Two continues:
Hold I and press II at the title screen. You will hear a sound if you have entered the code correctly.

One hundred continues:
Press Down, Right, Select, Down, II, Down, I, Left, Select, Up, I, II, I at the title screen. Press Run to begin game play.

Arcade mode screen:
Hold Select and press Run 57 times to reset the game for a narrow screen.

Sound test:
Press Left, Right, Down, Up, Select, Left at the title screen.