A circuit block that appears more than once in the overall circuit and consists of SPICE elements can be defined as a subcircuit. The block can be then referenced as a single component or as a subcircuit instance, and connected throughout the circuit.

Users who have already used SPICE may have a number of netlist files containing subcircuits. These subcircuits can also be used in EDSpice Simulator. In order to use this netlist files with EDSpice we have to extract subcircuits from netlist files and append them to the subcircuit library.

The Subcircuit Adapter converts the existing SPICE subcircuits to EDSpice format. A header is added to the subcircuit as SPICE comment lines. This allows a subcircuit to be assigned to a symbol in the Interactive Module, while maintaining compatibility with any other version of SPICE. The adaptation procedure is necessary as it ensures that each subcircuit stored in the subcircuit library has a proper header, without this header, the link from a subcircuit to its symbol would be impossible. Headers are used internally by EDSpice to aid the user in linking subcircuits to circuit elements.

Files in the subcircuit library are stored as plain ASCII text files and as such may be appended manually (if required) to any SPICE netlist file for input to other SPICE simulators.