Cheat : 

Pause the game by changing mode to pause and pressing fire, " PAUSED " will be displayed, 
Now keep pressing Joypad 2 Button 1, a sound should play and it will now show " CHEATING SWINE " 
the game is still paused, press Joypad 2 Button 1 again to unpause.

Now when you press Joypad 2 Button 1 it will display all the codes that you can use. 