Zylogic's USB Solution describes how to implement a full-speed USB device application using the Future Technology Devices Intl. (FDTI) 1.x USB Controller, FT8U245AM. A full reference design contains low-level software drivers and schematic diagrams.

Application Notes:
AN19: An ZE5 Full-Speed USB Reference Design Using the FTDI FT8U245AM USB 1.x Controller (453K)

Reference Designs:
RFD-03: ZE5+USB (.zip, 2.3MB)