At the title screen, press Start. When you see the words, Game Start and Config Mode, press Up, Down, Left, Right
At the main screen, press Up, Down, Left, Right, Right, Up
With the stage select code, press A + B + C to see the game's hex code on the screen.
At the title screen menu press left, right, A+B+C and you will hear a sound effect, then press B,A,C,A, left, left, right, left - now you will be invincible!