click on the image for the full size version.

There are 28 keys on the V2's controller, most of these are wired in to a 4x7 matrix arrangement. The lines can be accessed from the underside of the circuit board.

Controller Key Matrix
Address Line
Key Line
Name
 Function
Addres Line
Key Line
Name
 Function
A0
B0
SW1
 Right Stick Up
A2
B0
SW15
 Right Stick Down
A0
B1
SW2
 Right Stick Up/Right
A2
B1
SW16
 "D"
A0
B2
SW3
 Right Stick Up/Left
A2
B2
SW17
 "Z"
A0
B3
SW4
 Right Stick Right
A2
B3
SW18
 "X"
A0
B4
SW5
 Right Stick Left
A2
B4
SW19
 "Y"
A0
B5
SW6
 Right Stick Down/Right
A2
B5
SW20
 Left Stick Down
A0
B6
SW7
 Right Stick Down/Legt
A2
B6
Shift 4
 Laser
A1
B0
SW8
 Left Stick Up
A3
B0
SW24
 Stop
A1
B1
SW9
 Left Stick Up/Right
A3
B1
SW25
 "C"
A1
B2
SW10
 Left Stick Up/Left
A3
B2
SW26
 "A"
A1
B3
SW11
 Left Stick Right
A3
B3
SW27
 "B"
A1
B4
SW12
 Left Stick Left
A3
B4
N/A
 N/A
A1
B5
SW13
 Left Stick Down/Right
A3
B5
N/A
 N/A
A1
B6
SW14
 Left Stick Down/Left
A3
B6
N/A
 N/A