The XSPICE option allows you to add event-driven simulation capabilities to NGSPICE. NGSPICE now is the main software program that performs mathematical simulation of a circuit specified by you, the user. It takes input in the form of commands and circuit descriptions and produces output data (e.g. voltages, currents, digital states, and waveforms) that describe the circuit’s behavior.

Plain NGSPICE is designed for analog simulation and is based exclusively on matrix solution techniques. The XSPICE option adds even-driven simulation capabilities. Thus, designs that contain significant portions of digital circuitry can be efficiently simulated together with analog components. NGSPICE with XSPICE option also includes a `User-Defined Node' capability that allows event-driven simulations to be carried out with any type of data.

The XSPICE option has been developed by the Computer Science and Information Technology Laboratory at Georgia Tech Research Institute of the Georgia Institute of Technology, Atlanta, Georgia 30332 at around 1990 and enhanced by the NGSPICE team. The manual is based on the original XSPICE user's manual, no longer available from Georgia Tech, but from the ngspice web site.

In the following, the term `XSPICE' may be read as `NGSPICE with XSPICE code model subsystem enabled'. You may enable the option by adding --enable-xspice to the ./configure command. The MS Windows distribution already contains the XSPICE option.