On the cheats menu, enter the following codes:

Invincibility - SQUARE, SQUARE, X, TRIANGLE, X, CIRCLE, X, CIRCLE
Unlimited ammo - X, TRIANGLE, TRIANGLE, TRIANGLE, X, CIRCLE, X, SQUARE
All future weapons - X, X, X, TRIANGLE, CIRCLE, CIRCLE, SQUARE, X
All past weapons - CIRCLE, CIRCLE, TRIANGLE, SQUARE, X, TRIANGLE, TRIANGLE, SQUARE
Quadrupled damage - TRIANGLE, TRIANGLE, TRIANGLE, TRIANGLE, SQUARE, X, CIRCLE, SQUARE
Automatically complete missions - SQUARE, SQUARE, TRIANGLE, CIRCLE, CIRCLE, X, SQUARE, TRIANGLE
Fight TX Endoskeleton in every battle - TRIANGLE, SQUARE, TRIANGLE, X, TRIANGLE, TRIANGLE, TRIANGLE, TRIANGLE
50% more health in combat with TX - TRIANGLE, TRIANGLE, SQUARE, X, CIRCLE, TRIANGLE, SQUARE, CIRCLE
50% more health for TX in combat - SQUARE, TRIANGLE, SQUARE, TRIANGLE, CIRCLE, X, CIRCLE, X