Enter the folloing codes at the 'Options' screen to enable the corresponding effect.
Press and hold R1, and press Up, Right, Down, Left, Up, Right, Down, Left and Up.
Auto Rapid Fire Mode:
Press and hold L1, and press Triangle, O, X, Square, Triangle, O, X, Square and Triangle.
More Credits (9):
Press and hold L1+R1 and press Triangle, Square, X, O, Triangle, Up, Left, Down, Right and Up.