This is a (currently mostly unannotated) disassembly of the firmware of the Yamaha TX81Z synthesizer.

I believe I've identified and separated most of the code and data blocks.

The files are designed to be assembled using the A09 assembler maintained by Hermann Sieb.

The firmware is split into two halves, both of which are mapped from $8000 - $ffff in the memory space, with the bank selected via GPIO pin P63.

Generating a new firmware image requires that the two resulting 32kB binaries be concatenated and burned to a single 27C512 (64kB) EPROM.