What is the difference between hammurabi's code and the twelve tablets?

Well, firstly, they're completely different law sets that were written hundreds of years apart.

The Twelve Tables were Rome's Constitution-like law codes. They were written and amended by many people and government terms/years. It is closer to modern law when considering the fact that it actually recognizes trial.

Hammurabi's Code is a Babylonian law code collected in a timely manner by one person: Hammurabi. Despite the fact that it's older than the Twelve Tables, the Code of Hammurabi is much more specific and recognizes people's rights (aside from trial) much better.