DR. SPICE includes the XSPICE code model technology which was developed at the Georgia Institute of Technology. This simulation and modeling technology extends the ability of DR. SPICE to model a circuit’s functionality at a high level of abstraction. There are 3 categories of code models: analog, digital and mixed analog/digital. The XSPICE technology includes a 12 state digital simulator embedded within DR. SPICE. Another feature of the XSPICE technology allows the user to develop models in the “C” programming language. These user-developed models are dynamically linked into DR. SPICE during a simulation.
By using a code model in your design, the user is gaining a potentially large (1000X) increase in simulation speed. The draw-back is that simulation accuracy is reduced. By having a well thought out Simulation methodology, the reduction in simulation accuracy can be negligible.