Thanks to Sean Riddle (https://seanriddle.com), the source code attached to the original Furby patent is now public!
See: https://archive.org/details/furby-source.
The 1998 Furby is based on a SPC81A (a microcontroller based on 6502) and TI50C04, the sound chip from Texas Instruments which is used as the I/O co-processor beside its main purpose of producing sound.
The source code only deals with the main CPU (however, the co-processor's communication protocol is also described there).
It's a bit inconsistent, with references to some labels that aren't declared anywhere, but the code is well-commented and the comments explain the design well.
And no, I haven't been able to find any easter eggs that weren't known before.
See: https://archive.org/details/furby-source.
The 1998 Furby is based on a SPC81A (a microcontroller based on 6502) and TI50C04, the sound chip from Texas Instruments which is used as the I/O co-processor beside its main purpose of producing sound.
The source code only deals with the main CPU (however, the co-processor's communication protocol is also described there).
It's a bit inconsistent, with references to some labels that aren't declared anywhere, but the code is well-commented and the comments explain the design well.
And no, I haven't been able to find any easter eggs that weren't known before.