The original patent for the 1998 Furbys had an appendix containing the incomplete source code of the firmware for the main processor, the 6502-derived Sunplus SPC81A.
However, it wasn't available on any online resources, even those of the USPTO itself.
Around August 2018, it became known that Sean Riddle, a member of a MAME developers' forum, had contacted the US patent office and obtained a copy of the patent wrapper which indeed contained the source code appendix.
Sean was eventually asked to publish it online and the 300-page document can now be found on archive.org: https://archive.org/details/furby-source.
Observations[]
- There's quite a lot of humorous comments in the code, like:
On power up or reset, Furby must go select a new name ,,, ahw how cute.
- The code also shows that there originally were only 15 Furby names, with 9 newer ones (such as Toh-Loo-Kah) added later.