Old game machine shows Doom, but new plug-in does the work

Jason Kopp made Doom appear on a Vectrex, a 1982 game machine with its own small screen. All the work is done by a new plug-in he built, the Ultimate Vectrex Multicart 2. The old machine acts only as a screen for the sharp lines. Sound comes from a separate earphone plug on the new part, not the old machine.