Hold Down/Left + I + II and press Run. Alternatively, hold
Down + Select before the stage text appears. Release the buttons
when your ship stops flashing to be invincible while your
weapons are at level one.
Press Select at the title screen to enter the options menu.
Highlight the "Exit" option, then press Down, II,
II, Left, I, Right, Select. A sound and red background letters
will confirm correct code entry.