All weapon upgrades:
     Pause  the  game by pressing START, then hold L and press Up, Up,
Down, Down, Left, Right, Left, Right, X, O.

Activate Invincible mode:
     Pause  the  game by pressing START, then hold L and press Up, Up,
Down, Down, Left, Left, , Right, Square, Triangle.
     When  you  exit  the  start menu, "Can't touch this" message will
appear to confirm correct code entry.

Infinite ammo:
     Pause the game by pressing START, then hold L and press Triangle,
Triangle, X, X, Square, O, Square, O, Right, Down.

Restore ammo:
     Pause the game by pressing START, then hold L and press Triangle,
Triangle, X, X, Square, O, Square, O, Down, Right.