see https://www.pedelecforum.de/forum/index.php?threads/yamaha-reverse-engineering.39480/page-12 version 4 of my dongle, suited for smt assembly service.

to program it get a arduino uno and flash it wit arduinoISP, then look up how to connect a attiny13 to arduinoisp (i use a eeprom clamp and jumper wires for this) install MicroCore for arduino ide, in arduino ide, select attiny13 and external 8mhz clock burn bootloader otherwise the ext. clock wont be used.

select programmer: arduino as isp, paste code from here : https://pastebin.com/0YXUpnaG and hit upload, if its all connected correctly it should work (writing, validating, finished) its a good idea to check with a logic analyzer if the timings are correct. adjust the #defines in the top of the code accordingly. if its totally off, you might run on internal clock, do the burn bootloader step again after selecting ext. 8mhz.