does using a cheat code negate getting a trophy?

[thetonestarr]

It depends on the cheat and the achievement/trophy. For instance, GTAIV's bridge achievement isn't negated if you use the cheat to get the helicopter, instead of getting it legitimately. And again, in GTAIV, if you use the cheat for full ammo, it won't stop you from completing [most] achievements. Don't use the cheat for full ammo + full health, though - that one DOES affect most achievements.

It basically depends on if the cheat directly affects you getting the achievement/trophy or not.